binutils-gdb/gdb/infcall.h

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2003-04-21 18:48:41 +02:00
/* Perform an inferior function call, for GDB, the GNU debugger.
Copyright (C) 2003-2018 Free Software Foundation, Inc.
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This file is part of GDB.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>. */
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#ifndef INFCALL_H
#define INFCALL_H
#include "dummy-frame.h"
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struct value;
struct type;
Calling ifunc functions when target has no debug info but resolver has After the previous patch, on Fedora 27 (glibc 2.26), if you try calling strlen in the inferior, you now get: (top-gdb) p strlen ("hello") '__strlen_avx2' has unknown return type; cast the call to its declared return type This is correct, because __strlen_avx2 is written in assembly. We can improve on this though -- if the final ifunc resolved/target function has no debug info, but the ifunc _resolver_ does have debug info, we can try extracting the final function's type from the type that the resolver returns. E.g.,: typedef size_t (*strlen_t) (const char*); size_t my_strlen (const char *) { /* some implementation */ } strlen_t strlen_resolver (unsigned long hwcap) { return my_strlen; } extern size_t strlen (const char *s); __typeof (strlen) strlen __attribute__ ((ifunc ("strlen_resolver"))); In the strlen example above, the resolver returns strlen_t, which is a typedef for pointer to a function that returns size_t. "strlen_t" is the type of both the user-visible "strlen", and of the the target function that implements it. This patch teaches GDB to extract that type. This is done for actual inferior function calls (in infcall.c), and for ptype (in eval_call). By the time we get to either of these places, we've already lost the original symbol/minsym, and only have values and types to work with. Hence the changes to c-exp.y and evaluate_var_msym_value, to ensure that we propagate the ifunc minsymbol's info. The change to make ifunc symbols have no/unknown return type exposes a latent problem -- gdb.compile/compile-ifunc.exp calls a no-debug-info function, but we did not warn about it. The test is fixed by this commit too. gdb/ChangeLog: 2018-04-26 Pedro Alves <palves@redhat.com> * blockframe.c (find_gnu_ifunc_target_type): New function. (find_function_type): New. * eval.c (evaluate_var_msym_value): For GNU ifunc types, always return a value with a memory address. (eval_call): For calls to GNU ifunc functions, try to find the type of the target function from the type that the resolver returns. * gdbtypes.c (objfile_type): Don't install a return type for ifunc symbols. * infcall.c (find_function_return_type): Delete. (find_function_addr): Add 'function_type' parameter. For calls to GNU ifunc functions, try to find the type of the target function from the type that the resolver returns, and return it via FUNCTION_TYPE. (call_function_by_hand_dummy): Adjust to use the function type returned by find_function_addr. (find_function_addr): Add 'function_type' parameter and move description here. * symtab.h (find_function_type, find_gnu_ifunc_target_type): New declarations. gdb/testsuite/ChangeLog: 2018-04-26 Pedro Alves <palves@redhat.com> * gdb.compile/compile-ifunc.exp: Also expect "function has unknown return type" warnings.
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/* Determine a function's address and its return type from its value.
If the function is a GNU ifunc, then return the address of the
target function, and set *FUNCTION_TYPE to the target function's
type, and *RETVAL_TYPE to the target function's return type.
Calls error() if the function is not valid for calling. */
extern CORE_ADDR find_function_addr (struct value *function,
Calling ifunc functions when target has no debug info but resolver has After the previous patch, on Fedora 27 (glibc 2.26), if you try calling strlen in the inferior, you now get: (top-gdb) p strlen ("hello") '__strlen_avx2' has unknown return type; cast the call to its declared return type This is correct, because __strlen_avx2 is written in assembly. We can improve on this though -- if the final ifunc resolved/target function has no debug info, but the ifunc _resolver_ does have debug info, we can try extracting the final function's type from the type that the resolver returns. E.g.,: typedef size_t (*strlen_t) (const char*); size_t my_strlen (const char *) { /* some implementation */ } strlen_t strlen_resolver (unsigned long hwcap) { return my_strlen; } extern size_t strlen (const char *s); __typeof (strlen) strlen __attribute__ ((ifunc ("strlen_resolver"))); In the strlen example above, the resolver returns strlen_t, which is a typedef for pointer to a function that returns size_t. "strlen_t" is the type of both the user-visible "strlen", and of the the target function that implements it. This patch teaches GDB to extract that type. This is done for actual inferior function calls (in infcall.c), and for ptype (in eval_call). By the time we get to either of these places, we've already lost the original symbol/minsym, and only have values and types to work with. Hence the changes to c-exp.y and evaluate_var_msym_value, to ensure that we propagate the ifunc minsymbol's info. The change to make ifunc symbols have no/unknown return type exposes a latent problem -- gdb.compile/compile-ifunc.exp calls a no-debug-info function, but we did not warn about it. The test is fixed by this commit too. gdb/ChangeLog: 2018-04-26 Pedro Alves <palves@redhat.com> * blockframe.c (find_gnu_ifunc_target_type): New function. (find_function_type): New. * eval.c (evaluate_var_msym_value): For GNU ifunc types, always return a value with a memory address. (eval_call): For calls to GNU ifunc functions, try to find the type of the target function from the type that the resolver returns. * gdbtypes.c (objfile_type): Don't install a return type for ifunc symbols. * infcall.c (find_function_return_type): Delete. (find_function_addr): Add 'function_type' parameter. For calls to GNU ifunc functions, try to find the type of the target function from the type that the resolver returns, and return it via FUNCTION_TYPE. (call_function_by_hand_dummy): Adjust to use the function type returned by find_function_addr. (find_function_addr): Add 'function_type' parameter and move description here. * symtab.h (find_function_type, find_gnu_ifunc_target_type): New declarations. gdb/testsuite/ChangeLog: 2018-04-26 Pedro Alves <palves@redhat.com> * gdb.compile/compile-ifunc.exp: Also expect "function has unknown return type" warnings.
