The previous patch left GDB with an inconsistency. While with normal
expression evaluation the "unknown return type" error shows the name
of the function that misses debug info:
(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 commit is a step toward fixing it.
The problem is that while evaluating the expression above, we have no
reference to the minimal symbol where we could extract the name from.
This is because the resulting expression tree has no reference to the
minsym at all. During parsing, the type and address of the minsym are
extracted and an UNOP_MEMVAL / UNOP_MEMVAL_TLS operator is generated
(see write_exp_elt_msym). With "set debug expression", here's what
you see:
0 OP_FUNCALL Number of args: 0
3 UNOP_MEMVAL Type @0x565334a51930 (<text variable, no debug info>)
6 OP_LONG Type @0x565334a51c60 (__CORE_ADDR), value 140737345035648 (0x7ffff7751d80)
The "print" case finds the function name, because
call_function_by_hand looks up the function by address again.
However, for "ptype", we don't reach that code, because obviously we
don't really call the function.
Unlike minsym references, references to variables with debug info have
a pointer to the variable's symbol in the expression tree, with
OP_VAR_VALUE:
(gdb) ptype main()
...
0 OP_FUNCALL Number of args: 0
3 OP_VAR_VALUE Block @0x0, symbol @0x559bbbd9b358 (main(int, char**))
...
so I don't see why do minsyms need to be different. So to prepare for
fixing the missing function name issue, this commit adds a new
OP_VAR_MSYM_VALUE operator that mimics OP_VAR_VALUE, except that it's
for minsyms instead of debug symbols. For infcalls, we now get
expressions like these:
0 OP_FUNCALL Number of args: 0
3 OP_VAR_MSYM_VALUE Objfile @0x1e41bf0, msymbol @0x7fffe599b000 (getenv)
In the following patch, we'll make OP_FUNCALL extract the function
name from the symbol stored in OP_VAR_VALUE/OP_VAR_MSYM_VALUE.
OP_VAR_MSYM_VALUE will be used more in a later patch in the series
too.
gdb/ChangeLog:
2017-09-04 Pedro Alves <palves@redhat.com>
* ada-lang.c (resolve_subexp): Handle OP_VAR_MSYM_VALUE.
* ax-gdb.c (gen_msym_var_ref): New function.
(gen_expr): Handle OP_VAR_MSYM_VALUE.
* eval.c (evaluate_var_msym_value): New function.
* eval.c (evaluate_subexp_standard): Handle OP_VAR_MSYM_VALUE.
<OP_FUNCALL>: Extract function name from symbol/minsym and pass it
to call_function_by_hand.
* expprint.c (print_subexp_standard, dump_subexp_body_standard):
Handle OP_VAR_MSYM_VALUE.
(union exp_element) <msymbol>: New field.
* minsyms.h (struct type): Forward declare.
(find_minsym_type_and_address): Declare.
* parse.c (write_exp_elt_msym): New function.
(write_exp_msymbol): Delete, refactored as ...
(find_minsym_type_and_address): ... this new function.
(write_exp_msymbol): Reimplement using OP_VAR_MSYM_VALUE.
(operator_length_standard, operator_check_standard): Handle
OP_VAR_MSYM_VALUE.
* std-operator.def (OP_VAR_MSYM_VALUE): New.
(Ref: https://sourceware.org/ml/gdb/2017-06/msg00048.html)
This patch improves GDB support for function aliases defined with
__attribute__ alias. For example, in the test added by this commit,
there is no reference to "func_alias" in the debug info at all, only
to "func"'s definition:
$ nm ./testsuite/outputs/gdb.base/symbol-alias/symbol-alias | grep " func"
00000000004005ae t func
00000000004005ae T func_alias
$ readelf -w ./testsuite/outputs/gdb.base/symbol-alias/symbol-alias | grep func -B 1 -A 8
<1><db>: Abbrev Number: 5 (DW_TAG_subprogram)
<dc> DW_AT_name : (indirect string, offset: 0x111): func
<e0> DW_AT_decl_file : 1
<e1> DW_AT_decl_line : 27
<e2> DW_AT_prototyped : 1
<e2> DW_AT_type : <0xf8>
<e6> DW_AT_low_pc : 0x4005ae
<ee> DW_AT_high_pc : 0xb
<f6> DW_AT_frame_base : 1 byte block: 9c (DW_OP_call_frame_cfa)
<f8> DW_AT_GNU_all_call_sites: 1
So all GDB knows about "func_alias" is from the minsym (elf symbol):
(gdb) p func_alias
$1 = {<text variable, no debug info>} 0x4005ae <func>
(gdb) ptype func_alias
type = int ()
(gdb) p func
$2 = {struct S *(void)} 0x4005ae <func>
(gdb) ptype func
type = struct S {
int field1;
int field2;
} *(void)
The result is that calling func_alias from the command line produces
incorrect results.
