* [PATCH v2] kbuild: Fix changing ELF file type for output of gen_btf for big endian
@ 2024-02-13 2:05 Nathan Chancellor
2024-02-13 2:15 ` Masahiro Yamada
` (3 more replies)
0 siblings, 4 replies; 7+ messages in thread
From: Nathan Chancellor @ 2024-02-13 2:05 UTC (permalink / raw
To: masahiroy
Cc: nicolas, ndesaulniers, morbo, justinstitt, keescook, maskray,
linux-kbuild, bpf, llvm, patches, stable, Nathan Chancellor
Commit 90ceddcb4950 ("bpf: Support llvm-objcopy for vmlinux BTF")
changed the ELF type of .btf.vmlinux.bin.o to ET_REL via dd, which works
fine for little endian platforms:
00000000 7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00 |.ELF............|
-00000010 03 00 b7 00 01 00 00 00 00 00 00 80 00 80 ff ff |................|
+00000010 01 00 b7 00 01 00 00 00 00 00 00 80 00 80 ff ff |................|
However, for big endian platforms, it changes the wrong byte, resulting
in an invalid ELF file type, which ld.lld rejects:
00000000 7f 45 4c 46 02 02 01 00 00 00 00 00 00 00 00 00 |.ELF............|
-00000010 00 03 00 16 00 00 00 01 00 00 00 00 00 10 00 00 |................|
+00000010 01 03 00 16 00 00 00 01 00 00 00 00 00 10 00 00 |................|
Type: <unknown>: 103
ld.lld: error: .btf.vmlinux.bin.o: unknown file type
Fix this by updating the entire 16-bit e_type field rather than just a
single byte, so that everything works correctly for all platforms and
linkers.
00000000 7f 45 4c 46 02 02 01 00 00 00 00 00 00 00 00 00 |.ELF............|
-00000010 00 03 00 16 00 00 00 01 00 00 00 00 00 10 00 00 |................|
+00000010 00 01 00 16 00 00 00 01 00 00 00 00 00 10 00 00 |................|
Type: REL (Relocatable file)
While in the area, update the comment to mention that binutils 2.35+
matches LLD's behavior of rejecting an ET_EXEC input, which occurred
after the comment was added.
Cc: stable@vger.kernel.org
Fixes: 90ceddcb4950 ("bpf: Support llvm-objcopy for vmlinux BTF")
Link: https://github.com/llvm/llvm-project/pull/75643
Suggested-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
---
Changes in v2:
- Rather than change the seek value for dd, update the entire e_type
field (Masahiro). Due to this change, I did not carry forward the
tags of v1.
- Slightly update commit message to remove mention of ET_EXEC, which
does not match the dump (Masahiro).
- Update comment to mention binutils 2.35+ has the same behavior as LLD
(Fangrui).
- Link to v1: https://lore.kernel.org/r/20240208-fix-elf-type-btf-vmlinux-bin-o-big-endian-v1-1-cb3112491edc@kernel.org
---
scripts/link-vmlinux.sh | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)
diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
index a432b171be82..7862a8101747 100755
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -135,8 +135,13 @@ gen_btf()
${OBJCOPY} --only-section=.BTF --set-section-flags .BTF=alloc,readonly \
--strip-all ${1} ${2} 2>/dev/null
# Change e_type to ET_REL so that it can be used to link final vmlinux.
- # Unlike GNU ld, lld does not allow an ET_EXEC input.
- printf '\1' | dd of=${2} conv=notrunc bs=1 seek=16 status=none
+ # GNU ld 2.35+ and lld do not allow an ET_EXEC input.
