| Message ID | 20191011000609.29728-3-keescook@chromium.org (mailing list archive) |
|---|---|
| State | Mainlined |
| Commit | 6fc4000656a10fb679ab6566dcd516ee672f1706 |
| Headers | show |
| Series | vmlinux.lds.h: Refactor EXCEPTION_TABLE and NOTES | expand |
Kees Cook <keescook@chromium.org> writes: > In preparation for moving NOTES into RO_DATA, remove the PT_NOTE > workaround since the kernel requires at least gcc 4.6 now. > > Signed-off-by: Kees Cook <keescook@chromium.org> > --- > arch/powerpc/kernel/vmlinux.lds.S | 24 ++---------------------- > 1 file changed, 2 insertions(+), 22 deletions(-) Acked-by: Michael Ellerman <mpe@ellerman.id.au> For the archives, Joel tried a similar patch a while back which caused some problems, see: https://lore.kernel.org/linuxppc-dev/20190321003253.22100-1-joel@jms.id.au/ and a v2: https://lore.kernel.org/linuxppc-dev/20190329064453.12761-1-joel@jms.id.au/ This is similar to his v2. The only outstanding comment on his v2 was from Segher: (And I do not know if there are any tools that expect the notes in a phdr, or even specifically the second phdr). But this patch solves that by not changing the note. cheers > diff --git a/arch/powerpc/kernel/vmlinux.lds.S b/arch/powerpc/kernel/vmlinux.lds.S > index 81e672654789..a3c8492b2b19 100644 > --- a/arch/powerpc/kernel/vmlinux.lds.S > +++ b/arch/powerpc/kernel/vmlinux.lds.S > @@ -20,20 +20,6 @@ ENTRY(_stext) > PHDRS { > kernel PT_LOAD FLAGS(7); /* RWX */ > note PT_NOTE FLAGS(0); > - dummy PT_NOTE FLAGS(0); > - > - /* binutils < 2.18 has a bug that makes it misbehave when taking an > - ELF file with all segments at load address 0 as input. This > - happens when running "strip" on vmlinux, because of the AT() magic > - in this linker script. People using GCC >= 4.2 won't run into > - this problem, because the "build-id" support will put some data > - into the "notes" segment (at a non-zero load address). > - > - To work around this, we force some data into both the "dummy" > - segment and the kernel segment, so the dummy segment will get a > - non-zero load address. It's not enough to always create the > - "notes" segment, since if nothing gets assigned to it, its load > - address will be zero. */ > } > > #ifdef CONFIG_PPC64 > @@ -178,14 +164,8 @@ SECTIONS > EXCEPTION_TABLE(0) > > NOTES :kernel :note > - > - /* The dummy segment contents for the bug workaround mentioned above > - near PHDRS. */ > - .dummy : AT(ADDR(.dummy) - LOAD_OFFSET) { > - LONG(0) > - LONG(0) > - LONG(0) > - } :kernel :dummy > + /* Restore program header away from PT_NOTE. */ > + .dummy : { *(.dummy) } :kernel > > /* > * Init sections discarded at runtime > -- > 2.17.1
On Fri, Oct 11, 2019 at 05:07:04PM +1100, Michael Ellerman wrote: > Kees Cook <keescook@chromium.org> writes: > > In preparation for moving NOTES into RO_DATA, remove the PT_NOTE > > workaround since the kernel requires at least gcc 4.6 now. > > > > Signed-off-by: Kees Cook <keescook@chromium.org> > > --- > > arch/powerpc/kernel/vmlinux.lds.S | 24 ++---------------------- > > 1 file changed, 2 insertions(+), 22 deletions(-) > > Acked-by: Michael Ellerman <mpe@ellerman.id.au> Thanks! > For the archives, Joel tried a similar patch a while back which caused > some problems, see: > > https://lore.kernel.org/linuxppc-dev/20190321003253.22100-1-joel@jms.id.au/ > > and a v2: > > https://lore.kernel.org/linuxppc-dev/20190329064453.12761-1-joel@jms.id.au/ > > This is similar to his v2. The only outstanding comment on his v2 was > from Segher: > (And I do not know if there are any tools that expect the notes in a phdr, > or even specifically the second phdr). > > But this patch solves that by not changing the note. Ah yes. Agreed: I'm retaining the note and dropping the workarounds. FWIW, this builds happily for me in my tests. -Kees
diff --git a/arch/powerpc/kernel/vmlinux.lds.S b/arch/powerpc/kernel/vmlinux.lds.S index 81e672654789..a3c8492b2b19 100644 --- a/arch/powerpc/kernel/vmlinux.lds.S +++ b/arch/powerpc/kernel/vmlinux.lds.S @@ -20,20 +20,6 @@ ENTRY(_stext) PHDRS { kernel PT_LOAD FLAGS(7); /* RWX */ note PT_NOTE FLAGS(0); - dummy PT_NOTE FLAGS(0); - - /* binutils < 2.18 has a bug that makes it misbehave when taking an - ELF file with all segments at load address 0 as input. This - happens when running "strip" on vmlinux, because of the AT() magic - in this linker script. People using GCC >= 4.2 won't run into - this problem, because the "build-id" support will put some data - into the "notes" segment (at a non-zero load address). - - To work around this, we force some data into both the "dummy" - segment and the kernel segment, so the dummy segment will get a - non-zero load address. It's not enough to always create the - "notes" segment, since if nothing gets assigned to it, its load - address will be zero. */ } #ifdef CONFIG_PPC64 @@ -178,14 +164,8 @@ SECTIONS EXCEPTION_TABLE(0) NOTES :kernel :note - - /* The dummy segment contents for the bug workaround mentioned above - near PHDRS. */ - .dummy : AT(ADDR(.dummy) - LOAD_OFFSET) { - LONG(0) - LONG(0) - LONG(0) - } :kernel :dummy + /* Restore program header away from PT_NOTE. */ + .dummy : { *(.dummy) } :kernel /* * Init sections discarded at runtime
In preparation for moving NOTES into RO_DATA, remove the PT_NOTE workaround since the kernel requires at least gcc 4.6 now. Signed-off-by: Kees Cook <keescook@chromium.org> --- arch/powerpc/kernel/vmlinux.lds.S | 24 ++---------------------- 1 file changed, 2 insertions(+), 22 deletions(-)