This is similar (though not exactly the same) to the glibc
errno/__errno_location/__GI___errno_location situation. On glibc,
errno is defined like this:
extern int *__errno_location (void);
#define errno (*__errno_location ())
with __GI___errno_location being an internal alias for
__errno_location. On my system's libc (F23), I do see debug info for
__errno_location, in the form of name vs linkage name:
<1><95a5>: Abbrev Number: 18 (DW_TAG_subprogram)
<95a6> DW_AT_external : 1
<95a6> DW_AT_name : (indirect string, offset: 0x2c26): __errno_location
<95aa> DW_AT_decl_file : 1
<95ab> DW_AT_decl_line : 24
<95ac> DW_AT_linkage_name: (indirect string, offset: 0x2c21): __GI___errno_location
<95b0> DW_AT_prototyped : 1
<95b0> DW_AT_type : <0x9206>
<95b4> DW_AT_low_pc : 0x20f40
<95bc> DW_AT_high_pc : 0x11
<95c4> DW_AT_frame_base : 1 byte block: 9c (DW_OP_call_frame_cfa)
<95c6> DW_AT_GNU_all_call_sites: 1
however that doesn't matter in practice, because GDB doesn't record
demangled names anyway, and so we end up with the exact same situation
covered by the testcase.
So the fix is to make the expression parser find a debug symbol for
the same address as the just-found minsym, when a lookup by name
didn't find a debug symbol by name. We now get:
(gdb) p func_alias
$1 = {struct S *(void)} 0x4005ae <func>
(gdb) p __errno_location
$2 = {int *(void)} 0x7ffff6e92830 <__errno_location>
I've made the test exercise variable aliases too, for completeness.
Those already work correctly, because unlike for function aliases, GCC
emits debug information for variable aliases.
Tested on GNU/Linux.
gdb/ChangeLog:
2017-08-21 Pedro Alves <palves@redhat.com>
PR gdb/19487
* c-exp.y (variable production): Handle function aliases.
* minsyms.c (msymbol_is_text): New function.
* minsyms.h (msymbol_is_text): Declare.
* symtab.c (find_function_alias_target): New function.
* symtab.h (find_function_alias_target): Declare.
gdb/testsuite/ChangeLog:
2017-08-21 Pedro Alves <palves@redhat.com>
PR gdb/19487
* gdb.base/symbol-alias.c: New.
* gdb.base/symbol-alias2.c: New.
* gdb.base/symbol-alias.exp: New.
This applies the second part of GDB's End of Year Procedure, which
updates the copyright year range in all of GDB's files.
gdb/ChangeLog:
Update copyright year range in all GDB files.
This changes an "int" to a "bool" in the signature for
minimal_symbol_reader::record_full, and then fixes the callers.
2016-10-21 Tom Tromey <tom@tromey.com>
* minsyms.h (minimal_symbol_reader::record_full): "copy_name" now
a bool.
(record, record_with_info): Update.
* minsyms.c (record): Fix indentation.
(record_full): Fix indentation. Update for type change.
* elfread.c (record_minimal_symbol): "copy_name" now a bool.
(elf_symtab_read): "copy_names" now a bool.
(elf_rel_plt_read, elf_read_minimal_symbols): Update.
This changes minimal_symbol_reader to require the objfile to be
passed to the constructor. The class now records the objfile and
automatically uses it later in "install".
