| Message ID | 20210402123959.5143-1-alobakin@pm.me (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | kbuild: merge module sections under CONFIG_LD_DEAD_CODE_DATA_ELIMINATION too | expand |
On Fri, Apr 2, 2021 at 5:40 AM Alexander Lobakin <alobakin@pm.me> wrote: > > When building with CONFIG_LD_DEAD_CODE_DATA_ELIMINATION, > -fdata-sections and -ffunction-sections are being enabled by the > top-level Makefile, and module section merging is also needed. > Expand the ifdef (and the comment block) to cover that case too. > > Fixes: 6a3193cdd5e5 ("kbuild: lto: Merge module sections if and only if CONFIG_LTO_CLANG is enabled") Wouldn't this trigger the ld.bfd bug described in the commit message when LD_DEAD_CODE_DATA_ELIMINATION is enabled? LTO_CLANG always uses LLD, so it won't have this issue. Sami
On Friday, 2 April 2021, 18:09, Sami Tolvanen <samitolvanen@google.com> wrote: > On Fri, Apr 2, 2021 at 5:40 AM Alexander Lobakin alobakin@pm.me wrote: > > > When building with CONFIG_LD_DEAD_CODE_DATA_ELIMINATION, > > -fdata-sections and -ffunction-sections are being enabled by the > > top-level Makefile, and module section merging is also needed. > > Expand the ifdef (and the comment block) to cover that case too. > > Fixes: 6a3193cdd5e5 ("kbuild: lto: Merge module sections if and only if CONFIG_LTO_CLANG is enabled") > > Wouldn't this trigger the ld.bfd bug described in the commit message > when LD_DEAD_CODE_DATA_ELIMINATION is enabled? LTO_CLANG always uses > LLD, so it won't have this issue. LD_DEAD_CODE_DATA_ELIMINATION is marked “EXPERIMENTAL“ in the config prompt, and arches have to opt-in HAS_LD_DEAD_CODE_DATA_ELIMINATION to give an access to it (only a few does). This should be relatively safe. > Sami Thanks, Al
On Tue, Apr 6, 2021 at 11:42 PM Alexander Lobakin <alobakin@pm.me> wrote: > > On Friday, 2 April 2021, 18:09, Sami > Tolvanen <samitolvanen@google.com> wrote: > > > On Fri, Apr 2, 2021 at 5:40 AM Alexander Lobakin alobakin@pm.me wrote: > > > > > When building with CONFIG_LD_DEAD_CODE_DATA_ELIMINATION, > > > -fdata-sections and -ffunction-sections are being enabled by the > > > top-level Makefile, and module section merging is also needed. > > > Expand the ifdef (and the comment block) to cover that case too. > > > Fixes: 6a3193cdd5e5 ("kbuild: lto: Merge module sections if and only if CONFIG_LTO_CLANG is enabled") Did you test this patch before submission? See the top Makefile closely: ifdef CONFIG_LD_DEAD_CODE_DATA_ELIMINATION KBUILD_CFLAGS_KERNEL += -ffunction-sections -fdata-sections LDFLAGS_vmlinux += --gc-sections endif -ffunction-sections -fdata-sections are passed to only built-in objects, but not to module objects in the first place. KBUILD_CFLAGS_KERNEL is only passed to built-in objects. The situation you claimed never happens. > > Wouldn't this trigger the ld.bfd bug described in the commit message > > when LD_DEAD_CODE_DATA_ELIMINATION is enabled? LTO_CLANG always uses > > LLD, so it won't have this issue. > > LD_DEAD_CODE_DATA_ELIMINATION is marked > “EXPERIMENTAL“ in the config prompt, and > arches have to opt-in > HAS_LD_DEAD_CODE_DATA_ELIMINATION to give > an access to it (only a few does). This > should be relatively safe. > > > Sami > > Thanks, > Al
diff --git a/scripts/module.lds.S b/scripts/module.lds.S index 2c52535f9b56..d6bbdfc55e08 100644 --- a/scripts/module.lds.S +++ b/scripts/module.lds.S @@ -20,11 +20,14 @@ SECTIONS { __patchable_function_entries : { *(__patchable_function_entries) } -#ifdef CONFIG_LTO_CLANG +#if defined(CONFIG_LD_DEAD_CODE_DATA_ELIMINATION) || defined(CONFIG_LTO_CLANG) /* * With CONFIG_LTO_CLANG, LLD always enables -fdata-sections and - * -ffunction-sections, which increases the size of the final module. - * Merge the split sections in the final binary. + * -ffunction-sections. With CONFIG_LD_DEAD_CODE_DATA_ELIMINATION, + * -fdata-sections and -ffunction-sections are being enabled by + * the top-level Makefile. + * This increases the size of the final module. Merge the split + * sections in the final binary. */ .bss : { *(.bss .bss.[0-9a-zA-Z_]*)
When building with CONFIG_LD_DEAD_CODE_DATA_ELIMINATION, -fdata-sections and -ffunction-sections are being enabled by the top-level Makefile, and module section merging is also needed. Expand the ifdef (and the comment block) to cover that case too. Fixes: 6a3193cdd5e5 ("kbuild: lto: Merge module sections if and only if CONFIG_LTO_CLANG is enabled") Signed-off-by: Alexander Lobakin <alobakin@pm.me> --- scripts/module.lds.S | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) -- 2.31.1