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struct type **retval_type,
struct type **function_type = NULL);
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/* Perform a function call in the inferior.
ARGS is a vector of values of arguments (NARGS of them). FUNCTION
is a value, the function to be called. Returns a value
representing what the function returned. May fail to return, if a
breakpoint or signal is hit during the execution of the function.
Stop assuming no-debug-info functions return int The fact that GDB defaults to assuming that functions return int, when it has no debug info for the function has been a recurring source of user confusion. Recently this came up on the errno pretty printer discussions. Shortly after, it came up again on IRC, with someone wondering why does getenv() in GDB return a negative int: (gdb) p getenv("PATH") $1 = -6185 This question (with s/getenv/random-other-C-runtime-function) is a FAQ on IRC. The reason for the above is: (gdb) p getenv $2 = {<text variable, no debug info>} 0x7ffff7751d80 <getenv> (gdb) ptype getenv type = int () ... which means that GDB truncated the 64-bit pointer that is actually returned from getent to 32-bit, and then sign-extended it: (gdb) p /x -6185 $6 = 0xffffe7d7 The workaround is to cast the function to the right type, like: (gdb) p ((char *(*) (const char *)) getenv) ("PATH") $3 = 0x7fffffffe7d7 "/usr/local/bin:/"... IMO, we should do better than this. I see the "assume-int" issue the same way I see printing bogus values for optimized-out variables instead of "<optimized out>" -- I'd much rather that the debugger tells me "I don't know" and tells me how to fix it than showing me bogus misleading results, making me go around tilting at windmills. If GDB prints a signed integer when you're expecting a pointer or aggregate, you at least have some sense that something is off, but consider the case of the function actually returning a 64-bit integer. For example, compile this without debug info: unsigned long long function () { return 0x7fffffffffffffff; } Currently, with pristine GDB, you get: (gdb) p function () $1 = -1 # incorrect (gdb) p /x function () $2 = 0xffffffff # incorrect maybe after spending a few hours debugging you suspect something is wrong with that -1, and do: (gdb) ptype function type = int () and maybe, just maybe, you realize that the function actually returns unsigned long long. And you try to fix it with: (gdb) p /x (unsigned long long) function () $3 = 0xffffffffffffffff # incorrect ... which still produces the wrong result, because GDB simply applied int to unsigned long long conversion. Meaning, it sign-extended the integer that it extracted from the return of the function, to 64-bits. and then maybe, after asking around on IRC, you realize you have to cast the function to a pointer of the right type, and call that. It won't be easy, but after a few missteps, you'll get to it: ..... (gdb) p /x ((unsigned long long(*) ()) function) () $666 = 0x7fffffffffffffff # finally! :-) So to improve on the user experience, this patch does the following (interrelated) things: - makes no-debug-info functions no longer default to "int" as return type. Instead, they're left with NULL/"<unknown return type>" return type. (gdb) ptype getenv type = <unknown return type> () - makes calling a function with unknown return type an error. (gdb) p getenv ("PATH") 'getenv' has unknown return type; cast the call to its declared return type - and then to make it easier to call the function, makes it possible to _only_ cast the return of the function to the right type, instead of having to cast the function to a function pointer: (gdb) p (char *) getenv ("PATH") # now Just Works $3 = 0x7fffffffe7d7 "/usr/local/bin:/"... (gdb) p ((char *(*) (const char *)) getenv) ("PATH") # continues working $4 = 0x7fffffffe7d7 "/usr/local/bin:/"... I.e., it makes GDB default the function's return type to the type of the cast, and the function's parameters to the type of the arguments passed down. After this patch, here's what you'll get for the "unsigned long long" example above: (gdb) p function () 'function' has unknown return type; cast the call to its declared return type (gdb) p /x (unsigned long long) function () $4 = 0x7fffffffffffffff # correct! Note that while with "print" GDB shows the name of the function that has the problem: (gdb) p getenv ("PATH") 'getenv' has unknown return type; cast the call to its declared return type which