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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
commit 9565a349f2
2 changed files with 14 additions and 14 deletions
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8
src/thread/powerpc/clone.s
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@ -16,9 +16,9 @@ __clone:
# in order that the child can find the start func and its arg, we need to store it into
# non-volative regs. to do so, we have to store those 2 regs into our stackframe, so
# we can restore them later.
stw 30, -4(1)
stw 31, -8(1)
subi 1, 1, 16
stw 30, 12(1)
stw 31, 8(1)
# save r3 (func) into r30, and r6(arg) into r31
mr 30, 3
@ -72,9 +72,9 @@ sc
2:
# restore stack
lwz 30, 12(1)
lwz 31, 8(1)
addi 1, 1, 16
lwz 30, -4(1)
lwz 31, -8(1)
blr