On Tue, 8 Aug 2017 12:42:18 +0900 Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx> wrote: > Hi Nicholas, > > 2017-08-08 12:19 GMT+09:00 Nicholas Piggin <npiggin@xxxxxxxxx>: > > On Tue, 8 Aug 2017 10:53:56 +0900 > > Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx> wrote: > > > >> Hi Nicholas, > >> > >> 2017-07-26 21:46 GMT+09:00 Nicholas Piggin <npiggin@xxxxxxxxx>: > >> > The .data and .bss sections were modified in the generic linker script to > >> > pull in sections named .data.<C identifier>, which are generated by gcc with > >> > -ffunction-sections and -fdata-sections options. > >> > > >> > The problem with this pattern is it can also match section names that Linux > >> > defines explicitly, e.g., .data.unlikely. This can cause Linux sections to > >> > get moved into the wrong place. > >> > > >> > The way to avoid this is to use ".." separators for explicit section names > >> > (the dot character is valid in a section name but not a C identifier). > >> > However currently there are sections which don't follow this rule, so for > >> > now just disable the wild card by default. > >> > > >> > Example: http://marc.info/?l=linux-arm-kernel&m=150106824024221&w=2 > >> > > >> > Cc: <stable@xxxxxxxxxxxxxxx> # 4.9 > >> > Fixes: b67067f1176df ("kbuild: allow archs to select link dead code/data elimination") > >> > Signed-off-by: Nicholas Piggin <npiggin@xxxxxxxxx> > >> > --- > >> > include/asm-generic/vmlinux.lds.h | 38 ++++++++++++++++++++++++++------------ > >> > 1 file changed, 26 insertions(+), 12 deletions(-) > >> > > >> > diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h > >> > index da0be9a8d1de..9623d78f8494 100644 > >> > --- a/include/asm-generic/vmlinux.lds.h > >> > +++ b/include/asm-generic/vmlinux.lds.h > >> > @@ -60,6 +60,22 @@ > >> > #define ALIGN_FUNCTION() . = ALIGN(8) > >> > > >> > /* > >> > + * LD_DEAD_CODE_DATA_ELIMINATION option enables -fdata-sections, which > >> > + * generates .data.identifier sections, which need to be pulled in with > >> > + * .data. We don't want to pull in .data..other sections, which Linux > >> > + * has defined. Same for text and bss. > >> > + */ > >> > +#ifdef CONFIG_LD_DEAD_CODE_DATA_ELIMINATION > >> > +#define TEXT_MAIN .text .text.[0-9a-zA-Z_]* > >> > +#define DATA_MAIN .data .data.[0-9a-zA-Z_]* > >> > +#define BSS_MAIN .bss .bss.[0-9a-zA-Z_]* > >> > +#else > >> > +#define TEXT_MAIN .text > >> > +#define DATA_MAIN .data > >> > +#define BSS_MAIN .bss > >> > +#endif > >> > >> > >> From the git-log, I think you are planning to rename > >> .data.unlikely -> .data..unlikey > >> then the problem will be fixed. > >> > >> ("git grep data.unlikely" gave me only 7 instances.) > >> > >> > >> Why is this patch necessary? > >> > >> > >> You are trying to migrate some architectures to DCDE, > >> so this #ifdef does not solve the problem, I think. > > > > Well basically I want to preserve previous behaviour and avoid > > regressions as far as possible. Patches to rename existing > > sections I think would not be so suitable for @stable. And > > there could be other things we've missed. > > > > Yes I would like to ensure all our sections use .. separators > > which (hopefully). Until then I think this is a minimal fix. > > > > > After you rename the sections, will you revert this patch? > > I think the #ifdef CONFIG_LD_DEAD_CODE_DATA_ELIMINATION > should not be permanent. Once we have the code reasonably well used on a number of archs, I think we should remove the ifdefs, yes we definitely should be moving toward sharing common code wherever possible. Thanks, Nick -- To unsubscribe from this list: send the line "unsubscribe linux-kbuild" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
