[Bug ada/50678] [4.7 Regression] FAIL: c52104y on x86_64-apple-darwin10

[ebotcazou at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50678

--- Comment #23 from Eric Botcazou <ebotcazou at gcc dot gnu.org> 2011-10-12 18:04:00 UTC ---
It turns out that Tom's patch is innocent, you can reproduce the problem at the
preceding revision if you compiled at -O1 instead of -O2.

This appears to be a problem in the signal unwinder on Darwin.  Here's the
status of the registers when the probe hits the guard page:

Program received signal SIGSEGV, Segmentation fault.
0x0000000100002a44 in _ada_c52104y () at c52104y.adb:31
31                          ARRX52  :  TABOX52 ;     -- BIG ARRAY HERE.
(gdb) info reg
rax            0x10000010       268435472
rbx            0x7fff5fbffa40   140734799804992
rcx            0x7fff5f3ffa30   140734791416368
rdx            0xf      15
rsi            0x7fff5fbffa30   140734799804976
rdi            0x7fff4fbfca30   140734531357232
rbp            0x7fff5fbffa80   0x7fff5fbffa80
rsp            0x7fff5fbffa30   0x7fff5fbffa30
r8             0x80000002       2147483650
r9             0x10000000       268435456
r10            0x80000002       2147483650
r11            0x10000001       268435457
r12            0xfffffffffffffffa       -6
r13            0xd      13
r14            0x0      0
r15            0x1      1
rip            0x100002a44      0x100002a44 <_ada_c52104y+416>

And here's the status of the registers when execution resumes:

 Breakpoint 1, 0x0000000100002aa2 in _ada_c52104y () at c52104y.adb:49
49      END C52104Y;
(gdb) info reg
rax            0x100100080      4296016000
rbx            0xf      15
rcx            0x7fff5f3ffa30   140734791416368
rdx            0x1      1
rsi            0x7fff5fbffa30   140734799804976
rdi            0x7fff4fbfca30   140734531357232
rbp            0x7fff5fbffa80   0x7fff5fbffa80
rsp            0x7fff5fbffa30   0x7fff5fbffa30
r8             0x80000002       2147483650
r9             0x10000000       268435456
r10            0x80000002       2147483650
r11            0x10000001       268435457
r12            0xfffffffffffffffa       -6
r13            0xd      13
r14            0x0      0
r15            0x1      1
rip            0x100002aa2      0x100002aa2 <_ada_c52104y+510>


Note how the value of rdx has apparently been moved to rbx; this is the bug,
rbx is a call-saved register so its value is supposed to be preserved here.