diff options
| author | Borislav Petkov <bp@suse.de> | 2018-07-14 02:27:01 -0700 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2018-07-17 11:31:44 +0200 |
| commit | 2d45dae0af88a2602e37e596fdc69f66497f3bb0 (patch) | |
| tree | 9efd59da00f13b1a3ebaf0df47cd40f6c24752ef /arch/x86/Kconfig.debug | |
| parent | 7b2330a33983f103327f929189ef9c8f935d9f0c (diff) | |
x86/cpufeature: Replace the old static_cpu_has() with safe variant
commit bc696ca05f5a8927329ec276a892341e006b00ba upstream
So the old one didn't work properly before alternatives had run.
And it was supposed to provide an optimized JMP because the
assumption was that the offset it is jumping to is within a
signed byte and thus a two-byte JMP.
So I did an x86_64 allyesconfig build and dumped all possible
sites where static_cpu_has() was used. The optimization amounted
to all in all 12(!) places where static_cpu_has() had generated
a 2-byte JMP. Which has saved us a whopping 36 bytes!
This clearly is not worth the trouble so we can remove it. The
only place where the optimization might count - in __switch_to()
- we will handle differently. But that's not subject of this
patch.
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1453842730-28463-6-git-send-email-bp@alien8.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Srivatsa S. Bhat <srivatsa@csail.mit.edu>
Reviewed-by: Matt Helsley (VMware) <matt.helsley@gmail.com>
Reviewed-by: Alexey Makhalov <amakhalov@vmware.com>
Reviewed-by: Bo Gan <ganb@vmware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'arch/x86/Kconfig.debug')
| -rw-r--r-- | arch/x86/Kconfig.debug | 10 |
1 files changed, 0 insertions, 10 deletions
diff --git a/arch/x86/Kconfig.debug b/arch/x86/Kconfig.debug index da00fe1f48f4..2aa212fb0faf 100644 --- a/arch/x86/Kconfig.debug +++ b/arch/x86/Kconfig.debug @@ -367,16 +367,6 @@ config DEBUG_IMR_SELFTEST If unsure say N here. -config X86_DEBUG_STATIC_CPU_HAS - bool "Debug alternatives" - depends on DEBUG_KERNEL - ---help--- - This option causes additional code to be generated which - fails if static_cpu_has() is used before alternatives have - run. - - If unsure, say N. - config X86_DEBUG_FPU bool "Debug the x86 FPU code" depends on DEBUG_KERNEL |