linux-kernel - [PATCH] x86, boot: fix word-size assumptions in has

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Date:	Wed, 29 Jan 2014 12:01:37 +0000
From:	David Woodhouse <dwmw2@...radead.org>
To:	Kees Cook <keescook@...omium.org>
Cc:	linux-kernel@...r.kernel.org, x86@...nel.org,
	kernel-hardening@...ts.openwall.com, adurbin@...gle.com,
	Eric Northup <digitaleric@...gle.com>, jln@...gle.com,
	wad@...gle.com, Mathias Krause <minipli@...glemail.com>,
	Zhang Yanfei <zhangyanfei@...fujitsu.com>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: [PATCH] x86, boot: fix word-size assumptions in has_eflag() inline
 asm

Commit dd78b97367bd575918204cc89107c1479d3fc1a7 ("x86, boot: Move CPU
flags out of cpucheck") introduced ambiguous inline asm in the
has_eflag() function. We want the instruction to be 'pushfl', but we
just say 'pushf' and hope the compiler does what we wanted.

When building with 'clang -m16', it won't, because clang doesn't use
the horrid '.code16gcc' hack that even 'gcc -m16' uses internally.

Say what we mean and don't make the compiler make assumptions.

Signed-off-by: David Woodhouse <David.Woodhouse@...el.com>
---
 arch/x86/boot/cpuflags.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/arch/x86/boot/cpuflags.c b/arch/x86/boot/cpuflags.c
index a9fcb7c..168dd25 100644
--- a/arch/x86/boot/cpuflags.c
+++ b/arch/x86/boot/cpuflags.c
@@ -32,16 +32,16 @@ int has_eflag(unsigned long mask)
 {
 	unsigned long f0, f1;
 
-	asm volatile("pushf	\n\t"
-		     "pushf	\n\t"
+	asm volatile("pushfl	\n\t"
+		     "pushfl	\n\t"
 		     "pop %0	\n\t"
 		     "mov %0,%1	\n\t"
 		     "xor %2,%1	\n\t"
 		     "push %1	\n\t"
-		     "popf	\n\t"
-		     "pushf	\n\t"
+		     "popfl	\n\t"
+		     "pushfl	\n\t"
 		     "pop %1	\n\t"
-		     "popf"
+		     "popfl"
 		     : "=&r" (f0), "=&r" (f1)
 		     : "ri" (mask));
 
-- 
1.8.5.3




-- 
dwmw2

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