From dd3f80c16c4d7767777fc58face6394feb3e38cb Mon Sep 17 00:00:00 2001 From: David Gibson Date: Mon, 15 Feb 2016 22:47:36 +1100 Subject: [PATCH] altstack: Declare memory clobbers altstack includes a couple of inline asm blocks with x86 push and pop instructions. These instructions will access memory (the stack), but that's not declared in inline asm statement. We seem to be getting away with it, but in theory that could allow the compiler to re-order accesses to local variables across the asm block. Since those blocks change the location of the stack, that could be very bad. Adding a "memory" clobber should prevent this (effectively making the asm blocks a compiler memory barrier). Signed-off-by: David Gibson --- ccan/altstack/altstack.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/ccan/altstack/altstack.c b/ccan/altstack/altstack.c index 640344db..63512931 100644 --- a/ccan/altstack/altstack.c +++ b/ccan/altstack/altstack.c @@ -108,9 +108,10 @@ int altstack(rlim_t max, void *(*fn)(void *), void *arg, void **out) "mov %1, %%rsp\n\t" "sub $8, %%rsp\n\t" "push %%r10" - : "=r" (rsp_save_[0]) : "0" (m + max) : "r10"); + : "=r" (rsp_save_[0]) : "0" (m + max) : "r10", "memory"); out_ = fn_(arg_); - asm volatile ("pop %rsp"); + asm volatile ("pop %%rsp" + : : : "memory"); ret = 0; if (out) *out = out_; } -- 2.39.2