[Bug libgcc/108727] gcc.dg/split-5.c fails on power 9 BE

["linkw at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108727

Kewen Lin <linkw at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |amodra at gcc dot gnu.org,
                   |                            |amodra at gmail dot com,
                   |                            |segher at gcc dot gnu.org

--- Comment #2 from Kewen Lin <linkw at gcc dot gnu.org> ---
This is one bug in libgcc morestack support (powerpc64 elfv1 ABI specific):

The segfault happens on:

Dump of assembler code for function 00000000.plt_call._Unwind_Resume:
=> 0x0000000010003580 <+0>:     std     r2,40(r1)
   0x0000000010003584 <+4>:     ld      r12,-31760(r2)
   0x0000000010003588 <+8>:     mtctr   r12
   0x000000001000358c <+12>:    ld      r2,-31752(r2)
   0x0000000010003590 <+16>:    cmpldi  r2,0
   0x0000000010003594 <+20>:    bnectr+
   0x0000000010003598 <+24>:    b       0x100031a4 <_Unwind_Resume@plt>
   0x000000001000359c <+28>:    .long 0x0

The target address of std at 0x0000000010003580 is 0x7ffff72e0008, which isn't
writable as the following mappings:

   0x7ffff40f0000     0x7ffff72e0000  0x31f0000        0x0  rw-p
   0x7ffff72e0000     0x7ffff72f0000    0x10000        0x0  ---p

For the stack segment returned from __generic_morestack, we adjust it by 32
bytes:

   bl JUMP_TARGET(__generic_morestack)

   # Start using new stack
   stdu %r29,-32(%r3)           # back-chain
   mr %r1,%r3

but it isn't enough for powerpc64 elfv1 ABI as the TOC base save slot is with
offset 40.

The fix can be to use PARAMS like:

diff --git a/libgcc/config/rs6000/morestack.S
b/libgcc/config/rs6000/morestack.S
index 5e7ad133303..f2fea6abb10 100644
--- a/libgcc/config/rs6000/morestack.S
+++ b/libgcc/config/rs6000/morestack.S
@@ -205,12 +205,12 @@ ENTRY0(__morestack)
         bl JUMP_TARGET(__generic_morestack)

 # Start using new stack
-        stdu %r29,-32(%r3)              # back-chain
+        stdu %r29,-PARAMS(%r3)          # back-chain
         mr %r1,%r3

 # Set __private_ss stack guard for the new stack.
         ld %r12,NEWSTACKSIZE_SAVE(%r29) # modified size
-        addi %r3,%r3,BACKOFF-32
+        addi %r3,%r3,BACKOFF-PARAMS
         sub %r3,%r3,%r12
 # Note that a signal frame has $pc pointing at the instruction
 # where the signal occurred.  For something like a timer

============================================================

Hi Alan, does the above fix look reasonable to you?