Re: SEGV on display /i $pc with i386 target

[Mark Kettenis <kettenis@chello.nl>]

Christopher Faylor <cgf@redhat.com> writes:

> I just noticed a SEGV whenever I do a 'display /i $pc' on cygwin.
> 
> I tried building a gdb for linux to see what was going wrong on
> cygwin but it isn't much better:
> 
> (top-gdb) display /i $pc
> 1: x/i $(null)  0x8072f42 <main+6>:     push   $0x6
> 
> The problem comes from the fact that, while gdb understands that
> $pc == $eip, it doesn't seem to know how to rename $pc to $eip
> when it is outputting the register name.  You can get the same
> behavior by doing something like 'display /i $ps', too (even
> if that doesn't make sense it shouldn't SEGV).

Hmm, this defenitely used to work in the past.  Does anybody have an
idea what broke it?

> The simplest way to fix this is to extend the i386_register_names array
> to include builtin register names, however, maybe the right way to fix
> this is to add something to builtin-reg.c.

I suspect this problem isn't i386-specific, so extending
i386_register_names seems to be the wrong approach to me.

> I noticed that i386_register_names seems to have 41 elements while
> the sum of NUM_REGS + NUM_PSEUDO_REGS == 40.  Is that intentional?

Sort of.  In the current situation, Depending on whether your target
supports the SSE registers NUM_REGS will be either 32 or 41.  Since
NUM_PSEUDO_REGS is 6, and 32 + 6 = 40.

Perhaps this is a good moment to warn you about an implication of
multi-arching the i386 for Cygwin: the Cygwin targets don't support
SSE anymor, since we use the "Unknown" OS/ABI for Cygwin right now.  I
doubt whether this is what you want.  You probably want to introduce
some sort of Cygwin or Win32 OS/ABI that includes those registers.

Mark