| Message ID | 20250315-kbuild-prefix-map-v2-1-00e1983b2a23@weissschuh.net (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [v2] kbuild: make all file references relative to source root | expand |
On Sat, Mar 15, 2025 at 10:20 PM Thomas Weißschuh <linux@weissschuh.net> wrote: > > -fmacro-prefix-map only affects __FILE__ and __BASE_FILE__. > Other references, for example in debug information, are not affected. > This makes handling of file references in the compiler outputs harder to > use and creates problems for reproducible builds. > > Switch to -ffile-prefix map which affects all references. > > Also drop the documentation section advising manual specification of > -fdebug-prefix-map for reproducible builds, as it is not necessary > anymore. > > Suggested-by: Ben Hutchings <ben@decadent.org.uk> > Link: https://lore.kernel.org/lkml/c49cc967294f9a3a4a34f69b6a8727a6d3959ed8.camel@decadent.org.uk/ > Acked-by: Borislav Petkov (AMD) <bp@alien8.de> # arch/x86/ > Signed-off-by: Thomas Weißschuh <linux@weissschuh.net> > --- > Changes in v2: > - Pick up Ack from Borislav > - Merge all changes into single patch > - Also drop link to KCFLAGS from docs > - Link to v1: https://lore.kernel.org/r/20250313-kbuild-prefix-map-v1-0-38cea8448c5f@weissschuh.net > --- Applied to linux-kbuild. Thanks. -- Best Regards Masahiro Yamada
On Sat, 2025-03-15 at 14:20 +0100, Thomas Weißschuh wrote: > -fmacro-prefix-map only affects __FILE__ and __BASE_FILE__. > Other references, for example in debug information, are not affected. > This makes handling of file references in the compiler outputs harder to > use and creates problems for reproducible builds. > > Switch to -ffile-prefix map which affects all references. This appears to cover all the C sources, but not quite all the assembly sources: [...] > --- a/arch/x86/boot/Makefile > +++ b/arch/x86/boot/Makefile > @@ -54,7 +54,7 @@ targets += cpustr.h > > KBUILD_CFLAGS := $(REALMODE_CFLAGS) -D_SETUP > KBUILD_AFLAGS := $(KBUILD_CFLAGS) -D__ASSEMBLY__ > -KBUILD_CFLAGS += $(call cc-option,-fmacro-prefix-map=$(srctree)/=) > +KBUILD_CFLAGS += $(call cc-option,-ffile-prefix-map=$(srctree)/=) [...] I think this addition to KBUILD_CFLAGS needs to be done before the assignment to KBUILD_AFLAGS. Also, in some older versions of gcc the -ffile-prefix-map option didn't affect assembly sources - gas only understands --debug-prefix-map and gcc did not do the necessary conversion. But this works properly since at least gcc 12, so I wouldn't worry too much about it. Ben.
On Sun, Mar 16, 2025 at 08:08:37PM +0100, Ben Hutchings wrote: > On Sat, 2025-03-15 at 14:20 +0100, Thomas Weißschuh wrote: > > -fmacro-prefix-map only affects __FILE__ and __BASE_FILE__. > > Other references, for example in debug information, are not affected. > > This makes handling of file references in the compiler outputs harder to > > use and creates problems for reproducible builds. > > > > Switch to -ffile-prefix map which affects all references. > > This appears to cover all the C sources, but not quite all the assembly > sources: > > [...] > > > --- a/arch/x86/boot/Makefile > > +++ b/arch/x86/boot/Makefile > > @@ -54,7 +54,7 @@ targets += cpustr.h > > > > KBUILD_CFLAGS := $(REALMODE_CFLAGS) -D_SETUP > > KBUILD_AFLAGS := $(KBUILD_CFLAGS) -D__ASSEMBLY__ > > -KBUILD_CFLAGS += $(call cc-option,-fmacro-prefix-map=$(srctree)/=) > > +KBUILD_CFLAGS += $(call cc-option,-ffile-prefix-map=$(srctree)/=) > [...] > > I think this addition to KBUILD_CFLAGS needs to be done before the > assignment to KBUILD_AFLAGS. This probably belongs in KBUILD_CPPFLAGS then, similar to clang's '--target' flag and other options that we always want invoked? Cheers, Nathan
