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fix powerpc asm not to store data in volatile space below stack pointer

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it's essential to decrement the stack pointer before writing to new
stack space, rather than afterwards. otherwise there is a race
condition during which asynchronous code (signals) could clobber the
data being stored.

it may be possible to optimize the code further using stwu, but I
wanted to avoid making any changes to the actual stack layout in this
commit. further improvements can be made separately if desired.
This commit is contained in:
Rich Felker
2012-11-18 22:57:32 -05:00
parent 0004ea613a
commit 9565a349f2
2 changed files with 14 additions and 14 deletions
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20
src/signal/powerpc/sigsetjmp.s
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@@ -10,25 +10,25 @@ sigsetjmp:
#2) if its 0, goto setjmp code
beq- cr7, 1f
#3) else: we must call pthread_sigmask(SIG_SETMASK, 0, (sigset_t *)buf->__ss);
# thus store r3 on the stack, to restore it later
stw 3, -4(1)
# store old link reg
mflr 0
stw 0, -8(1)
# increase stack frame by 16
subi 1, 1, 16
# thus store r3 on the stack, to restore it later
stw 3, 12(1)
# store old link reg
mflr 0
stw 0, 8(1)
# put pointer to ss buf into r5 (3rd arg)
addi 5, 3, 260
# put "2" i.e. SIG_SETMASK in r3
li 3, 2
li 4, 0
bl pthread_sigmask
#restore r3
lwz 3, 12(1)
#restore link reg
lwz 0, 8(1)
mtlr 0
#restore sp
addi 1, 1, 16
#restore r3
lwz 3, -4(1)
#restore link reg
lwz 0, -8(1)
mtlr 0
1:
b setjmp