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@intel.com>
Link: http://lkml.kernel.org/r/1391079628.26079.82.camel@shinybook.infradead.org
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

diff --git a/arch/x86/boot/cpuflags.c b/arch/x86/boot/cpuflags.c
index a9fcb7cfb2411fb64034f14dd1185b3b263eac2a..431fa5f84537d1f8019ac2f23c4c01e0573ab955 100644 (file)
--- 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));