This is a minor cleanup that will come in useful in the next patch.
It is separate from the first patch to keep that one a bit simpler to
understand.
2016-10-21 Tom Tromey <tom@tromey.com>
* xcoffread.c (xcoff_initial_scan): Update.
* mipsread.c (mipscoff_symfile_read): Update.
* minsyms.c (minimal_symbol_reader): Add obj argument.
Initialize member.
(install): Remove objfile argument. Update.
* mdebugread.c (elfmdebug_build_psymtabs): Update.
* machoread.c (macho_symfile_read): Update.
* elfread.c (elf_read_minimal_symbols): Update.
* dbxread.c (dbx_symfile_read): Update.
* coffread.c (coff_symfile_read): Update.
* minsyms.h (minimal_symbol_reader): Add m_objfile member.
(constructor): Add objfile argument.
(minimal_symbol_reader::install): Remove objfile argument.
This patch introduced minimal_symbol_reader, a RAII-based class which
replaces the current make_cleanup_discard_minimal_symbols.
2016-10-21 Tom Tromey <tom@tromey.com>
* xcoffread.c (xcoff_initial_scan): Use
minimal_symbol_reader.
* mipsread.c (mipscoff_symfile_read): Use
minimal_symbol_reader.
* minsyms.h (minimal_symbol_reader): New class.
(init_minimal_symbol_collection)
(make_cleanup_discard_minimal_symbols, install_minimal_symbols):
Don't declare.
* minsyms.c (minimal_symbol_reader): Renamed from
init_minimal_symbol_collection, turned into constructor.
(~minimal_symbol_reader): Renamed from
do_discard_minimal_symbols_cleanup, turned into destructor.
(make_cleanup_discard_minimal_symbols): Remove.
(minimal_symbol_reader::install): Rename form
install_minimal_symbols.
* mdebugread.c (elfmdebug_build_psymtabs): Use
minimal_symbol_reader.
* machoread.c (macho_symfile_read): Use
minimal_symbol_reader.
* elfread.c (elf_read_minimal_symbols): Use
minimal_symbol_reader.
* dbxread.c (dbx_symfile_read): Use minimal_symbol_reader.
* coffread.c (coff_symfile_read): Use
minimal_symbol_reader.
minsyms.h incorrectly claims that a couple of functions call
prim_record_minimal_symbol_full with COPY_NAME=0 -- but actually they
pass 1. Passing 1 is the correct behavior, so this patch fixes the
documentation.
I'm checking this in as obvious.
2014-06-16 Tom Tromey <tromey@redhat.com>
* minsyms.h (prim_record_minimal_symbol)
(prim_record_minimal_symbol_and_info): Update comments.
This removes the runtime offsets from minsyms. Instead, these offsets
will now be applied whenever the minsym's address is computed.
This patch redefines MSYMBOL_VALUE_ADDRESS to actually use the offsets
from the given objfile. Then, it updates all the symbol readers,
changing them so that they do not add in the section offset when
creating the symbol.
This change also lets us remove relocation of minsyms from
objfile_relocate1 and also msymbols_sort.
2014-02-26 Tom Tromey <tromey@redhat.com>
* minsyms.c (msymbols_sort): Remove.
* minsyms.h (msymbols_sort): Remove.
* objfiles.c (objfile_relocate1): Don't relocate minsyms.
* symtab.h (MSYMBOL_VALUE_ADDRESS): Use objfile offsets.
* elfread.c (elf_symtab_read): Don't add section offsets.
* xcoffread.c (record_minimal_symbol): Don't add section offset
to minimal symbol address.
* somread.c (text_offset, data_offset): Remove.
(som_symtab_read): Don't add section offsets to minimal symbol
addresses.
* coff-pe-read.c (add_pe_forwarded_sym, read_pe_exported_syms):
Don't add section offsets to minimal symbols.
* coffread.c (coff_symtab_read): Don't add section offsets
to minimal symbol addresses.
* machoread.c (macho_symtab_add_minsym): Don't add section offset
to minimal symbol addresses.
