From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793971477; b=OLYBtmQ5EUmVVNe5rxDXcmjDR0A0+37Io9Ncgk+aW5jb27UyFOoXuun6VBRHIorU5QAK rngfTx/VlZNHO2JRj4Dw5ziJjXMAgp1wqSunZnC+kUI7h25CydMK6BO0JA99JYEvy5vAH vzUaEn79G0lRWihO3WItHmq5p6Fq4IVes5xyVfellaeIrMbv4aS9kME6NHWMu9mMZc4E0 74I4UuLgwmmgH9EfORBo4hGrMDSSwlgTE0AefJz9aFbtP8mbl4QgbNt4VLRM35Aez6ctk jjrTpSRXD1UluKyWNrs1qVTbO+czEXTXMADZJYFXPyGFXBmh9u83X0UVx994vRZjUxw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793971477; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: MIME-Version:Content-Type:Content-Transfer-Encoding; bh=e43YrtecMjPm4fM2M1xYU97C1oeC1q0OIEyNhmRIcx8=; b=shtIK9Kh4W0hlMhssh2MZA7ZG2w2BV/WF/pCZTQUzj3XjtLS5Ni9xeI+NpAP9jzS+1W7 FB2o6njCDh8aWpFyg7Eu+ve2t+MqoaMUR9DKOeas7lJGsTLI7zqci0iDkaL6sLI4seEOw c221hI3C2A8BYD1C25/Dl1akLxz9EVVexFTgOwO2OmtzrU4n4zvGQnzGWpu9G/DnJ1aBo 1UU6l1VUYw9V0QFc8OJXp6JmtTLN2HXEMv4+33yWuFTtU98xQpUxdXg8H0XNsOH5UcIfL gYfde3Ga24O/BTSrmWmlwyPo5RuZr5dRfJZVyVg6rhGTEZoe8f/vOOFZb4W4xdWZY3g== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=VsC3wqL0; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5AA50606A326; Fri, 6 Nov 2026 13:24:37 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=VsC3wqL0 Received: by smtp.kernel.org (Postfix) with ESMTPSA id EA7A81F0089F; Fri, 6 Nov 2026 13:24:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793971477; bh=e43YrtecMjPm4fM2M1xYU97C1oeC1q0OIEyNhmRIcx8=; h=From:To:Cc:Subject:Date; b=VsC3wqL0xYA9YTVg8Bo0t8wTvf1JPszSs40UrkkMO2q69xxWxVpt/BoSVCDKwSmxu csrhNJezmjjeSvquJMvW9NV6RX0nx1Y5R2sv3P4uS6VeAeSa4F5NVBn6xVicRg7gad B9GnHfUJ+2UBJGNZ3mg4hZLxm7WT0trVZj12x7f3j2UtQCYfbsy/ToIXEooDulflps WeBCWLLXhAWT9dmWb+nckPssPwXXrtzfmDIg+e2cOpkveijyZBmqMdwJLKSGXt5x6P N7WPLQZ/Tb00Nm2tRxGu3etec0iaO4EgCKjomeV6fOzwSSgoCpO+IMfwib7wF9dSDn 6oZOhl0vh6W3A== From: Sasha Levin To: Andrew Morton , Masahiro Yamada , Luis Chamberlain , Linus Torvalds , Richard Weinberger , Juergen Gross , Geert Uytterhoeven , James Bottomley Cc: Sasha Levin , Jonathan Corbet , Nathan Chancellor , Nicolas Schier , Petr Pavlu , Daniel Gomez , Aaron Tomlin , Greg KH , Petr Mladek , Steven Rostedt , Kees Cook , Peter Zijlstra , Thorsten Leemhuis , Vlastimil Babka , Helge Deller , Randy Dunlap , Laurent Pinchart , Vivian Wang , Zhen Lei , Sami Tolvanen , linux-kernel@vger.kernel.org, linux-kbuild@vger.kernel.org, linux-modules@vger.kernel.org, linux-doc@vger.kernel.org Subject: [PATCH v11 0/4] kallsyms: embed source file:line info in kernel stack traces Date: Fri, 6 Nov 2026 08:24:28 -0500 Message-ID: <20261106132432.248387-1-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit CONFIG_KALLSYMS_LINEINFO embeds a compact address-to-line lookup table in the kernel image so stack traces print source locations directly, without decode_stacktrace.sh or a vmlinux with debug info at runtime: default_idle+0x9/0x10 (arch/x86/kernel/process.c:768) default_idle_call+0x6e/0xb0 (kernel/sched/idle.c:122) do_idle+0x38f/0x660 (kernel/sched/idle.c:199) cpu_startup_entry+0x4e/0x60 (kernel/sched/idle.c:453) rest_init+0x277/0x280 (init/main.c:732) common_startup_64+0x13e/0x158 (arch/x86/kernel/head_64.S:418) Patch 2 extends this to loadable modules, patch 3 delta-compresses the tables, patch 4 adds KUnit coverage. Why this is useful ================== A stack trace in a bug report is usually all you get. The reporter has already rebooted, the machine belongs to a customer, or the failure came out of an automated run that tore its environment down an hour ago. What lands in the report is a list of symbol+offset frames: