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Commit 5fbbc25a authored by David Woodhouse's avatar David Woodhouse Committed by H. Peter Anvin
Browse files

x86, boot: Fix word-size assumptions in has_eflag() inline asm 



Commit dd78b973 ("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: default avatarDavid Woodhouse <David.Woodhouse@intel.com>
Link: http://lkml.kernel.org/r/1391079628.26079.82.camel@shinybook.infradead.org


Signed-off-by: default avatarH. Peter Anvin <hpa@linux.intel.com>
parent 4064e0ea

arch/x86/boot/cpuflags.c

+20 −5
Original line number Diff line number Diff line
@@ -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));