From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752827AbeEOV3r (ORCPT ); Tue, 15 May 2018 17:29:47 -0400 Received: from ex13-edg-ou-001.vmware.com ([208.91.0.189]:48538 "EHLO EX13-EDG-OU-001.vmware.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752537AbeEOV0M (ORCPT ); Tue, 15 May 2018 17:26:12 -0400 From: Nadav Amit To: CC: , Nadav Amit , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , , Peter Zijlstra , Josh Poimboeuf Subject: [RFC 2/8] x86: bug: prevent gcc distortions Date: Tue, 15 May 2018 07:11:09 -0700 Message-ID: <20180515141124.84254-3-namit@vmware.com> X-Mailer: git-send-email 2.17.0 In-Reply-To: <20180515141124.84254-1-namit@vmware.com> References: <20180515141124.84254-1-namit@vmware.com> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. The solution is to set an assembly macro and call it from the inlinedv assembly block. As a result GCC considers the inline assembly block as a single instruction. This patch increases the kernel size: text data bss dec hex filename 18126824 10067268 2936832 31130924 1db052c ./vmlinux before 18127205 10068388 2936832 31132425 1db0b09 ./vmlinux after (+1501) But enables more aggressive inlining (and probably branch decisions). The number of static text symbols in vmlinux is lower. Before: 40015 After: 39860 (-155) Cc: Thomas Gleixner Cc: Ingo Molnar Cc: "H. Peter Anvin" Cc: x86@kernel.org Cc: Peter Zijlstra Cc: Josh Poimboeuf Signed-off-by: Nadav Amit --- arch/x86/include/asm/bug.h | 48 +++++++++++++++++++++++--------------- 1 file changed, 29 insertions(+), 19 deletions(-) diff --git a/arch/x86/include/asm/bug.h b/arch/x86/include/asm/bug.h index 6804d6642767..a2d981beb6cb 100644 --- a/arch/x86/include/asm/bug.h +++ b/arch/x86/include/asm/bug.h @@ -30,33 +30,43 @@ #ifdef CONFIG_DEBUG_BUGVERBOSE -#define _BUG_FLAGS(ins, flags) \ +asm("\n" + ".macro __BUG_FLAGS ins:req file:req line:req flags:req size:req\n" + "1:\t \\ins\n\t" + ".pushsection __bug_table,\"aw\"\n" + "2:\t "__BUG_REL(1b) "\t# bug_entry::bug_addr\n\t" + __BUG_REL(\\file) "\t# bug_entry::file\n\t" + ".word \\line" "\t# bug_entry::line\n\t" + ".word \\flags" "\t# bug_entry::flags\n\t" + ".org 2b+\\size\n\t" + ".popsection\n" + ".endm"); + +#define _BUG_FLAGS(ins, flags) \ do { \ - asm volatile("1:\t" ins "\n" \ - ".pushsection __bug_table,\"aw\"\n" \ - "2:\t" __BUG_REL(1b) "\t# bug_entry::bug_addr\n" \ - "\t" __BUG_REL(%c0) "\t# bug_entry::file\n" \ - "\t.word %c1" "\t# bug_entry::line\n" \ - "\t.word %c2" "\t# bug_entry::flags\n" \ - "\t.org 2b+%c3\n" \ - ".popsection" \ - : : "i" (__FILE__), "i" (__LINE__), \ - "i" (flags), \ + asm volatile("__BUG_FLAGS \"" ins "\" %c0 %c1 %c2 %c3" \ + : : "i" (__FILE__), "i" (__LINE__), \ + "i" (flags), \ "i" (sizeof(struct bug_entry))); \ } while (0) #else /* !CONFIG_DEBUG_BUGVERBOSE */ +asm("\n" + ".macro __BUG_FLAGS ins:req flags:req size:req\n" + "1:\t \\ins\n\t" + ".pushsection __bug_table,\"aw\"\n" + "2:\t" __BUG_REL(1b) "\t# bug_entry::bug_addr\n\t" + ".word \\flags" "\t# bug_entry::flags\n\t" + ".org 2b+\\size\n\t" + ".popsection\n" + ".endm"); + #define _BUG_FLAGS(ins, flags) \ do { \ - asm volatile("1:\t" ins "\n" \ - ".pushsection __bug_table,\"aw\"\n" \ - "2:\t" __BUG_REL(1b) "\t# bug_entry::bug_addr\n" \ - "\t.word %c0" "\t# bug_entry::flags\n" \ - "\t.org 2b+%c1\n" \ - ".popsection" \ - : : "i" (flags), \ - "i" (sizeof(struct bug_entry))); \ + asm volatile("__BUG_FLAGS \"" ins "\" %c0 %c1" \ + : : "i" (flags), \ + "i" (sizeof(struct bug_entry))); \ } while (0) #endif /* CONFIG_DEBUG_BUGVERBOSE */ -- 2.17.0