can by handy in more complicated expressions, "ptype" does not: (gdb) ptype getenv ("PATH") function has unknown return type; cast the call to its declared return type This will be fixed in the next patch. gdb/ChangeLog: 2017-09-04 Pedro Alves <palves@redhat.com> * ada-lang.c (ada_evaluate_subexp) <TYPE_CODE_FUNC>: Don't handle TYPE_GNU_IFUNC specially here. Throw error if return type is unknown. * ada-typeprint.c (print_func_type): Handle functions with unknown return type. * c-typeprint.c (c_type_print_base): Handle functions and methods with unknown return type. * compile/compile-c-symbols.c (convert_symbol_bmsym) <mst_text_gnu_ifunc>: Use nodebug_text_gnu_ifunc_symbol. * compile/compile-c-types.c: Include "objfiles.h". (convert_func): For functions with unknown return type, warn and default to int. * compile/compile-object-run.c (compile_object_run): Adjust call to call_function_by_hand_dummy. * elfread.c (elf_gnu_ifunc_resolve_addr): Adjust call to call_function_by_hand. * eval.c (evaluate_subexp_standard): Adjust calls to call_function_by_hand. Handle functions and methods with unknown return type. Pass expect_type to call_function_by_hand. * f-typeprint.c (f_type_print_base): Handle functions with unknown return type. * gcore.c (call_target_sbrk): Adjust call to call_function_by_hand. * gdbtypes.c (objfile_type): Leave nodebug text symbol with NULL return type instead of int. Make nodebug_text_gnu_ifunc_symbol be an integer address type instead of nodebug. * guile/scm-value.c (gdbscm_value_call): Adjust call to call_function_by_hand. * infcall.c (error_call_unknown_return_type): New function. (call_function_by_hand): New "default_return_type" parameter. Pass it down. (call_function_by_hand_dummy): New "default_return_type" parameter. Use it instead of defaulting to int. If there's no default and the return type is unknown, throw an error. If there's a default return type, and the called function has no debug info, then assume the function is prototyped. * infcall.h (call_function_by_hand, call_function_by_hand_dummy): New "default_return_type" parameter. (error_call_unknown_return_type): New declaration. * linux-fork.c (call_lseek): Cast return type of lseek. (inferior_call_waitpid, checkpoint_command): Adjust calls to call_function_by_hand. * linux-tdep.c (linux_infcall_mmap, linux_infcall_munmap): Adjust calls to call_function_by_hand. * m2-typeprint.c (m2_procedure): Handle functions with unknown return type. * objc-lang.c (lookup_objc_class, lookup_child_selector) (value_nsstring, print_object_command): Adjust calls to call_function_by_hand. * p-typeprint.c (pascal_type_print_varspec_prefix): Handle functions with unknown return type. (pascal_type_print_func_varspec_suffix): New function. (pascal_type_print_varspec_suffix) <TYPE_CODE_FUNC, TYPE_CODE_METHOD>: Use it. * python/py-value.c (valpy_call): Adjust call to call_function_by_hand. * rust-lang.c (rust_evaluate_funcall): Adjust call to call_function_by_hand. * valarith.c (value_x_binop, value_x_unop): Adjust calls to call_function_by_hand. * valops.c (value_allocate_space_in_inferior): Adjust call to call_function_by_hand. * typeprint.c (type_print_unknown_return_type): New function. * typeprint.h (type_print_unknown_return_type): New declaration. gdb/testsuite/ChangeLog: 2017-09-04 Pedro Alves <palves@redhat.com> * gdb.base/break-main-file-remove-fail.exp (test_remove_bp): Cast return type of munmap in infcall. * gdb.base/break-probes.exp: Cast return type of foo in infcall. * gdb.base/checkpoint.exp: Simplify using for loop. Cast return type of ftell in infcall. * gdb.base/dprintf-detach.exp (dprintf_detach_test): Cast return type of getpid in infcall. * gdb.base/infcall-exec.exp: Cast return type of execlp in infcall. * gdb.base/info-os.exp: Cast return type of getpid in infcall. Bail on failure to extract the pid. * gdb.base/nodebug.c: #include <stdint.h>. (multf, multf_noproto, mult, mult_noproto, add8, add8_noproto): New functions. * gdb.base/nodebug.exp (test_call_promotion): New procedure. Change expected output of print/whatis/ptype with functions with no debug info. Test all supported languages. Call test_call_promotion. * gdb.compile/compile.exp: Adjust expected output to expect warning. * gdb.threads/siginfo-threads.exp: Likewise.
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DFEAULT_RETURN_TYPE is used as function return type if the return
type is unknown. This is used when calling functions with no debug
info.
