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Mon, 31 Mar 2025 15:46:51 -0700 (PDT) Received: from c7-smtp-2023.dev.purestorage.com ([208.88.159.128]) by smtp-relay.gmail.com with ESMTPS id d9443c01a7336-2291eec553csm6147055ad.14.2025.03.31.15.46.51 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 31 Mar 2025 15:46:51 -0700 (PDT) X-Relaying-Domain: purestorage.com Received: from dev-ushankar.dev.purestorage.com (dev-ushankar.dev.purestorage.com [10.7.70.36]) by c7-smtp-2023.dev.purestorage.com (Postfix) with ESMTP id AF928340235; Mon, 31 Mar 2025 16:46:50 -0600 (MDT) Received: by dev-ushankar.dev.purestorage.com (Postfix, from userid 1557716368) id A45EEE41615; Mon, 31 Mar 2025 16:46:50 -0600 (MDT) From: Uday Shankar Date: Mon, 31 Mar 2025 16:46:32 -0600 Subject: [PATCH v2] kbuild: rpm-pkg: build a debuginfo RPM Precedence: bulk X-Mailing-List: linux-kbuild@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Message-Id: <20250331-debuginfo-v2-1-fb460999a5b3@purestorage.com> X-B4-Tracking: v=1; b=H4sIAEcb62cC/03MQQ6CMBCF4auQWVvTDqLAynsYFoVOyyykpJVGQ 7i7hbhw+U/mfStECkwR2mKFQIkj+ykHngoYRj05EmxyA0qsJMpGGOoXx5P1YjClaS7qpi0qyP9 zIMvvw3p0uUeOLx8+B53Ufv0pSv4pSQkpymttqa9qbFDf5yXQvtSOzoN/Qrdt2xedCqpaqAAAA A== X-Change-ID: 20250209-debuginfo-cd3d9417af21 To: Masahiro Yamada , Nathan Chancellor , Nicolas Schier Cc: linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org, Uday Shankar X-Mailer: b4 0.14.2 The rpm-pkg make target currently suffers from a few issues related to debuginfo: 1. debuginfo for things built into the kernel (vmlinux) is not available in any RPM produced by make rpm-pkg. This makes using tools like systemtap against a make rpm-pkg kernel impossible. 2. debug source for the kernel is not available. This means that commands like 'disas /s' in gdb, which display source intermixed with assembly, can only print file names/line numbers which then must be painstakingly resolved to actual source in a separate editor. 3. debuginfo for modules is available, but it remains bundled with the .ko files that contain module code, in the main kernel RPM. This is a waste of space for users who do not need to debug the kernel (i.e. most users). Address all of these issues by additionally building a debuginfo RPM when the kernel configuration allows for it, in line with standard patterns followed by RPM distributors. With these changes: 1. systemtap now works (when these changes are backported to 6.11, since systemtap lags a bit behind in compatibility), as verified by the following simple test script: # stap -e 'probe kernel.function("do_sys_open").call { printf("%s\n", $$parms); }' dfd=0xffffffffffffff9c filename=0x7fe18800b160 flags=0x88800 mode=0x0 ... 2. disas /s works correctly in gdb, with source and disassembly interspersed: # gdb vmlinux --batch -ex 'disas /s blk_op_str' Dump of assembler code for function blk_op_str: block/blk-core.c: 125 { 0xffffffff814c8740 <+0>: endbr64 127 128 if (op < ARRAY_SIZE(blk_op_name) && blk_op_name[op]) 0xffffffff814c8744 <+4>: mov $0xffffffff824a7378,%rax 0xffffffff814c874b <+11>: cmp $0x23,%edi 0xffffffff814c874e <+14>: ja 0xffffffff814c8768 0xffffffff814c8750 <+16>: mov %edi,%edi 126 const char *op_str = "UNKNOWN"; 0xffffffff814c8752 <+18>: mov $0xffffffff824a7378,%rdx 127 128 if (op < ARRAY_SIZE(blk_op_name) && blk_op_name[op]) 0xffffffff814c8759 <+25>: mov -0x7dfa0160(,%rdi,8),%rax 126 const char *op_str = "UNKNOWN"; 0xffffffff814c8761 <+33>: test %rax,%rax 0xffffffff814c8764 <+36>: cmove %rdx,%rax 129 op_str = blk_op_name[op]; 130 131 return op_str; 132 } 0xffffffff814c8768 <+40>: jmp 0xffffffff81d01360 <__x86_return_thunk> End of assembler dump. 3. The size of the main kernel package goes down substantially, especially if many modules are built (quite typical). Here is a comparison of installed size of the kernel package (configured with allmodconfig, dwarf4 debuginfo, and module compression turned off) before and after this patch: # rpm -qi kernel-6.13* | grep -E '^(Version|Size)' Version : 6.13.0postpatch+ Size : 1382874089 Version : 6.13.0prepatch+ Size : 17870795887 This is a ~92% size reduction. Note that a debuginfo package can only be produced if the following configs are set: - CONFIG_DEBUG_INFO=y - CONFIG_MODULE_COMPRESS=n - CONFIG_DEBUG_INFO_SPLIT=n The first of these is obvious - we can't produce debuginfo if the build does not generate it. The second two requirements can in principle be removed, but doing so is difficult with the current