* mipsread.c (read_alphacoff_dynamic_symtab): Don't add
section offset to minimal symbol addresses.
* mdebugread.c (parse_partial_symbols): Don't add section
offset to minimal symbol addresses.
* dbxread.c (read_dbx_dynamic_symtab): Don't add section
offset to minimal symbol addresses.
This introduces minimal_symbol_upper_bound and changes various bits of
code to use it. Since this function is intimately tied to the
implementation of minimal symbol tables, I believe it belongs in
minsyms.c.
The new function is extracted from find_pc_partial_function_gnu_ifunc.
This isn't a "clean" move because the old function interleaved the
caching and the computation; but this doesn't make sense for the new
code.
2014-02-26 Tom Tromey <tromey@redhat.com>
* blockframe.c (find_pc_partial_function_gnu_ifunc): Use
bound minimal symbols. Move code that knows about minsym
table layout...
* minsyms.c (minimal_symbol_upper_bound): ... here. New
function.
* minsyms.h (minimal_symbol_upper_bound): Declare.
* objc-lang.c (find_objc_msgsend): Use bound minimal symbols,
minimal_symbol_upper_bound.
This is another patch in my ongoing series to "split" objfile to share
more read-only data across inferiors. See
http://sourceware.org/gdb/wiki/ObjfileSplitting
When symbols are finally shared, there will be no back-link from the
symbol to its containing objfile, because there may be more than one
such objfile. So, all such back-links must be removed.
One hidden back-link is the msymbol_objfile function. Since
(eventually) a symbol may appear in more than one objfile, trying to
look up the objfile given just a symbol cannot work.
This patch removes msymbol_objfile in favor of using a bound minimal
symbol. It introduces a new function to make this conversion simpler
in some spots.
The bonus of this patch is that using msymbol_objfile is slower than
simply looking up the owning objfile in the first place.
Built and regtested on x86-64 Fedora 18.
* ada-exp.y (write_var_or_type): Use bound_minimal_symbol.
* ada-lang.c (ada_lookup_simple_minsym): Return
bound_minimal_symbol.
* ada-lang.h (ada_lookup_simple_minsym): Update.
* c-exp.y (variable): Use lookup_bound_minimal_symbol.
* f-exp.y (variable): Use lookup_bound_minimal_symbol.
* go-exp.y (variable): Use lookup_bound_minimal_symbol.
* jv-exp.y (push_expression_name): Use lookup_bound_minimal_symbol.
* m2-exp.y (variable): Use lookup_bound_minimal_symbol.
* minsyms.c (msymbol_objfile): Remove.
(lookup_minimal_symbol_internal): New function, from
lookup_minimal_symbol.
(lookup_minimal_symbol): Rewrite using
lookup_minimal_symbol_internal.
(lookup_bound_minimal_symbol): New function.
* minsyms.h (msymbol_objfile): Remove.
(lookup_bound_minimal_symbol): Declare.
* p-exp.y (variable): Use lookup_bound_minimal_symbol.
* parse.c (write_exp_msymbol): Change parameter to a
bound_minimal_symbol.
(write_dollar_variable): Use lookup_bound_minimal_symbol.
* parser-defs.h (write_exp_msymbol): Update.
* printcmd.c (address_info): Use lookup_bound_minimal_symbol.
* symfile.c (simple_read_overlay_table): Use
lookup_bound_minimal_symbol.
* symtab.c (skip_prologue_sal): Don't use msymbol_objfile.
(search_symbols): Likewise.
(print_msymbol_info): Take a bound_minimal_symbol argument.
(symtab_symbol_info, rbreak_command): Update.
* symtab.h (struct symbol_search) <msymbol>: Change type
to bound_minimal_symbol.
* valops.c (find_function_in_inferior): Use
lookup_bound_minimal_symbol.
* value.c (value_fn_field): Use lookup_bound_minimal_symbol.
Two modifications:
1. The addition of 2013 to the copyright year range for every file;
2. The use of a single year range, instead of potentially multiple
year ranges, as approved by the FSF.
Pedro Alves
Joel Brobecker
Tom Tromey
Tom Tromey
Joel Brobecker