Messages in this thread |  | | | Date | Fri, 29 Oct 2010 16:03:19 -0400 | | From | Mathieu Desnoyers <> | | Subject | Re: [PATCH 6/7] x86, ftrace: Use safe noops, drop trap test |
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* Steven Rostedt (rostedt@goodmis.org) wrote: > From: H. Peter Anvin <hpa@zytor.com> > > Always use a safe 5-byte noop sequence. Drop the trap test, since it > is known to return false negatives on some virtualization platforms on > 32 bits. The resulting code is both simpler and safer. > > Cc: Daniel Drake <dsd@laptop.org> > Cc: Jason Baron <jbaron@redhat.com> > Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Looks good to me.
Acked-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
> Signed-off-by: H. Peter Anvin <hpa@zytor.com> > Signed-off-by: Steven Rostedt <rostedt@goodmis.org> > --- > arch/x86/kernel/alternative.c | 69 +++++++++-------------------------------- > 1 files changed, 15 insertions(+), 54 deletions(-) > > diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c > index a36bb90..0b30214 100644 > --- a/arch/x86/kernel/alternative.c > +++ b/arch/x86/kernel/alternative.c > @@ -644,65 +644,26 @@ void *__kprobes text_poke_smp(void *addr, const void *opcode, size_t len) > > #if defined(CONFIG_DYNAMIC_FTRACE) || defined(HAVE_JUMP_LABEL) > > -unsigned char ideal_nop5[IDEAL_NOP_SIZE_5]; > +#ifdef CONFIG_X86_64 > +unsigned char ideal_nop5[5] = { 0x66, 0x66, 0x66, 0x66, 0x90 }; > +#else > +unsigned char ideal_nop5[5] = { 0x3e, 0x8d, 0x74, 0x26, 0x00 }; > +#endif > > void __init arch_init_ideal_nop5(void) > { > - extern const unsigned char ftrace_test_p6nop[]; > - extern const unsigned char ftrace_test_nop5[]; > - extern const unsigned char ftrace_test_jmp[]; > - int faulted = 0; > - > /* > - * There is no good nop for all x86 archs. > - * We will default to using the P6_NOP5, but first we > - * will test to make sure that the nop will actually > - * work on this CPU. If it faults, we will then > - * go to a lesser efficient 5 byte nop. If that fails > - * we then just use a jmp as our nop. This isn't the most > - * efficient nop, but we can not use a multi part nop > - * since we would then risk being preempted in the middle > - * of that nop, and if we enabled tracing then, it might > - * cause a system crash. > + * There is no good nop for all x86 archs. This selection > + * algorithm should be unified with the one in find_nop_table(), > + * but this should be good enough for now. > * > - * TODO: check the cpuid to determine the best nop. > + * For cases other than the ones below, use the safe (as in > + * always functional) defaults above. > */ > - asm volatile ( > - "ftrace_test_jmp:" > - "jmp ftrace_test_p6nop\n" > - "nop\n" > - "nop\n" > - "nop\n" /* 2 byte jmp + 3 bytes */ > - "ftrace_test_p6nop:" > - P6_NOP5 > - "jmp 1f\n" > - "ftrace_test_nop5:" > - ".byte 0x66,0x66,0x66,0x66,0x90\n" > - "1:" > - ".section .fixup, \"ax\"\n" > - "2: movl $1, %0\n" > - " jmp ftrace_test_nop5\n" > - "3: movl $2, %0\n" > - " jmp 1b\n" > - ".previous\n" > - _ASM_EXTABLE(ftrace_test_p6nop, 2b) > - _ASM_EXTABLE(ftrace_test_nop5, 3b) > - : "=r"(faulted) : "0" (faulted)); > - > - switch (faulted) { > - case 0: > - pr_info("converting mcount calls to 0f 1f 44 00 00\n"); > - memcpy(ideal_nop5, ftrace_test_p6nop, IDEAL_NOP_SIZE_5); > - break; > - case 1: > - pr_info("converting mcount calls to 66 66 66 66 90\n"); > - memcpy(ideal_nop5, ftrace_test_nop5, IDEAL_NOP_SIZE_5); > - break; > - case 2: > - pr_info("converting mcount calls to jmp . + 5\n"); > - memcpy(ideal_nop5, ftrace_test_jmp, IDEAL_NOP_SIZE_5); > - break; > - } > - > +#ifdef CONFIG_X86_64 > + /* Don't use these on 32 bits due to broken virtualizers */ > + if (boot_cpu_data.x86_vendor == X86_VENDOR_INTEL) > + memcpy(ideal_nop5, p6_nops[5], 5); > +#endif > } > #endif > -- > 1.7.1 > >
-- Mathieu Desnoyers Operating System Efficiency R&D Consultant EfficiOS Inc. http://www.efficios.com
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