From: Nadav Amit <namit@vmware.com> To: <linux-kernel@vger.kernel.org>, <x86@kernel.org> Cc: Nadav Amit <namit@vmware.com>, Christopher Li <sparse@chrisli.org>, <linux-sparse@vger.kernel.org> Subject: [PATCH v4 2/9] x86: objtool: use asm macro for better compiler decisions Date: Tue, 12 Jun 2018 04:50:43 -0700 [thread overview] Message-ID: <20180612115050.185112-3-namit@vmware.com> (raw) In-Reply-To: <20180612115050.185112-1-namit@vmware.com> GCC considers the number of statements in inlined assembly blocks, according to new-lines and semicolons, as an indication to the cost of the block in time and space. This data is distorted by the kernel code, which puts information in alternative sections. As a result, the compiler may perform incorrect inlining and branch optimizations. In the case of objtool, this distortion is extreme, since anyhow the annotations of objtool are discarded during linkage. The solution 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. This patch slightly increases the kernel size. text data bss dec hex filename 18140829 10224724 2957312 31322865 1ddf2f1 ./vmlinux before 18140970 10225412 2957312 31323694 1ddf62e ./vmlinux after (+829) Static text symbols: Before: 40321 After: 40302 (-19) Cc: Christopher Li <sparse@chrisli.org> Cc: linux-sparse@vger.kernel.org Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com> Signed-off-by: Nadav Amit <namit@vmware.com> --- 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 <linux/compiler.h> diff --git a/include/linux/compiler.h b/include/linux/compiler.h index ab4711c63601..3efd85334774 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() @@ -280,6 +271,45 @@ unsigned long read_word_at_a_time(const void *addr) #endif /* __KERNEL__ */ +#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 -- 2.17.0
WARNING: multiple messages have this Message-ID (diff)
From: Nadav Amit <namit@vmware.com> To: linux-kernel@vger.kernel.org, x86@kernel.org Cc: Nadav Amit <namit@vmware.com>, Christopher Li <sparse@chrisli.org>, linux-sparse@vger.kernel.org Subject: [PATCH v4 2/9] x86: objtool: use asm macro for better compiler decisions Date: Tue, 12 Jun 2018 04:50:43 -0700 [thread overview] Message-ID: <20180612115050.185112-3-namit@vmware.com> (raw) In-Reply-To: <20180612115050.185112-1-namit@vmware.com> GCC considers the number of statements in inlined assembly blocks, according to new-lines and semicolons, as an indication to the cost of the block in time and space. This data is distorted by the kernel code, which puts information in alternative sections. As a result, the compiler may perform incorrect inlining and branch optimizations. In the case of objtool, this distortion is extreme, since anyhow the annotations of objtool are discarded during linkage. The solution 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. This patch slightly increases the kernel size. text data bss dec hex filename 18140829 10224724 2957312 31322865 1ddf2f1 ./vmlinux before 18140970 10225412 2957312 31323694 1ddf62e ./vmlinux after (+829) Static text symbols: Before: 40321 After: 40302 (-19) Cc: Christopher Li <sparse@chrisli.org> Cc: linux-sparse@vger.kernel.org Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com> Signed-off-by: Nadav Amit <namit@vmware.com> --- 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 <linux/compiler.h> diff --git a/include/linux/compiler.h b/include/linux/compiler.h index ab4711c63601..3efd85334774 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() @@ -280,6 +271,45 @@ unsigned long read_word_at_a_time(const void *addr) #endif /* __KERNEL__ */ +#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 -- 2.17.0
next prev parent reply other threads:[~2018-06-12 19:09 UTC|newest] Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top 2018-06-12 11:50 [PATCH v4 0/9] x86: macrofying inline asm for better compilation Nadav Amit 2018-06-12 11:50 ` [PATCH v4 1/9] Makefile: Prepare for using macros for inline asm Nadav Amit 2018-06-12 11:50 ` Nadav Amit 2018-06-13 17:43 ` Masahiro Yamada 2018-06-13 20:36 ` Sam Ravnborg 2018-06-17 0:47 ` Masahiro Yamada 2018-06-13 22:19 ` Nadav Amit 2018-06-17 0:40 ` Masahiro Yamada 2018-06-19 7:12 ` Nadav Amit 2018-06-12 11:50 ` Nadav Amit [this message] 2018-06-12 11:50 ` [PATCH v4 2/9] x86: objtool: use asm macro for better compiler decisions Nadav Amit 2018-06-12 11:50 ` [PATCH v4 3/9] x86: refcount: prevent gcc distortions Nadav Amit 2018-06-12 11:50 ` [PATCH v4 4/9] x86: alternatives: macrofy locks for better inlining Nadav Amit 2018-06-12 11:50 ` [PATCH v4 5/9] x86: bug: prevent gcc distortions Nadav Amit 2018-06-12 11:50 ` [PATCH v4 6/9] x86: prevent inline distortion by paravirt ops Nadav Amit 2018-06-19 15:09 ` Juergen Gross 2018-06-19 15:09 ` Juergen Gross 2018-06-12 11:50 ` [PATCH v4 7/9] x86: extable: use macros instead of inline assembly Nadav Amit 2018-06-12 11:50 ` [PATCH v4 8/9] x86: cpufeature: " Nadav Amit 2018-06-12 11:50 ` [PATCH v4 9/9] x86: jump-labels: " Nadav Amit
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