From a7c699d090a1f3795c3271c2b399230e182db06e Mon Sep 17 00:00:00 2001
From: Uday Shankar <ushankar@purestorage.com>
Date: Mon, 31 Mar 2025 16:46:32 -0600
Subject: kbuild: rpm-pkg: build a debuginfo RPM
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 <blk_op_str+40>
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 <ushankar@purestorage.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
---
scripts/package/kernel.spec | 46 +++++++++++++++++++++++++++++++++++++++++++--
scripts/package/mkspec | 10 ++++++++++
2 files changed, 54 insertions(+), 2 deletions(-)
diff --git a/scripts/package/kernel.spec b/scripts/package/kernel.spec
index ac3e5ac01d8a..726f34e11960 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 4dc1466dfc81..c7375bfc25a9 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<<EOF
%define ARCH ${ARCH}
%define KERNELRELEASE ${KERNELRELEASE}
--
cgit v1.2.3