ARGS is modified to contain coerced values. */
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Stop assuming no-debug-info functions return int The fact that GDB defaults to assuming that functions return int, when it has no debug info for the function has been a recurring source of user confusion. Recently this came up on the errno pretty printer discussions. Shortly after, it came up again on IRC, with someone wondering why does getenv() in GDB return a negative int: (gdb) p getenv("PATH") $1 = -6185 This question (with s/getenv/random-other-C-runtime-function) is a FAQ on IRC. The reason for the above is: (gdb) p getenv $2 = {<text variable, no debug info>} 0x7ffff7751d80 <getenv> (gdb) ptype getenv type = int () ... which means that GDB truncated the 64-bit pointer that is actually returned from getent to 32-bit, and then sign-extended it: (gdb) p /x -6185 $6 = 0xffffe7d7 The workaround is to cast the function to the right type, like: (gdb) p ((char *(*) (const char *)) getenv) ("PATH") $3 = 0x7fffffffe7d7 "/usr/local/bin:/"... IMO, we should do better than this. I see the "assume-int" issue the same way I see printing bogus values for optimized-out variables instead of "<optimized out>" -- I'd much rather that the debugger tells me "I don't know" and tells me how to fix it than showing me bogus misleading results, making me go around tilting at windmills. If GDB prints a signed integer when you're expecting a pointer or aggregate, you at least have some sense that something is off, but consider the case of the function actually returning a 64-bit integer. For example, compile this without debug info: unsigned long long function () { return 0x7fffffffffffffff; } Currently, with pristine GDB, you get: (gdb) p function () $1 = -1 # incorrect (gdb) p /x function () $2 = 0xffffffff # incorrect maybe after spending a few hours debugging you suspect something is wrong with that -1, and do: (gdb) ptype function type = int () and maybe, just maybe, you realize that the function actually returns unsigned long long. And you try to fix it with: (gdb) p /x (unsigned long long) function () $3 = 0xffffffffffffffff # incorrect ... which still produces the wrong result, because GDB simply applied int to unsigned long long conversion. Meaning, it sign-extended the integer that it extracted from the return of the function, to 64-bits. and then maybe, after asking around on IRC, you realize you have to cast the function to a pointer of the right type, and call that. It won't be easy, but after a few missteps, you'll get to it: ..... (gdb) p /x ((unsigned long long(*) ()) function) () $666 = 0x7fffffffffffffff # finally! :-) So to improve on the user experience, this patch does the following (interrelated) things: - makes no-debug-info functions no longer default to "int" as return type. Instead, they're left with NULL/"<unknown return type>" return type. (gdb) ptype getenv type = <unknown return type> () - makes calling a function with unknown return type an error. (gdb) p getenv ("PATH") 'getenv' has unknown return type; cast the call to its declared return type - and then to make it easier to call the function, makes it possible to _only_ cast the return of the function to the right type, instead of having to cast the function to a function pointer: (gdb) p (char *) getenv ("PATH") # now Just Works $3 = 0x7fffffffe7d7 "/usr/local/bin:/"... (gdb) p ((char *(*) (const char *)) getenv) ("PATH") # continues working $4 = 0x7fffffffe7d7 "/usr/local/bin:/"... I.e., it makes GDB default the function's return type to the type of the cast, and the function's parameters to the type of the arguments passed down. After this patch, here's what you'll get for the "unsigned long long" example above: (gdb) p function () 'function' has unknown return type; cast the call to its declared return type (gdb) p /x (unsigned long long) function () $4 = 0x7fffffffffffffff # correct! Note that while with "print" GDB shows the name of the function that has the problem: (gdb) p getenv ("PATH") 'getenv' has unknown return type; cast the call to its declared return type which can by handy in more complicated expressions, "ptype" does not: (gdb) ptype getenv ("PATH") function has unknown return type; cast the call to its declared return type This will be fixed in the next patch. gdb/ChangeLog: 2017-09-04 Pedro Alves <palves@redhat.com> * ada-lang.c (ada_evaluate_subexp) <TYPE_CODE_FUNC>: Don't handle TYPE_GNU_IFUNC specially here. Throw error if return type is unknown. * ada-typeprint.c (print_func_type): Handle functions with unknown return type. * c-typeprint.c (c_type_print_base): Handle functions and methods with unknown return type. * compile/compile-c-symbols.c (convert_symbol_bmsym) <mst_text_gnu_ifunc>: Use nodebug_text_gnu_ifunc_symbol. * compile/compile-c-types.c: Include "objfiles.h". (convert_func): For functions with unknown return type, warn and default to int. * compile/compile-object-run.c (compile_object_run): Adjust call to call_function_by_hand_dummy. * elfread.c (elf_gnu_ifunc_resolve_addr): Adjust call to call_function_by_hand. * eval.c (evaluate_subexp_standard): Adjust calls to call_function_by_hand. Handle functions and methods with unknown return type. Pass expect_type to call_function_by_hand. * f-typeprint.c (f_type_print_base): Handle functions with unknown return type. * gcore.c (call_target_sbrk): Adjust call to call_function_by_hand. * gdbtypes.c (objfile_type): Leave nodebug text symbol with NULL return type instead of int. Make nodebug_text_gnu_ifunc_symbol be an integer address type instead of nodebug. * guile/scm-value.c (gdbscm_value_call): Adjust call to call_function_by_hand. * infcall.c (error_call_unknown_return_type): New function. (call_function_by_hand): New "default_return_type" parameter. Pass it down. (call_function_by_hand_dummy): New "default_return_type" parameter. Use it instead of defaulting to int. If there's no default and the return type is unknown, throw an error. If there's a default return type, and the called function has no debug info, then assume the function is prototyped. * infcall.h (call_function_by_hand, call_function_by_hand_dummy): New "default_return_type" parameter. (error_call_unknown_return_type): New declaration. * linux-fork.c (call_lseek): Cast return type of lseek. (inferior_call_waitpid, checkpoint_command): Adjust calls to call_function_by_hand. * linux-tdep.c (linux_infcall_mmap, linux_infcall_munmap): Adjust calls to call_function_by_hand. * m2-typeprint.c (m2_procedure): Handle functions with unknown return type. * objc-lang.c (lookup_objc_class, lookup_child_selector) (value_nsstring, print_object_command): Adjust calls to call_function_by_hand. * p-typeprint.c (pascal_type_print_varspec_prefix): Handle functions with unknown return type. (pascal_type_print_func_varspec_suffix): New function. (pascal_type_print_varspec_suffix) <TYPE_CODE_FUNC, TYPE_CODE_METHOD>: Use it. * python/py-value.c (valpy_call): Adjust call to call_function_by_hand. * rust-lang.c (rust_evaluate_funcall): Adjust call to call_function_by_hand. * valarith.c (value_x_binop, value_x_unop): Adjust calls to call_function_by_hand. * valops.c (value_allocate_space_in_inferior): Adjust call to call_function_by_hand. * typeprint.c (type_print_unknown_return_type): New function. * typeprint.h (type_print_unknown_return_type): New declaration. gdb/testsuite/ChangeLog: 2017-09-04 Pedro Alves <palves@redhat.com> * gdb.base/break-main-file-remove-fail.exp (test_remove_bp): Cast return type of munmap in infcall. * gdb.base/break-probes.exp: Cast return type of foo in infcall. * gdb.base/checkpoint.exp: Simplify using for loop. Cast return type of ftell in infcall. * gdb.base/dprintf-detach.exp (dprintf_detach_test): Cast return type of getpid in infcall. * gdb.base/infcall-exec.exp: Cast return type of execlp in infcall. * gdb.base/info-os.exp: Cast return type of getpid in infcall. Bail on failure to extract the pid. * gdb.base/nodebug.c: #include <stdint.h>. (multf, multf_noproto, mult, mult_noproto, add8, add8_noproto): New functions. * gdb.base/nodebug.exp (test_call_promotion): New procedure. Change expected output of print/whatis/ptype with functions with no debug info. Test all supported languages. Call test_call_promotion. * gdb.compile/compile.exp: Adjust expected output to expect warning. * gdb.threads/siginfo-threads.exp: Likewise.
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extern struct value *call_function_by_hand (struct value *function,
type *default_return_type,
int nargs,
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struct value **args);
/* Similar to call_function_by_hand and additional call
register_dummy_frame_dtor with DUMMY_DTOR and DUMMY_DTOR_DATA for the
created inferior call dummy frame. */
extern struct value *
Stop assuming no-debug-info functions return int The fact that GDB defaults to assuming that functions return int, when it has no debug info for the function has been a recurring source of user confusion. Recently this came up on the errno pretty printer discussions. Shortly after, it came up again on IRC, with someone wondering why does getenv() in GDB return a negative int: (gdb) p getenv("PATH") $1 = -6185 This question (with s/getenv/random-other-C-runtime-function) is a FAQ on IRC. The reason for the above is: (gdb) p getenv $2 = {<text variable, no debug info>} 0x7ffff7751d80 <getenv> (gdb) ptype getenv type = int () ... which means that GDB truncated the 64-bit pointer that is actually returned from getent to 32-bit, and then sign-extended it: (gdb) p /x -6185 $6 = 0xffffe7d7 The workaround is to cast the function to the right type, like: (gdb) p ((char *(*) (const char *)) getenv) ("PATH") $3 = 0x7fffffffe7d7 "/usr/local/bin:/"... IMO, we should do better than this. I see the "assume-int" issue the same way I see printing bogus values for optimized-out variables instead of "<optimized out>" -- I'd much rather that the debugger tells me "I don't know" and tells me how to fix it than showing me bogus misleading results, making me go around tilting at windmills. If GDB prints a signed integer when you're expecting a pointer or aggregate, you at least have some sense that something is off, but consider the case of the function actually returning a 64-bit integer. For example, compile this without debug info: unsigned long long function () { return 0x7fffffffffffffff; } Currently, with pristine GDB, you get: (gdb) p function () $1 = -1 # incorrect (gdb) p /x function () $2 = 0xffffffff # incorrect maybe after spending a few hours debugging you suspect something is wrong with that -1, and do: (gdb) ptype function type = int () and maybe, just maybe, you realize that the function actually returns unsigned long long. And you try to fix it with: (gdb) p /x (unsigned long long) function () $3 = 0xffffffffffffffff # incorrect ... which still produces the wrong result, because GDB simply applied int to unsigned long long conversion. Meaning, it sign-extended the integer that it extracted from the return of the function, to 64-bits. and then maybe, after asking around on IRC, you realize you have to cast the function to a pointer of the right type, and call that. It won't be easy, but after a few missteps, you'll get to it: ..... (gdb) p /x ((unsigned long long(*) ()) function) () $666 = 0x7fffffffffffffff # finally! :-) So to improve on the user