Messages in this thread Patch in this message | | | Date | Tue, 19 May 2020 11:02:26 +0200 | From | Peter Zijlstra <> | Subject | Re: [patch V6 00/37] x86/entry: Rework leftovers and merge plan |
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On Tue, May 19, 2020 at 10:38:26AM +0200, Peter Zijlstra wrote: > $ make CC=gcc-9 O=defconfig-build/ vmlinux -j40 -s > vmlinux.o: warning: objtool: exc_debug()+0x158: call to trace_hwlat_timestamp() leaves .noinstr.text section > vmlinux.o: warning: objtool: exc_nmi()+0x190: call to trace_hwlat_timestamp() leaves .noinstr.text section > vmlinux.o: warning: objtool: do_machine_check()+0x46: call to mce_rdmsrl() leaves .noinstr.text section > $ > > (it really isn't defconfig, but your config-fail + DEBUG_ENTRY) >
With comment on, as requested.
--- diff --git a/arch/x86/include/asm/bug.h b/arch/x86/include/asm/bug.h index f128e5c2ed42..fb34ff641e0a 100644 --- a/arch/x86/include/asm/bug.h +++ b/arch/x86/include/asm/bug.h @@ -79,8 +79,8 @@ do { \ do { \ instrumentation_begin(); \ _BUG_FLAGS(ASM_UD2, BUGFLAG_WARNING|(flags)); \ - instrumentation_end(); \ annotate_reachable(); \ + instrumentation_end(); \ } while (0) #include <asm-generic/bug.h> diff --git a/include/linux/compiler.h b/include/linux/compiler.h index 7db5902f8f6e..4b8fabed46ae 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -120,25 +120,61 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val, /* Annotate a C jump table to allow objtool to follow the code flow */ #define __annotate_jump_table __section(.rodata..c_jump_table) +#ifdef CONFIG_DEBUG_ENTRY /* Begin/end of an instrumentation safe region */ -#define instrumentation_begin() ({ \ +#define instrumentation_begin() ({ \ asm volatile("%c0:\n\t" \ ".pushsection .discard.instr_begin\n\t" \ ".long %c0b - .\n\t" \ ".popsection\n\t" : : "i" (__COUNTER__)); \ }) -#define instrumentation_end() ({ \ - asm volatile("%c0:\n\t" \ +/* + * Because instrumentation_{begin,end}() can nest, objtool validation considers + * _begin() a +1 and _end() a -1 and computes a sum over the instructions. + * When the value is greater than 0, we consider instrumentation allowed. + * + * There is a problem with code like: + * + * noinstr void foo() + * { + * instrumentation_begin(); + * ... + * if (cond) { + * instrumentation_begin(); + * ... + * instrumentation_end(); + * } + * bar(); + * instrumentation_end(); + * } + * + * If instrumentation_end() would be an empty label, like all the other + * annotations, the inner _end(), which is at the end of a conditional block, + * would land on the instruction after the block. + * + * If we then consider the sum of the !cond path, we'll see that the call to + * bar() is with a 0-value, even though, we meant it to happen with a positive + * value. + * + * To avoid this, have _end() be a NOP instruction, this ensures it will be + * part of the condition block and does not escape. + */ +#define instrumentation_end() ({ \ + asm volatile("%c0: nop\n\t" \ ".pushsection .discard.instr_end\n\t" \ ".long %c0b - .\n\t" \ ".popsection\n\t" : : "i" (__COUNTER__)); \ }) +#endif /* CONFIG_DEBUG_ENTRY */ #else #define annotate_reachable() #define annotate_unreachable() #define __annotate_jump_table +#endif + +#ifndef instrumentation_begin #define instrumentation_begin() do { } while(0) #define instrumentation_end() do { } while(0) #endif
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