This would seem like a job for <asm/asm.h>. On January 30, 2014 3:00:28 AM PST, David Woodhouse <[email protected]> wrote: >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. > >Signed-off-by: David Woodhouse <[email protected]> >--- > >Let me know if you'd rather have this as an incremental patch. I would >have preferred checking for BITS_PER_LONG==64 rather than __x86_64__ >but it seems we set that to 64 even when building the 16-bit code. > > 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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