experience, this patch does the following (interrelated) things: - makes no-debug-info functions no longer default to "int" as return type. Instead, they're left with NULL/"<unknown return type>" return type. (gdb) ptype getenv type = <unknown return type> () - makes calling a function with unknown return type an error. (gdb) p getenv ("PATH") 'getenv' has unknown return type; cast the call to its declared return type - and then to make it easier to call the function, makes it possible to _only_ cast the return of the function to the right type, instead of having to cast the function to a function pointer: (gdb) p (char *) getenv ("PATH") # now Just Works $3 = 0x7fffffffe7d7 "/usr/local/bin:/"... (gdb) p ((char *(*) (const char *)) getenv) ("PATH") # continues working $4 = 0x7fffffffe7d7 "/usr/local/bin:/"... I.e., it makes GDB default the function's return type to the type of the cast, and the function's parameters to the type of the arguments passed down. After this patch, here's what you'll get for the "unsigned long long" example above: (gdb) p function () 'function' has unknown return type; cast the call to its declared return type (gdb) p /x (unsigned long long) function () $4 = 0x7fffffffffffffff # correct! Note that while with "print" GDB shows the name of the function that has the problem: (gdb) p getenv ("PATH") 'getenv' has unknown return type; cast the call to its declared return type which can by handy in more complicated expressions, "ptype" does not: (gdb) ptype getenv ("PATH") function has unknown return type; cast the call to its declared return type This will be fixed in the next patch. gdb/ChangeLog: 2017-09-04 Pedro Alves <palves@redhat.com> * ada-lang.c (ada_evaluate_subexp) <TYPE_CODE_FUNC>: Don't handle TYPE_GNU_IFUNC specially here. Throw error if return type is unknown. * ada-typeprint.c (print_func_type): Handle functions with unknown return type. * c-typeprint.c (c_type_print_base): Handle functions and methods with unknown return type. * compile/compile-c-symbols.c (convert_symbol_bmsym) <mst_text_gnu_ifunc>: Use nodebug_text_gnu_ifunc_symbol. * compile/compile-c-types.c: Include "objfiles.h". (convert_func): For functions with unknown return type, warn and default to int. * compile/compile-object-run.c (compile_object_run): Adjust call to call_function_by_hand_dummy. * elfread.c (elf_gnu_ifunc_resolve_addr): Adjust call to call_function_by_hand. * eval.c (evaluate_subexp_standard): Adjust calls to call_function_by_hand. Handle functions and methods with unknown return type. Pass expect_type to call_function_by_hand. * f-typeprint.c (f_type_print_base): Handle functions with unknown return type. * gcore.c (call_target_sbrk): Adjust call to call_function_by_hand. * gdbtypes.c (objfile_type): Leave nodebug text symbol with NULL return type instead of int. Make nodebug_text_gnu_ifunc_symbol be an integer address type instead of nodebug. * guile/scm-value.c (gdbscm_value_call): Adjust call to call_function_by_hand. * infcall.c (error_call_unknown_return_type): New function. (call_function_by_hand): New "default_return_type" parameter. Pass it down. (call_function_by_hand_dummy): New "default_return_type" parameter. Use it instead of defaulting to int. If there's no default and the return type is unknown, throw an error. If there's a default return type, and the called function has no debug info, then assume the function is prototyped. * infcall.h (call_function_by_hand, call_function_by_hand_dummy): New "default_return_type" parameter. (error_call_unknown_return_type): New declaration. * linux-fork.c (call_lseek): Cast return type of lseek. (inferior_call_waitpid, checkpoint_command): Adjust calls to call_function_by_hand. * linux-tdep.c (linux_infcall_mmap, linux_infcall_munmap): Adjust calls to call_function_by_hand. * m2-typeprint.c (m2_procedure): Handle functions with unknown return type. * objc-lang.c (lookup_objc_class, lookup_child_selector) (value_nsstring, print_object_command): Adjust calls to call_function_by_hand. * p-typeprint.c (pascal_type_print_varspec_prefix): Handle functions with unknown return type. (pascal_type_print_func_varspec_suffix): New function. (pascal_type_print_varspec_suffix) <TYPE_CODE_FUNC, TYPE_CODE_METHOD>: Use it. * python/py-value.c (valpy_call): Adjust call to call_function_by_hand. * rust-lang.c (rust_evaluate_funcall): Adjust call to call_function_by_hand. * valarith.c (value_x_binop, value_x_unop): Adjust calls to call_function_by_hand. * valops.c (value_allocate_space_in_inferior): Adjust call to call_function_by_hand. * typeprint.c (type_print_unknown_return_type): New function. * typeprint.h (type_print_unknown_return_type): New declaration. gdb/testsuite/ChangeLog: 2017-09-04 Pedro Alves <palves@redhat.com> * gdb.base/break-main-file-remove-fail.exp (test_remove_bp): Cast return type of munmap in infcall. * gdb.base/break-probes.exp: Cast return type of foo in infcall. * gdb.base/checkpoint.exp: Simplify using for loop. Cast return type of ftell in infcall. * gdb.base/dprintf-detach.exp (dprintf_detach_test): Cast return type of getpid in infcall. * gdb.base/infcall-exec.exp: Cast return type of execlp in infcall. * gdb.base/info-os.exp: Cast return type of getpid in infcall. Bail on failure to extract the pid. * gdb.base/nodebug.c: #include <stdint.h>. (multf, multf_noproto, mult, mult_noproto, add8, add8_noproto): New functions. * gdb.base/nodebug.exp (test_call_promotion): New procedure. Change expected output of print/whatis/ptype with functions with no debug info. Test all supported languages. Call test_call_promotion. * gdb.compile/compile.exp: Adjust expected output to expect warning. * gdb.threads/siginfo-threads.exp: Likewise.