ext4_do_update_inode+0x2a1/0x4c0 ext4_mark_iloc_dirty+0x5f/0x210 __ext4_mark_inode_dirty+0x9c/0x330 Turning that into source locations requires the exact vmlinux that produced it, with debug info, fed to decode_stacktrace.sh or addr2line. In practice that artifact is the thing that is missing: - Distributions strip the shipped kernel and put debug info in a separate package of a few hundred megabytes that is not installed by default. Fetching it after the fact only helps if it still matches the build that crashed, and on a machine that has been updated since, it does not. - A reporter who rebuilds "the same" kernel to decode the trace does not get the same offsets. A different compiler version, one changed config option, or a different link order moves symbols around. The decode then yields plausible but wrong line numbers, which is worse than yielding none, because nothing flags it as wrong. - Panics captured through pstore/ramoops, a serial console, a photograph of a screen, or a customer's ticket system arrive as text. There is no binary left to go back to. The usual answer, "please rebuild with CONFIG_DEBUG_INFO and reproduce", quietly ends a good share of investigations: the reproducer is rare, the machine is in production, or the reporter has moved on. With the table embedded, the trace above decodes itself at the point it is printed, on the machine that crashed, with no second artifact to find. Two cases go beyond convenience, because symbol+offset cannot express them at all: - Inlining. A frame names the outermost function that survived inlining, so an oops inside a static helper or a header inline reports the caller. The offset is the only clue about which inlined body faulted, and it is not a clue anyone can follow without the binary. A file:line points into the header the code actually came from. - Assembly. Frames in .S files have no useful decode in a plain trace; here they resolve like any other, for instance arch/x86/entry/entry_64.S:121. Module frames are the worst case today, since decoding them needs the matching .ko, built with debug info and kept from the build that ran. Patch 2 makes them self-annotating, which matters most for out-of-tree and vendor modules, where the person reading the trace rarely has that. For anyone triaging at scale, syzbot-style pipelines, distribution crash aggregation, kdump fleets, traces that carry file:line can be clustered by source location instead of by symbol+offset, which changes from build to build. The same trace text stays comparable across kernel versions for far longer. The feature is opt-in and bounded. On x86_64 defconfig + CONFIG_DEBUG_INFO the stripped image grows 8.0 MiB (52.2 -> 60.2 MiB, +15.3%) with the compression in 3/4. There is no cost on any hot path: the tables are read-only data, consulted when formatting offset-bearing symbols, with no locks and no allocations, so the lookup is safe from NMI and panic context. Lookups use offsets from _text, so KASLR does not disturb them, and nothing is needed at runtime: no debuginfod, no symbol server, no network. The information all of this rests on already exists at build time. Today it is discarded at the end of the build and asked for again, months later, from whoever hit the bug. This series keeps 8 MiB of it instead. Changes since v10 ================= All from the sashiko.dev review of v10: - Run the second partial link of a module without module.lds, which the first link has already applied. Applying it twice left __start_alloc_tags/__stop_alloc_tags around