The ptrace args/return types detection doesn't work properly in C++
mode, on non-GNU/Linux hosts. For example, on gcc70 (NetBSD 5.1),
where the prototype is:
int ptrace(int, __pid_t, void*, int);
configure misdetects it as:
$ grep PTRACE_TYPE config.h
#define PTRACE_TYPE_ARG1 int
#define PTRACE_TYPE_ARG3 int *
#define PTRACE_TYPE_ARG4 int
/* #undef PTRACE_TYPE_ARG5 */
#define PTRACE_TYPE_RET int
resulting in:
../../src/gdb/amd64bsd-nat.c: In function 'void amd64bsd_fetch_inferior_registers(target_ops*, regcache*, int)':
../../src/gdb/amd64bsd-nat.c:56: warning: dereferencing type-punned pointer will break strict-aliasing rules
../../src/gdb/amd64bsd-nat.c: In function 'void amd64bsd_store_inferior_registers(target_ops*, regcache*, int)':
../../src/gdb/amd64bsd-nat.c:104: warning: dereferencing type-punned pointer will break strict-aliasing rules
../../src/gdb/amd64bsd-nat.c:110: warning: dereferencing type-punned pointer will break strict-aliasing rules
We could address this [1], however despite ptrace.m4's claim:
# Needs to be tested in C++ mode, to detect whether we need to cast
# the first argument to enum __ptrace_request.
it appears that there's actually no need to test in C++ mode. Always
running the ptrace tests in C mode works just the same on GNU/Linux.
I remember experimenting with several different ways to handle the
original issue back then, and maybe that was needed in some other
attempt and then I didn't realize it ended up not really necessary.
Confirmed that this fixes the NetBSD 5.1 C++ build, and confirmed that
C and C++ builds on Fedora 23 are unaffected.
[1] - https://sourceware.org/ml/gdb-patches/2016-04/msg00374.html
gdb/ChangeLog:
2016-04-18 Pedro Alves <palves@redhat.com>
* ptrace.m4 (GDB_AC_PTRACE): Don't run tests in C++ mode.
* configure: Regenerate.
gdb/gdbserver/ChangeLog:
2016-04-18 Pedro Alves <palves@redhat.com>
* configure: Regenerate.
Building in C++ mode issues ~40 warnings like this:
../../src/gdb/linux-nat.c: In function ‘int linux_handle_extended_wait(lwp_info*, int, int)’:
../../src/gdb/linux-nat.c:2016:51: warning: invalid conversion from ‘int’ to ‘__ptrace_request’ [-fpermissive]
ptrace (PTRACE_GETEVENTMSG, pid, 0, &new_pid);
The issue is that in glibc, ptrace's first parameter is an enum.
That's not a problem if we pick the PTRACE_XXX requests from
sys/ptrace.h, as those will be values of the corresponding enum.
However, we have fallback definitions for PTRACE_XXX symbols when the
system headers miss them (such as PTRACE_GETEVENTMSG above), and those
are plain integer constants. E.g., nat/linux-ptrace.h:
#define PTRACE_GETEVENTMSG 0x4201
One idea would be to fix this by defining those fallbacks like:
-#define PTRACE_GETEVENTMSG 0x4201
+#define PTRACE_GETEVENTMSG ((enum __ptrace_request) 0x4201)
However, while glibc's ptrace uses enum __ptrace_request for first
parameter:
extern long int ptrace (enum __ptrace_request __request, ...) __THROW;
other libc's, like e.g., Android's bionic do not -- in that case, the
first parameter is int:
long ptrace(int request, pid_t pid, void * addr, void * data);
So the fix I came up is to make configure/ptrace.m4 also detect the
type of the ptrace's first parameter and defin PTRACE_TYPE_ARG1, as
already does the for parameters 3-4, and then simply wrap ptrace with
a macro that casts the first argument to the detected type. (I'm
leaving adding a nicer wrapper for when we drop building in C).
While this adds the wrapper, GNU/Linux files won't use it until the
next patch, which makes all native GNU/Linux files include
gdb_ptrace.h.
gdb/ChangeLog:
2015-07-24 Pedro Alves <palves@redhat.com>
* ptrace.m4 (ptrace tests): Test in C++ mode. Try with 'enum
__ptrace_request as first parameter type instead of int.
(PTRACE_TYPE_ARG1): Define.
* nat/gdb_ptrace.h [!PTRACE_TYPE_ARG5] (ptrace): Define as wrapper
that casts first argument to PTRACE_TYPE_ARG1.
* config.in: Regenerate.
* configure: Regenerate.
gdb/gdbserver/ChangeLog:
2015-07-24 Pedro Alves <palves@redhat.com>
* config.in: Regenerate.
* configure: Regenerate.
This factors the ptrace checks out of gdb's configure.ac to a new
ptrace.m4 file, and then makes gdbserver's configure.ac source it too.
gdb/ChangeLog:
2015-07-24 Pedro Alves <palves@redhat.com>
* acinclude.m4: Include ptrace.m4.
* configure.ac: Call GDB_AC_PTRACE and move ptrace checks ...
* ptrace.m4: ... to this new file.
gdb/gdbserver/ChangeLog:
2015-07-24 Pedro Alves <palves@redhat.com>
* acinclude.m4: Include ../ptrace.m4.
* configure.ac: Call GDB_AC_PTRACE.
* config.in, configure: Regenerate.
Pedro Alves