Re: [PATCH] Fix PPC scan_prologue for code generated with -mno-update

[Mark Kettenis <mark.kettenis@xs4all.nl>]

> From: Fred Fish <fnf@specifix.com>
> Date: Thu, 15 Feb 2007 18:07:06 -0700
> 
> If the PPC gcc is used with the -mno-update option, it generates a
> prologue instruction to allocate cache that gdb does not recognize.
> Gdb disassembles it as "addi r1,r1,NUM".
> 
> If you run the gdb testsuite for powerpc-eabi and add -mno-update to
> the list of compilation options, you get a huge increase in failures,
> most due to problems doing backtraces.  Without using -mno-update
> you get:
> 
>   # of expected passes          36024
>   # of unexpected failures      756
> 
> With -mno-update you get:
> 
>   # of expected passes          33220
>   # of unexpected failures      3928
> 
> After applying the attached patch, the results with -mno-update
> become:
> 
>   # of expected passes          36028
>   # of unexpected failures      752
> 
> This also fixes an existing failure (1 for each multilib):
> 
>   4448c4446
>   < FAIL: gdb.base/recurse.exp: next over b = 0 in second instance
>   ---
>   > PASS: gdb.base/recurse.exp: next over b = 0 in second instance
> 
> I didn't examine why that failure was fixed by the patch.

Looks reasonable to me.  However there's one thing I don't understand.
Presuming you're using DWARF2 debug info, why does improving the
prologue scanner make such a big difference?

Mark