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| author | H. Peter Anvin <hpa@zytor.com> | 2010-05-11 17:47:07 -0700 |
|---|---|---|
| committer | H. Peter Anvin <hpa@zytor.com> | 2010-05-11 17:47:07 -0700 |
| commit | a3c8acd04376d604370dcb6cd2143c9c14078a50 (patch) | |
| tree | c6d467d1007ab51fd17b88a37db79d583bac7033 /arch/x86 | |
| parent | dce8bf4e115aa44d590802ce3554e926840c9042 (diff) | |
| download | linux-a3c8acd04376d604370dcb6cd2143c9c14078a50.tar.bz2 | |
x86: Add new static_cpu_has() function using alternatives
For CPU-feature-specific code that touches performance-critical paths,
introduce a static patching version of [boot_]cpu_has(). This is run
at alternatives time and is therefore not appropriate for most
initialization code, but on the other hand initialization code is
generally not performance critical.
On gcc 4.5+ this uses the new "asm goto" feature.
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Suresh Siddha <suresh.b.siddha@intel.com>
LKML-Reference: <1273135546-29690-2-git-send-email-avi@redhat.com>
Diffstat (limited to 'arch/x86')
| -rw-r--r-- | arch/x86/include/asm/cpufeature.h | 57 |
1 files changed, 57 insertions, 0 deletions
diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h index 0cd82d068613..9b11a5cc6662 100644 --- a/arch/x86/include/asm/cpufeature.h +++ b/arch/x86/include/asm/cpufeature.h @@ -175,6 +175,7 @@ #if defined(__KERNEL__) && !defined(__ASSEMBLY__) +#include <asm/asm.h> #include <linux/bitops.h> extern const char * const x86_cap_flags[NCAPINTS*32]; @@ -283,6 +284,62 @@ extern const char * const x86_power_flags[32]; #endif /* CONFIG_X86_64 */ +/* + * Static testing of CPU features. Used the same as boot_cpu_has(). + * These are only valid after alternatives have run, but will statically + * patch the target code for additional performance. + * + */ +static __always_inline __pure bool __static_cpu_has(u8 bit) +{ +#if __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 5) + asm goto("1: jmp %l[t_no]\n" + "2:\n" + ".section .altinstructions,\"a\"\n" + _ASM_ALIGN "\n" + _ASM_PTR "1b\n" + _ASM_PTR "0\n" /* no replacement */ + " .byte %P0\n" /* feature bit */ + " .byte 2b - 1b\n" /* source len */ + " .byte 0\n" /* replacement len */ + " .byte 0xff + 0 - (2b-1b)\n" /* padding */ + ".previous\n" + : : "i" (bit) : : t_no); + return true; + t_no: + return false; +#else + u8 flag; + /* Open-coded due to __stringify() in ALTERNATIVE() */ + asm volatile("1: movb $0,%0\n" + "2:\n" + ".section .altinstructions,\"a\"\n" + _ASM_ALIGN "\n" + _ASM_PTR "1b\n" + _ASM_PTR "3f\n" + " .byte %P1\n" /* feature bit */ + " .byte 2b - 1b\n" /* source len */ + " .byte 4f - 3f\n" /* replacement len */ + " .byte 0xff + (4f-3f) - (2b-1b)\n" /* padding */ + ".previous\n" + ".section .altinstr_replacement,\"ax\"\n" + "3: movb $1,%0\n" + "4:\n" + ".previous\n" + : "=qm" (flag) : "i" (bit)); + return flag; +#endif +} + +#define static_cpu_has(bit) \ +( \ + __builtin_constant_p(boot_cpu_has(bit)) ? \ + boot_cpu_has(bit) : \ + (__builtin_constant_p(bit) && !((bit) & ~0xff)) ? \ + __static_cpu_has(bit) : \ + boot_cpu_has(bit) \ +) + #endif /* defined(__KERNEL__) && !defined(__ASSEMBLY__) */ #endif /* _ASM_X86_CPUFEATURE_H */ |