diff --git a/Documentation/kbuild/reproducible-builds.rst b/Documentation/kbuild/reproducible-builds.rst index f2dcc39044e66ddd165646e0b51ccb0209aca7dd..a7762486c93fcd3eba08b836bed622a41e829e41 100644 --- a/Documentation/kbuild/reproducible-builds.rst +++ b/Documentation/kbuild/reproducible-builds.rst @@ -46,21 +46,6 @@ The kernel embeds the building user and host names in `KBUILD_BUILD_USER and KBUILD_BUILD_HOST`_ variables. If you are building from a git commit, you could use its committer address. -Absolute filenames ------------------- - -When the kernel is built out-of-tree, debug information may include -absolute filenames for the source files. This must be overridden by -including the ``-fdebug-prefix-map`` option in the `KCFLAGS`_ variable. - -Depending on the compiler used, the ``__FILE__`` macro may also expand -to an absolute filename in an out-of-tree build. Kbuild automatically -uses the ``-fmacro-prefix-map`` option to prevent this, if it is -supported. - -The Reproducible Builds web site has more information about these -`prefix-map options`_. - Generated files in source packages ---------------------------------- @@ -131,7 +116,5 @@ See ``scripts/setlocalversion`` for details. .. _KBUILD_BUILD_TIMESTAMP: kbuild.html#kbuild-build-timestamp .. _KBUILD_BUILD_USER and KBUILD_BUILD_HOST: kbuild.html#kbuild-build-user-kbuild-build-host -.. _KCFLAGS: kbuild.html#kcflags -.. _prefix-map options: https://reproducible-builds.org/docs/build-path/ .. _Reproducible Builds project: https://reproducible-builds.org/ .. _SOURCE_DATE_EPOCH: https://reproducible-builds.org/docs/source-date-epoch/ diff --git a/Makefile b/Makefile index 5c333682dc9142b1aacfe454a5c77f5923554b7d..4f920187cee658ae4d1b807fca365f6994274828 100644 --- a/Makefile +++ b/Makefile @@ -1067,7 +1067,7 @@ endif # change __FILE__ to the relative path to the source directory ifdef building_out_of_srctree -KBUILD_CPPFLAGS += $(call cc-option,-fmacro-prefix-map=$(srcroot)/=) +KBUILD_CPPFLAGS += $(call cc-option,-ffile-prefix-map=$(srcroot)/=) KBUILD_RUSTFLAGS += --remap-path-prefix=$(srcroot)/= endif diff --git a/arch/x86/boot/Makefile b/arch/x86/boot/Makefile index 9cc0ff6e9067d574488a35573eff4d0f8449e398..f500f82864aae80deb74faa3df9a8b6333d6c4ca 100644 --- a/arch/x86/boot/Makefile +++ b/arch/x86/boot/Makefile @@ -54,7 +54,7 @@ targets += cpustr.h KBUILD_CFLAGS := $(REALMODE_CFLAGS) -D_SETUP KBUILD_AFLAGS := $(KBUILD_CFLAGS) -D__ASSEMBLY__ -KBUILD_CFLAGS += $(call cc-option,-fmacro-prefix-map=$(srctree)/=) +KBUILD_CFLAGS += $(call cc-option,-ffile-prefix-map=$(srctree)/=) KBUILD_CFLAGS += -fno-asynchronous-unwind-tables KBUILD_CFLAGS += $(CONFIG_CC_IMPLICIT_FALLTHROUGH) diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile index 5edee7a9786c67e13c295473751b82387bcbd67e..ad324978b2e5b1b6f8be82647769c99db8257ac7 100644 --- a/arch/x86/boot/compressed/Makefile +++ b/arch/x86/boot/compressed/Makefile @@ -38,7 +38,7 @@ KBUILD_CFLAGS += -fno-stack-protector KBUILD_CFLAGS += $(call cc-disable-warning, address-of-packed-member) KBUILD_CFLAGS += $(call cc-disable-warning, gnu) KBUILD_CFLAGS += -Wno-pointer-sign -KBUILD_CFLAGS += $(call cc-option,-fmacro-prefix-map=$(srctree)/=) +KBUILD_CFLAGS += $(call cc-option,-ffile-prefix-map=$(srctree)/=) KBUILD_CFLAGS += -fno-asynchronous-unwind-tables KBUILD_CFLAGS += -D__DISABLE_EXPORTS # Disable relocation relaxation in case the link is not PIE.