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Date: Fri, 4 Aug 2017 00:12:32 -0500
From: Bobby Bingham <koorogi@...rogi.info>
To: musl@...ts.openwall.com
Subject: [PATCH] ppc64: fix setjmp/longjmp handling of TOC pointer
The TOC pointer is constant within a single dso, but needs to be saved
and restored around cross-dso calls. The PLT stub saves it to the
caller's stack frame, and the linker adds code to the caller to restore
it.
With a local call, as within a single dso or with static linking, this
doesn't happen and the TOC pointer is always in r2. Therefore,
setjmp/longjmp need to save/restore the TOC pointer from/to different
locations depending on whether the call to setjmp was a local or non-local
call.
It is always safe for longjmp to restore to both r2 and the caller's stack.
If the call to setjmp was local, and only r2 matters and the stack location
will be ignored, but is required by the ABI to be reserved for the TOC
pointer. If the call was non-local, then only the stack location matters,
and whatever is restored into r2 will be clobbered anyway when the caller
reloads r2 from the stack.
A little extra care is required for sigsetjmp, because it uses setjmp
internally. After the second return from this setjmp call, r2 will contain
the caller's TOC pointer instead of libc's TOC pointer. We need to save
and restore the correct libc pointer before we can tail call to
__sigsetjmp_tail.
---
src/setjmp/powerpc64/longjmp.s | 14 +++++++++-----
src/setjmp/powerpc64/setjmp.s | 21 ++++++++++++++++-----
src/signal/powerpc64/sigsetjmp.s | 21 ++++++++++++++-------
3 files changed, 39 insertions(+), 17 deletions(-)
diff --git a/src/setjmp/powerpc64/longjmp.s b/src/setjmp/powerpc64/longjmp.s
index 7f241c2d..81d45ff6 100644
--- a/src/setjmp/powerpc64/longjmp.s
+++ b/src/setjmp/powerpc64/longjmp.s
@@ -10,10 +10,14 @@ longjmp:
# 1) restore cr
ld 0, 1*8(3)
mtcr 0
- # 2) restore r1-r2 (SP and TOC)
+ # 2) restore SP
ld 1, 2*8(3)
+ # 3) restore TOC into both r2 and the caller's stack.
+ # Which location is required depends on whether setjmp was called
+ # locally or non-locally, but it's always safe to restore to both.
ld 2, 3*8(3)
- # 3) restore r14-r31
+ std 2, 24(1)
+ # 4) restore r14-r31
ld 14, 4*8(3)
ld 15, 5*8(3)
ld 16, 6*8(3)
@@ -32,7 +36,7 @@ longjmp:
ld 29, 19*8(3)
ld 30, 20*8(3)
ld 31, 21*8(3)
- # 4) restore floating point registers f14-f31
+ # 5) restore floating point registers f14-f31
lfd 14, 22*8(3)
lfd 15, 23*8(3)
lfd 16, 24*8(3)
@@ -52,7 +56,7 @@ longjmp:
lfd 30, 38*8(3)
lfd 31, 39*8(3)
- # 5) restore vector registers v20-v31
+ # 6) restore vector registers v20-v31
addi 3, 3, 40*8
lvx 20, 0, 3 ; addi 3, 3, 16
lvx 21, 0, 3 ; addi 3, 3, 16
@@ -67,7 +71,7 @@ longjmp:
lvx 30, 0, 3 ; addi 3, 3, 16
lvx 31, 0, 3
- # 6) return r4 ? r4 : 1
+ # 7) return r4 ? r4 : 1
mr 3, 4
cmpwi cr7, 4, 0
bne cr7, 1f
diff --git a/src/setjmp/powerpc64/setjmp.s b/src/setjmp/powerpc64/setjmp.s
index d16d4bae..37683fda 100644
--- a/src/setjmp/powerpc64/setjmp.s
+++ b/src/setjmp/powerpc64/setjmp.s
@@ -1,24 +1,35 @@
- .global ___setjmp
- .hidden ___setjmp
.global __setjmp
.global _setjmp
.global setjmp
.type __setjmp,@function
.type _setjmp,@function
.type setjmp,@function
-___setjmp:
__setjmp:
_setjmp:
setjmp:
+ ld 5, 24(1) # load from the TOC slot in the caller's stack frame
+ b __setjmp_toc
+
+ .localentry __setjmp,.-__setjmp
+ .localentry _setjmp,.-_setjmp
+ .localentry setjmp,.-setjmp
+ mr 5, 2
+
+ .global __setjmp_toc
+ .hidden __setjmp_toc
+ # same as normal setjmp, except TOC pointer to save is provided in r5.
+ # r4 would normally be the 2nd parameter, but we're using r5 to simplify calling from sigsetjmp.
+ # solves the problem of knowing whether to save the TOC pointer from r2 or the caller's stack frame.
+__setjmp_toc:
# 0) store IP into 0, then into the jmpbuf pointed to by r3 (first arg)
mflr 0
std 0, 0*8(3)
# 1) store cr
mfcr 0
std 0, 1*8(3)
- # 2) store r1-r2 (SP and TOC)
+ # 2) store SP and TOC
std 1, 2*8(3)
- std 2, 3*8(3)
+ std 5, 3*8(3)
# 3) store r14-31
std 14, 4*8(3)
std 15, 5*8(3)
diff --git a/src/signal/powerpc64/sigsetjmp.s b/src/signal/powerpc64/sigsetjmp.s
index 52ac1d03..410c2831 100644
--- a/src/signal/powerpc64/sigsetjmp.s
+++ b/src/signal/powerpc64/sigsetjmp.s
@@ -2,29 +2,36 @@
.global __sigsetjmp
.type sigsetjmp,%function
.type __sigsetjmp,%function
- .hidden ___setjmp
+ .hidden __setjmp_toc
sigsetjmp:
__sigsetjmp:
addis 2, 12, .TOC.-__sigsetjmp@ha
addi 2, 2, .TOC.-__sigsetjmp@l
+ ld 5, 24(1) # load from the TOC slot in the caller's stack frame
+ b 1f
+
.localentry sigsetjmp,.-sigsetjmp
.localentry __sigsetjmp,.-__sigsetjmp
+ mr 5, 2
+1:
cmpwi cr7, 4, 0
- beq- cr7, ___setjmp
+ beq- cr7, __setjmp_toc
- mflr 5
- std 5, 512(3)
- std 16, 512+8+8(3)
+ mflr 6
+ std 6, 512(3)
+ std 2, 512+16(3)
+ std 16, 512+24(3)
mr 16, 3
- bl ___setjmp
+ bl __setjmp_toc
mr 4, 3
mr 3, 16
ld 5, 512(3)
mtlr 5
- ld 16, 512+8+8(3)
+ ld 2, 512+16(3)
+ ld 16, 512+24(3)
.hidden __sigsetjmp_tail
b __sigsetjmp_tail
--
2.13.3
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