On Wed, Jan 10, 2007 at 04:32:48PM -0700, Greg Watson wrote:
> If the following code is compiled with 'gcc -g -O0 -o test test.c',
> the address of argc is passed into func() in the ecx register. Since
> ecx is not preserved after the call to printf(), the address of argc
> is corrupted on return from func(). Normally this would not be a
> problem, since argc is never used in the code.
This is a typical problem. There is not much that can be done about
it, although I remember once hearing a proposal that GCC should
forcibly extend the live ranges of local variables (or at least
arguments) at -O0 to improve debugging. That seems sensible to me.
> However, when run under gdb, commands that view the stack frame
> produce strange results, and some commands (e.g. -var-update)
> actually crash the debugger.
A crash is always a bug.
> Breakpoint 1, main (argc=1, argv=0xbffcef14) at test.c:14
> 12 func(&argc);
> (gdb) n
> in func
> 14 printf("hello\n");
> (gdb) where
> #0 main (argc=Cannot access memory at address 0x4
> ) at test.c:16
And honestly, I have no idea how that happened. Does it happen
with a current GDB? I suspect from the error message that this
one is not too recent.
--
Daniel Jacobowitz
CodeSourcery