2017-09-04 21:21:13 +02:00
call_function_by_hand_dummy (struct value *function,
type *default_return_type,
int nargs,
struct value **args,
dummy_frame_dtor_ftype *dummy_dtor,
void *dummy_dtor_data);
Stop assuming no-debug-info functions return int The fact that GDB defaults to assuming that functions return int, when it has no debug info for the function has been a recurring source of user confusion. Recently this came up on the errno pretty printer discussions. Shortly after, it came up again on IRC, with someone wondering why does getenv() in GDB return a negative int: (gdb) p getenv("PATH") $1 = -6185 This question (with s/getenv/random-other-C-runtime-function) is a FAQ on IRC. The reason for the above is: (gdb) p getenv $2 = {<text variable, no debug info>} 0x7ffff7751d80 <getenv> (gdb) ptype getenv type = int () ... which means that GDB truncated the 64-bit pointer that is actually returned from getent to 32-bit, and then sign-extended it: (gdb) p /x -6185 $6 = 0xffffe7d7 The workaround is to cast the function to the right type, like: (gdb) p ((char *(*) (const char *)) getenv) ("PATH") $3 = 0x7fffffffe7d7 "/usr/local/bin:/"... IMO, we should do better than this. I see the "assume-int" issue the same way I see printing bogus values for optimized-out variables instead of "<optimized out>" -- I'd much rather that the debugger tells me "I don't know" and tells me how to fix it than showing me bogus misleading results, making me go around tilting at windmills. If GDB prints a signed integer when you're expecting a pointer or aggregate, you at least have some sense that something is off, but consider the case of the function actually returning a 64-bit integer. For example, compile this without debug info: unsigned long long function () { return 0x7fffffffffffffff; } Currently, with pristine GDB, you get: (gdb) p function () $1 = -1 # incorrect (gdb) p /x function () $2 = 0xffffffff # incorrect maybe after spending a few hours debugging you suspect something is wrong with that -1, and do: (gdb) ptype function type = int () and maybe, just maybe, you realize that the function actually returns unsigned long long. And you try to fix it with: (gdb) p /x (unsigned long long) function () $3 = 0xffffffffffffffff # incorrect ... which still produces the wrong result, because GDB simply applied int to unsigned long long conversion. Meaning, it sign-extended the integer that it extracted from the return of the function, to 64-bits. and then maybe, after asking around on IRC, you realize you have to cast the function to a pointer of the right type, and call that. It won't be easy, but after a few missteps, you'll get to it: ..... (gdb) p /x ((unsigned long long(*) ()) function) () $666 = 0x7fffffffffffffff # finally! :-) So to improve on the user experience, this patch does the following (interrelated) things: - makes no-debug-info functions no longer default to "int" as return type. Instead, they're left with NULL/"<unknown return type>" return type. (gdb) ptype getenv type = <unknown return type> () - makes calling a function with unknown return type an error. (gdb) p getenv ("PATH") 'getenv' has unknown return type; cast the call to its declared return type - and then to make it easier to call the function, makes it possible to _only_ cast the return of the function to the right type, instead of having to cast the function to a function pointer: (gdb) p (char *) getenv ("PATH") # now Just Works $3 = 0x7fffffffe7d7 "/usr/local/bin:/"... (gdb) p ((char *(*) (const char *)) getenv) ("PATH") # continues working $4 = 0x7fffffffe7d7 "/usr/local/bin:/"... I.e., it makes GDB default the function's return type to the type of the cast, and the function's parameters to the type of the arguments passed down. After this patch, here's what you'll get for the "unsigned long long" example above: (gdb) p function () 'function' has unknown return type; cast the call to its declared return type (gdb) p /x (unsigned long long) function () $4 = 0x7fffffffffffffff # correct! Note that while with "print" GDB shows the name of the function that has the problem: (gdb) p getenv ("PATH") 'getenv' has unknown return type; cast the call to its declared return type which can by handy in more complicated expressions, "ptype" does not: (gdb) ptype getenv ("PATH") function has unknown return type; cast the call to its declared return type This will be fixed in the next patch. gdb/ChangeLog: 2017-09-04 