From 15b83b69ca99d97643075776ba94f2dd1f05b46e Mon Sep 17 00:00:00 2001
From: Kewen Lin <linkw@linux.ibm.com>
Date: Wed, 8 Mar 2023 00:57:21 -0600
Subject: [PATCH] libgcc, rs6000: Fix bump size for powerpc64 elfv1 ABI
[PR108727]
As PR108727 shows, when cleanup code called by the stack
unwinder calls function _Unwind_Resume, it goes via plt
stub like:
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>
It wants to save TOC base (r2) to r1 + 40, but we only
bump the stack segment by 32 bytes as follows:
stdu %r29,-32(%r3)
It means the access is out of the stack segment allocated
by __generic_morestack, once the touch area isn't writable
like this failure shows, it would cause segment fault.
So fix the bump size with one reasonable value PARAMS.
PR libgcc/108727
libgcc/ChangeLog:
* config/rs6000/morestack.S (__morestack): Use PARAMS for new stack
bump size.
---
libgcc/config/rs6000/morestack.S | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/libgcc/config/rs6000/morestack.S b/libgcc/config/rs6000/morestack.S
index 5e7ad133303c..f2fea6abb105 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
--
GitLab