Re: [PATCH v3 9/9] compile: compile printf: gdbserver support

[Jan Kratochvil <jan.kratochvil@redhat.com>]

On Sat, 11 Apr 2015 21:44:37 +0200, Jan Kratochvil wrote:
> former patch injects plain:
> 	printf (...);
> This patch injects gdbserver-compatible:
> 	f = open_memstream (&s, ...);
> 	fprintf (f, ...);
> 	fclose (f);
> 	return s;

I have realized this print+printf patchset introduces calling inferior
implicit malloc() + explicit free() (by free_inferior_memory) which the
original 'compile code' series avoided (using gdbarch_infcall_mmap() instead).
The goal was not to crash the inferior futher with print commands when
analyzing corrupted inferior memory lists.

I somehow expected that printf()/fprintf() are so heavyweight they will call
malloc() on their own so this mmap goal is no longer achievable for printf.
But I have found now glibc in most real world cases uses just alloca().

The problem is even calling fmemopen() instead of open_memstream() still
implicitly calls malloc() - for fmemopen_cookie_t and for FILE.

The only idea I have is to redirect by a breakpoint glibc's implicit calls to
malloc() into GDB's allocator by inferior mmap.  But that seems a bit ugly.

So currently keeping it as a known bug.


Jan