Commit-ID: 5fbbc25a99d680feca99a3095f0440f65d4307cc
Gitweb: http://git.kernel.org/tip/5fbbc25a99d680feca99a3095f0440f65d4307cc
Author: David Woodhouse <dwmw2@xxxxxxxxxxxxx>
AuthorDate: Thu, 30 Jan 2014 11:00:28 +0000
Committer: H. Peter Anvin <hpa@xxxxxxxxxxxxxxx>
CommitDate: Thu, 30 Jan 2014 08:04:32 -0800
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. In 16-bit mode 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.
[ hpa: ideally we would be able to use the gcc %zN construct here, but
that is broken for 64-bit integers in gcc < 4.5.
The code with plain "pushf/popf" is fine for 32- or 64-bit mode, but
not for 16-bit mode; in 16-bit mode those are 16-bit instructions in
.code16 mode, and 32-bit instructions in .code16gcc mode. ]
Signed-off-by: David Woodhouse <David.Woodhouse@xxxxxxxxx>
Link: http://lkml.kernel.org/r/1391079628.26079.82.camel@xxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: H. Peter Anvin <hpa@xxxxxxxxxxxxxxx>
---
arch/x86/boot/cpuflags.c | 25 ++++++++++++++++++++-----
1 file changed, 20 insertions(+), 5 deletions(-)
diff --git a/arch/x86/boot/cpuflags.c b/arch/x86/boot/cpuflags.c
index a9fcb7c..431fa5f 100644
--- a/arch/x86/boot/cpuflags.c
+++ b/arch/x86/boot/cpuflags.c
@@ -28,20 +28,35 @@ static int has_fpu(void)
return fsw == 0 && (fcw & 0x103f) == 0x003f;
}
+/*
+ * For building the 16-bit code we want to explicitly specify 32-bit
+ * push/pop operations, rather than just saying 'pushf' or 'popf' and
+ * letting the compiler choose. But this is also included from the
+ * compressed/ directory where it may be 64-bit code, and thus needs
+ * to be 'pushfq' or 'popfq' in that case.
+ */
+#ifdef __x86_64__
+#define PUSHF "pushfq"
+#define POPF "popfq"
+#else
+#define PUSHF "pushfl"
+#define POPF "popfl"
+#endif
+
int has_eflag(unsigned long mask)
{
unsigned long f0, f1;
- asm volatile("pushf \n\t"
- "pushf \n\t"
+ asm volatile(PUSHF " \n\t"
+ PUSHF " \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"
+ POPF " \n\t"
+ PUSHF " \n\t"
"pop %1 \n\t"
- "popf"
+ POPF
: "=&r" (f0), "=&r" (f1)
: "ri" (mask));
--
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