Pedro Alves <palves@redhat.com> * ada-lang.c (ada_evaluate_subexp) <TYPE_CODE_FUNC>: Don't handle TYPE_GNU_IFUNC specially here. Throw error if return type is unknown. * ada-typeprint.c (print_func_type): Handle functions with unknown return type. * c-typeprint.c (c_type_print_base): Handle functions and methods with unknown return type. * compile/compile-c-symbols.c (convert_symbol_bmsym) <mst_text_gnu_ifunc>: Use nodebug_text_gnu_ifunc_symbol. * compile/compile-c-types.c: Include "objfiles.h". (convert_func): For functions with unknown return type, warn and default to int. * compile/compile-object-run.c (compile_object_run): Adjust call to call_function_by_hand_dummy. * elfread.c (elf_gnu_ifunc_resolve_addr): Adjust call to call_function_by_hand. * eval.c (evaluate_subexp_standard): Adjust calls to call_function_by_hand. Handle functions and methods with unknown return type. Pass expect_type to call_function_by_hand. * f-typeprint.c (f_type_print_base): Handle functions with unknown return type. * gcore.c (call_target_sbrk): Adjust call to call_function_by_hand. * gdbtypes.c (objfile_type): Leave nodebug text symbol with NULL return type instead of int. Make nodebug_text_gnu_ifunc_symbol be an integer address type instead of nodebug. * guile/scm-value.c (gdbscm_value_call): Adjust call to call_function_by_hand. * infcall.c (error_call_unknown_return_type): New function. (call_function_by_hand): New "default_return_type" parameter. Pass it down. (call_function_by_hand_dummy): New "default_return_type" parameter. Use it instead of defaulting to int. If there's no default and the return type is unknown, throw an error. If there's a default return type, and the called function has no debug info, then assume the function is prototyped. * infcall.h (call_function_by_hand, call_function_by_hand_dummy): New "default_return_type" parameter. (error_call_unknown_return_type): New declaration. * linux-fork.c (call_lseek): Cast return type of lseek. (inferior_call_waitpid, checkpoint_command): Adjust calls to call_function_by_hand. * linux-tdep.c (linux_infcall_mmap, linux_infcall_munmap): Adjust calls to call_function_by_hand. * m2-typeprint.c (m2_procedure): Handle functions with unknown return type. * objc-lang.c (lookup_objc_class, lookup_child_selector) (value_nsstring, print_object_command): Adjust calls to call_function_by_hand. * p-typeprint.c (pascal_type_print_varspec_prefix): Handle functions with unknown return type. (pascal_type_print_func_varspec_suffix): New function. (pascal_type_print_varspec_suffix) <TYPE_CODE_FUNC, TYPE_CODE_METHOD>: Use it. * python/py-value.c (valpy_call): Adjust call to call_function_by_hand. * rust-lang.c (rust_evaluate_funcall): Adjust call to call_function_by_hand. * valarith.c (value_x_binop, value_x_unop): Adjust calls to call_function_by_hand. * valops.c (value_allocate_space_in_inferior): Adjust call to call_function_by_hand. * typeprint.c (type_print_unknown_return_type): New function. * typeprint.h (type_print_unknown_return_type): New declaration. gdb/testsuite/ChangeLog: 2017-09-04 Pedro Alves <palves@redhat.com> * gdb.base/break-main-file-remove-fail.exp (test_remove_bp): Cast return type of munmap in infcall. * gdb.base/break-probes.exp: Cast return type of foo in infcall. * gdb.base/checkpoint.exp: Simplify using for loop. Cast return type of ftell in infcall. * gdb.base/dprintf-detach.exp (dprintf_detach_test): Cast return type of getpid in infcall. * gdb.base/infcall-exec.exp: Cast return type of execlp in infcall. * gdb.base/info-os.exp: Cast return type of getpid in infcall. Bail on failure to extract the pid. * gdb.base/nodebug.c: #include <stdint.h>. (multf, multf_noproto, mult, mult_noproto, add8, add8_noproto): New functions. * gdb.base/nodebug.exp (test_call_promotion): New procedure. Change expected output of print/whatis/ptype with functions with no debug info. Test all supported languages. Call test_call_promotion. * gdb.compile/compile.exp: Adjust expected output to expect warning. * gdb.threads/siginfo-threads.exp: Likewise.
2017-09-04 21:21:13 +02:00
/* Throw an error indicating that the user tried to call a function
that has unknown return type. FUNC_NAME is the name of the
function to be included in the error message; may be NULL, in which
case the error message doesn't include a function name. */
extern void error_call_unknown_return_type (const char *func_name);
2003-04-21 18:48:41 +02:00
#endif