From c06c4d8090513f2974dfdbed2ac98634357ac475 Mon Sep 17 00:00:00 2001 From: Nadav Amit Date: Wed, 3 Oct 2018 14:30:53 -0700 Subject: [PATCH] x86/objtool: Use asm macros to work around GCC inlining bugs As described in: 77b0bf55bc67: ("kbuild/Makefile: Prepare for using macros in inline assembly code to work around asm() related GCC inlining bugs") GCC's inlining heuristics are broken with common asm() patterns used in kernel code, resulting in the effective disabling of inlining. In the case of objtool the resulting borkage can be significant, since all the annotations of objtool are discarded during linkage and never inlined, yet GCC bogusly considers most functions affected by objtool annotations as 'too large'. The workaround is to set an assembly macro and call it from the inline assembly block. As a result GCC considers the inline assembly block as a single instruction. (Which it isn't, but that's the best we can get.) This increases the kernel size slightly: text data bss dec hex filename 18140829 10224724 2957312 31322865 1ddf2f1 ./vmlinux before 18140970 10225412 2957312 31323694 1ddf62e ./vmlinux after (+829) The number of static text symbols (i.e. non-inlined functions) is reduced: Before: 40321 After: 40302 (-19) [ mingo: Rewrote the changelog. ] Tested-by: Kees Cook Signed-off-by: Nadav Amit Reviewed-by: Josh Poimboeuf Acked-by: Peter Zijlstra (Intel) Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: Christopher Li Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: linux-sparse@vger.kernel.org Link: http://lkml.kernel.org/r/20181003213100.189959-4-namit@vmware.com Signed-off-by: Ingo Molnar --- arch/x86/kernel/macros.S | 2 ++ include/linux/compiler.h | 56 +++++++++++++++++++++++++++++++++++++----------- 2 files changed, 45 insertions(+), 13 deletions(-) diff --git a/arch/x86/kernel/macros.S b/arch/x86/kernel/macros.S index cfc1c7d1a6eb..cee28c3246dc 100644 --- a/arch/x86/kernel/macros.S +++ b/arch/x86/kernel/macros.S @@ -5,3 +5,5 @@ * commonly used. The macros are precompiled into assmebly file which is later * assembled together with each compiled file. */ + +#include diff --git a/include/linux/compiler.h b/include/linux/compiler.h index 681d866efb1e..1921545c6351 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -99,22 +99,13 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val, * unique, to convince GCC not to merge duplicate inline asm statements. */ #define annotate_reachable() ({ \ - asm volatile("%c0:\n\t" \ - ".pushsection .discard.reachable\n\t" \ - ".long %c0b - .\n\t" \ - ".popsection\n\t" : : "i" (__COUNTER__)); \ + asm volatile("ANNOTATE_REACHABLE counter=%c0" \ + : : "i" (__COUNTER__)); \ }) #define annotate_unreachable() ({ \ - asm volatile("%c0:\n\t" \ - ".pushsection .discard.unreachable\n\t" \ - ".long %c0b - .\n\t" \ - ".popsection\n\t" : : "i" (__COUNTER__)); \ + asm volatile("ANNOTATE_UNREACHABLE counter=%c0" \ + : : "i" (__COUNTER__)); \ }) -#define ASM_UNREACHABLE \ - "999:\n\t" \ - ".pushsection .discard.unreachable\n\t" \ - ".long 999b - .\n\t" \ - ".popsection\n\t" #else #define annotate_reachable() #define annotate_unreachable() @@ -299,6 +290,45 @@ static inline void *offset_to_ptr(const int *off) return (void *)((unsigned long)off + *off); } +#else /* __ASSEMBLY__ */ + +#ifdef __KERNEL__ +#ifndef LINKER_SCRIPT + +#ifdef CONFIG_STACK_VALIDATION +.macro ANNOTATE_UNREACHABLE counter:req +\counter: + .pushsection .discard.unreachable + .long \counter\()b -. + .popsection +.endm + +.macro ANNOTATE_REACHABLE counter:req +\counter: + .pushsection .discard.reachable + .long \counter\()b -. + .popsection +.endm + +.macro ASM_UNREACHABLE +999: + .pushsection .discard.unreachable + .long 999b - . + .popsection +.endm +#else /* CONFIG_STACK_VALIDATION */ +.macro ANNOTATE_UNREACHABLE counter:req +.endm + +.macro ANNOTATE_REACHABLE counter:req +.endm + +.macro ASM_UNREACHABLE +.endm +#endif /* CONFIG_STACK_VALIDATION */ + +#endif /* LINKER_SCRIPT */ +#endif /* __KERNEL__ */ #endif /* __ASSEMBLY__ */ #ifndef __optimize -- 2.11.0