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

[Christopher Faylor <cgf@redhat.com>]

On Fri, Aug 30, 2002 at 12:40:10AM +0200, Mark Kettenis wrote:
>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?

I tested cygwin releases that I generated all the way back to April and
saw that, while there were no SEGVs on cygwin, I was getting bogus
output where I saw something like $xmmi used rather than $eib in the
display.

Maybe Andrew's 2002-08-13 change to i386_register_name may have stopped
that from occuring and, essentially, stopped masking some broken
behavior.

>>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 agree.

>> 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.

I noticed that while I was poking at this.  I'll put this on my
long todo list.

cgf