approach, which uses a generic rpmbuild script find-debuginfo.sh that processes all packaged executables. If we want to remove those requirements the best path forward is likely to add some debuginfo extraction/installation logic to the modules_install target (controllable by flags). That way, it's easier to operate on modules before they're compressed, and the logic can be reused by all packaging targets. Signed-off-by: Uday Shankar --- Changes in v2: - Check config requirements more explicitly (Masahiro Yamada) - Ensure modules stay non-executable (Masahiro Yamada) - Always combine debuginfo and debugsource package - Link to v1: https://lore.kernel.org/r/20250210-debuginfo-v1-0-368feb58292a@purestorage.com --- scripts/package/kernel.spec | 46 +++++++++++++++++++++++++++++++++++++++++++-- scripts/package/mkspec | 10 ++++++++++ 2 files changed, 54 insertions(+), 2 deletions(-) --- base-commit: 2c8725c1dca3de043670b38592b1b43105322496 change-id: 20250209-debuginfo-cd3d9417af21 Best regards, diff --git a/scripts/package/kernel.spec b/scripts/package/kernel.spec index ac3e5ac01d8a4daa031bc9e70b792a68f74c388b..726f34e1196018165adf350933a5f816faeeef0b 100644 --- a/scripts/package/kernel.spec +++ b/scripts/package/kernel.spec @@ -2,8 +2,6 @@ %{!?_arch: %define _arch dummy} %{!?make: %define make make} %define makeflags %{?_smp_mflags} ARCH=%{ARCH} -%define __spec_install_post /usr/lib/rpm/brp-compress || : -%define debug_package %{nil} Name: kernel Summary: The Linux Kernel @@ -46,6 +44,36 @@ This package provides kernel headers and makefiles sufficient to build modules against the %{version} kernel package. %endif +%if %{with_debuginfo} +# list of debuginfo-related options taken from distribution kernel.spec +# files +%undefine _include_minidebuginfo +%undefine _find_debuginfo_dwz_opts +%undefine _unique_build_ids +%undefine _unique_debug_names +%undefine _unique_debug_srcs +%undefine _debugsource_packages +%undefine _debuginfo_subpackages +%global _find_debuginfo_opts -r +%global _missing_build_ids_terminate_build 1 +%global _no_recompute_build_ids 1 +%{debug_package} +%endif +# some (but not all) versions of rpmbuild emit %%debug_package with +# %%install. since we've already emitted it manually, that would cause +# a package redefinition error. ensure that doesn't happen +%define debug_package %{nil} + +# later, we make all modules executable so that find-debuginfo.sh strips +# them up. but they don't actually need to be executable, so remove the +# executable bit, taking care to do it _after_ find-debuginfo.sh has run +%define __spec_install_post \ + %{?__debug_package:%{__debug_install_post}} \ + %{__arch_install_post} \ + %{__os_install_post} \ + find %{buildroot}/lib/modules/%{KERNELRELEASE} -name "*.ko" -type f \\\ + | xargs --no-run-if-empty chmod u-x + %prep %setup -q -n linux cp %{SOURCE1} .config @@ -89,8 +117,22 @@ ln -fns /usr/src/kernels/%{KERNELRELEASE} %{buildroot}/lib/modules/%{KERNELRELEA echo "%exclude /lib/modules/%{KERNELRELEASE}/build" } > %{buildroot}/kernel.list +# make modules executable so that find-debuginfo.sh strips them. this +# will be undone later in %%__spec_install_post +find %{buildroot}/lib/modules/%{KERNELRELEASE} -name "*.ko" -type f \ + | xargs --no-run-if-empty chmod u+x + +%if %{with_debuginfo} +# copying vmlinux directly to the debug directory means it will not get +# stripped (but its source paths will still be collected + fixed up) +mkdir -p %{buildroot}/usr/lib/debug/lib/modules/%{KERNELRELEASE} +cp vmlinux %{buildroot}/usr/lib/debug/lib/modules/%{KERNELRELEASE} +%endif + %clean rm -rf %{buildroot} +rm -f debugfiles.list debuglinks.list debugsourcefiles.list debugsources.list \ + elfbins.list %post if [ -x /usr/bin/kernel-install ]; then diff --git a/scripts/package/mkspec b/scripts/package/mkspec index 4dc1466dfc815c110eb7206f83dd874b17f5170f..c7375bfc25a9ad3ae98c088273bd76375ea6962e 100755 --- a/scripts/package/mkspec +++ b/scripts/package/mkspec @@ -23,6 +23,16 @@ else echo '%define with_devel 0' fi +# debuginfo package generation uses find-debuginfo.sh under the hood, +# which only works on uncompressed modules that contain debuginfo +if grep -q CONFIG_DEBUG_INFO=y include/config/auto.conf && + (! grep -q CONFIG_MODULE_COMPRESS=y include/config/auto.conf) && + (! grep -q CONFIG_DEBUG_INFO_SPLIT=y include/config/auto.conf); then +echo '%define with_debuginfo %{?_without_debuginfo: 0} %{?!_without_debuginfo: 1}' +else +echo '%define with_debuginfo 0' +fi + cat<