an empty range, so with CONFIG_MEM_ALLOC_PROFILING loading sit.ko oopsed on a NULL counter, and it emitted the BYTE(0) stub sections of arm and arm64 twice, so no arm64 module loaded at all. - gen_lineinfo: merge entries that share an address before adding symbol-start entries and collapsing repeated lines. Doing both in one pass let a compile unit's line-0 marker displace or cut short another unit's row. Stop copying a line-0 entry to a symbol start, and drop seq_end_between(), which could never return true. - gen_lineinfo --module: start the section bias ranges at 1 GiB and leave a gap after each one. lkdtm.ko keeps code in .rodata, which gets no bias, so its rows read as offsets into .text; and in ppc64's xt_SECMARK.ko the zero-length last row of .text, sitting on its end address, read as offset 0 of .exit.text. Also recount each section's entries on every path through deduplicate(). - KUnit: test_cross_file_inline() failed on arm64, where the inlined header helper compiled to no instruction of its own; the helper now calls into the second object. test_many_lines_mid_function() asserts that it finds an annotated address instead of passing when it finds none, and both function walks compare against the printed symbol name, which has a leading dot on PowerPC ELFv1. Drop test_static_function(), a duplicate, and test_assembly_no_lineinfo(), which could not fail. Fix two stale comments. Also, the Kconfig help in 1/4 now gives the same uncompressed size as the commit message, 16MB instead of 18MB. v10: https://lore.kernel.org/all/20261102111455.919102-1-sashal@kernel.org/ Tool use ======== LLM coding assistants were used throughout this series: for parts of the implementation, for review passes over each version, and to build the DWARF fixtures and checking scripts behind the testing below. Testing ======= v11 on v7.4-rc1: - KUnit under QEMU, x86_64 defconfig + CONFIG_DEBUG_INFO (KVM), arm64 defconfig and arm multi_v7_defconfig + CONFIG_THUMB2_KERNEL (TCG): x86_64 =y 31 passed, 1 skipped x86_64 =m 31 passed, 1 skipped x86_64 =m, CONFIG_KALLSYMS_LINEINFO_MODULES=n 8 passed, 24 skipped x86_64 =m, LLVM=1 31 passed, 1 skipped arm64 =y 31 passed, 1 skipped arm64 =m 31 passed, 1 skipped arm =y 31 passed, 1 skipped No failures. The skips are the module-only test in =y builds and, without module lineinfo, every test that needs it. - arm64: the KUnit module, fuse, cuse, netfs, overlay and the two aes-neon modules load, and SysRq-l frames are annotated, module frames included. - x86_64 with CONFIG_MEM_ALLOC_PROFILING: sit.ko and kvm.ko load and their tags show up in /proc/allocinfo. - Every module of x86_64 (GCC and Clang), i386, arm64, arm (multi_v7_defconfig with ARM_MODULE_PLTS), riscv64, ppc64 and ppc32 builds, 3,621 in all, has the sections, sizes, flags and __start_/__stop_ symbols that v7.4-rc1's single module.lds link gives it, except where it cannot matter: with GNU ld on x86 .note.GNU-stack comes out as SHT_NOTE, and on arm .ARM.attributes is merged with the table object's and each unwind index gains an EXIDX_CANTUNWIND entry for the address just past its last function. - For every build, the table generated from the final vmlinux is the one linked into it, including ppc64, which takes the regeneration pass. - Run on the vmlinux and every module of those builds, gen_lineinfo emits the same tables as v10's except for the fixes above: on ppc64, xt_SECMARK.ko and lkdtm.ko lose the misplaced rows, and the line-0 entries v10 copied onto symbol starts are gone (3 on x86_64, 9 on