linux-kernel - [PATCH] kallsyms: ignore all local labels prefixed by '.L'

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Date:   Tue,  1 Feb 2022 09:32:57 +0800
From:   Changbin Du <changbin.du@...il.com>
To:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Masahiro Yamada <masahiroy@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org,
        llvm@...ts.linux.dev, Changbin Du <changbin.du@...il.com>
Subject: [PATCH] kallsyms: ignore all local labels prefixed by '.L'

The llvm compiler can generate lots of local labels ('.LBB', '.Ltmpxxx',
'.L__unnamed_xx', etc.). These symbols usually are useless for debugging.
And they might overlap with handwritten symbols.

Before this change, a dumpstack shows a local symbol for epc:
[    0.040341][    T0] Hardware name: riscv-virtio,qemu (DT)
[    0.040376][    T0] epc : .LBB6_14+0x22/0x6a
[    0.040452][    T0]  ra : restore_all+0x12/0x6e

The simple solution is that we can ignore all local labels prefixed by '.L'.
For handwritten symbols which need to be preserved should drop the '.L'
prefix.

After this change, the C defined symbol is shown so we can locate the
problematical code immediately:
[    0.035795][    T0] Hardware name: riscv-virtio,qemu (DT)
[    0.036332][    T0] epc : trace_hardirqs_on+0x54/0x13c
[    0.036567][    T0]  ra : restore_all+0x12/0x6e

Signed-off-by: Changbin Du <changbin.du@...il.com>
---
 scripts/kallsyms.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/scripts/kallsyms.c b/scripts/kallsyms.c
index 54ad86d13784..8caabddf817c 100644
--- a/scripts/kallsyms.c
+++ b/scripts/kallsyms.c
@@ -108,7 +108,7 @@ static bool is_ignored_symbol(const char *name, char type)
 	/* Symbol names that begin with the following are ignored.*/
 	static const char * const ignored_prefixes[] = {
 		"$",			/* local symbols for ARM, MIPS, etc. */
-		".LASANPC",		/* s390 kasan local symbols */
+		".L",			/* local labels, .LBB,.Ltmpxxx,.L__unnamed_xx,.LASANPC, etc. */
 		"__crc_",		/* modversions */
 		"__efistub_",		/* arm64 EFI stub namespace */
 		"__kvm_nvhe_",		/* arm64 non-VHE KVM namespace */
-- 
2.32.0