i386, 1 with Clang, 681 on ppc64), which changes no lookup. The v9 results below therefore still apply to the generator. - Each of the four patches builds standalone with no warnings. A rebuild with nothing changed relinks nothing, and touching scripts/gen_lineinfo.c relinks vmlinux and every module. - x86_64 defconfig built with -ffunction-sections, where sequences of one compile unit sit back to back: KUnit =y 31 passed, 1 skipped, and the vmlinux table is v10's less one line-0 entry. >From v9, on v7.3-rc3 with a distribution-style config: - Every entry of four built modules diffed against addr2line: 100,725 entries agree. 16,098 addresses probed across them in the other two directions: none annotated where DWARF has no location, none left unannotated where it has one - The vmlinux table checked the same three ways: 4,000 sampled entries agree with addr2line, and of 4,001 probed addresses none is wrong in either direction. Repeated on a build with -ffunction-sections, where one compile unit's sequences do end up adjacent, which is the case the row-selection rule for shared addresses turns on - SysRq-l backtraces annotated, including .S frames and header inlines - Every .ko sub-table header 4-byte aligned, 14 modules with a blob, 9 of them with two or more section descriptors - Multi-object coverage checked by dumping the blobs: kvm.ko now names all 30 of its source files, where before it named one - Compressed debug info: -gz=zlib and -gz=zstd objects give tables identical to an uncompressed build - Relinking a module with only LDFLAGS_MODULE changed keeps its table - A module relinked with a stale table object planted in the build tree ignores it and emits the same section, byte for byte - MIPS64, SPARC64 and Hexagon objects checked directly: MIPS64 matches llvm-addr2line, the other two are refused rather than mis-generated - arm64 defconfig, ARCH=arm multi_v7_defconfig (943 modules), ARCH=i386 defconfig, and x86_64 with LLVM=1: all clean, no warnings Sasha Levin (4): kallsyms: embed source file:line info in kernel stack traces kallsyms: extend lineinfo to loadable modules kallsyms: delta-compress lineinfo tables for ~2.7x size reduction kallsyms: add KUnit tests for lineinfo feature Documentation/admin-guide/index.rst | 1 + .../admin-guide/kallsyms-lineinfo.rst | 100 + MAINTAINERS | 9 + include/linux/kallsyms.h | 18 +- include/linux/mod_lineinfo.h | 321 +++ include/linux/module.h | 40 + init/Kconfig | 35 + kernel/kallsyms.c | 110 +- kernel/kallsyms_internal.h | 11 + kernel/module/kallsyms.c | 200 ++ kernel/module/main.c | 26 + lib/Kconfig.debug | 10 + lib/tests/Makefile | 4 + lib/tests/lineinfo_kunit.c | 1087 +++++++ lib/tests/lineinfo_kunit.h | 22 + lib/tests/lineinfo_kunit_second.c | 21 + scripts/.gitignore | 1 + scripts/Makefile | 3 + scripts/Makefile.modfinal | 44 +- scripts/Makefile.vmlinux | 4 + scripts/empty_lineinfo.S | 38 + scripts/gen-mod-lineinfo.sh | 45 + scripts/gen_lineinfo.c | 2532 +++++++++++++++++ scripts/kallsyms.c | 11 + scripts/link-vmlinux.sh | 91 +- 25 files changed, 4772 insertions(+), 12 deletions(-) create mode 100644 Documentation/admin-guide/kallsyms-lineinfo.rst create mode 100644 include/linux/mod_lineinfo.h create mode 100644 lib/tests/lineinfo_kunit.c create mode 100644 lib/tests/lineinfo_kunit.h create mode 100644 lib/tests/lineinfo_kunit_second.c create mode 100644 scripts/empty_lineinfo.S create mode 100755 scripts/gen-mod-lineinfo.sh create mode 100644 scripts/gen_lineinfo.c base-commit: 6628e7d4c6b25c8d18f1345e3a20d21829aae7e4 -- 2.53.0