+ if is_enabled CONFIG_CPU_BIG_ENDIAN; then
+ et_rel='\0\1'
+ else
+ et_rel='\1\0'
+ fi
+ printf "${et_rel}" | dd of=${2} conv=notrunc bs=1 seek=16 status=none
}
# Create ${2} .S file with all symbols from the ${1} object file
---
base-commit: 54be6c6c5ae8e0d93a6c4641cb7528eb0b6ba478
change-id: 20240208-fix-elf-type-btf-vmlinux-bin-o-big-endian-dbc55a1e1296
Best regards,
--
Nathan Chancellor <nathan@kernel.org>
^ permalink raw reply related [flat|nested] 7+ messages in thread
* Re: [PATCH v2] kbuild: Fix changing ELF file type for output of gen_btf for big endian
2024-02-13 2:05 [PATCH v2] kbuild: Fix changing ELF file type for output of gen_btf for big endian Nathan Chancellor
@ 2024-02-13 2:15 ` Masahiro Yamada
2024-02-13 2:47 ` Fangrui Song
2024-02-13 20:52 ` Nicolas Schier
2024-02-13 22:19 ` Kees Cook
` (2 subsequent siblings)
3 siblings, 2 replies; 7+ messages in thread
From: Masahiro Yamada @ 2024-02-13 2:15 UTC (permalink / raw
To: Nathan Chancellor
Cc: nicolas, ndesaulniers, morbo, justinstitt, keescook, maskray,
linux-kbuild, bpf, llvm, patches, stable
On Tue, Feb 13, 2024 at 11:06 AM Nathan Chancellor <nathan@kernel.org> wrote:
>
> Commit 90ceddcb4950 ("bpf: Support llvm-objcopy for vmlinux BTF")
> changed the ELF type of .btf.vmlinux.bin.o to ET_REL via dd, which works
> fine for little endian platforms:
>
> 00000000 7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00 |.ELF............|
> -00000010 03 00 b7 00 01 00 00 00 00 00 00 80 00 80 ff ff |................|
> +00000010 01 00 b7 00 01 00 00 00 00 00 00 80 00 80 ff ff |................|
>
> However, for big endian platforms, it changes the wrong byte, resulting
> in an invalid ELF file type, which ld.lld rejects:
>
> 00000000 7f 45 4c 46 02 02 01 00 00 00 00 00 00 00 00 00 |.ELF............|
> -00000010 00 03 00 16 00 00 00 01 00 00 00 00 00 10 00 00 |................|
> +00000010 01 03 00 16 00 00 00 01 00 00 00 00 00 10 00 00 |................|
>
> Type: <unknown>: 103
>
> ld.lld: error: .btf.vmlinux.bin.o: unknown file type
>
> Fix this by updating the entire 16-bit e_type field rather than just a
> single byte, so that everything works correctly for all platforms and
> linkers.
>
> 00000000 7f 45 4c 46 02 02 01 00 00 00 00 00 00 00 00 00 |.ELF............|
> -00000010 00 03 00 16 00 00 00 01 00 00 00 00 00 10 00 00 |................|
> +00000010 00 01 00 16 00 00 00 01 00 00 00 00 00 10 00 00 |................|
>
> Type: REL (Relocatable file)
>
> While in the area, update the comment to mention that binutils 2.35+
> matches LLD's behavior of rejecting an ET_EXEC input, which occurred
> after the comment was added.
>
> Cc: stable@vger.kernel.org
> Fixes: 90ceddcb4950 ("bpf: Support llvm-objcopy for vmlinux BTF")
> Link: https://github.com/llvm/llvm-project/pull/75643
> Suggested-by: Masahiro Yamada <masahiroy@kernel.org>
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Thanks.
I will wait for a few days until
the reviewers come back to give Reviewed-by again.
> ---
> Changes in v2:
> - Rather than change the seek value for dd, update the entire e_type
> field (Masahiro). Due to this change, I did not carry forward the
> tags of v1.
> - Slightly update commit message to remove mention of ET_EXEC, which
> does not match the dump (Masahiro).
> - Update comment to mention binutils 2.35+ has the same behavior as LLD
> (Fangrui).
> - Link to v1: https://lore.kernel.org/r/20240208-fix-elf-type-btf-vmlinux-bin-o-big-endian-v1-1-cb3112491edc@kernel.org
> ---
> scripts/link-vmlinux.sh | 9 +++++++--
> 1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
> index a432b171be82..7862a8101747 100755
> --- a/scripts/link-vmlinux.sh
> +++ b/scripts/link-vmlinux.sh
> @@ -135,8 +135,13 @@ gen_btf()
> ${OBJCOPY} --only-section=.BTF --set-section-flags .BTF=alloc,readonly \
> --strip-all ${1} ${2} 2>/dev/null
> # Change e_type to ET_REL so that it can be used to link final vmlinux.
> - # Unlike GNU ld, lld does not allow an ET_EXEC input.
> - printf '\1' | dd of=${2} conv=notrunc bs=1 seek=16 status=none
> + # GNU ld 2.35+ and lld do not allow an ET_EXEC input.
> + if is_enabled CONFIG_CPU_BIG_ENDIAN; then
> + et_rel='\0\1'
> + else
> + et_rel='\1\0'
> + fi
> + printf "${et_rel}" | dd of=${2} conv=notrunc bs=1 seek=16 status=none
> }
>
> # Create ${2} .S file with all symbols from the ${1} object file
>
> ---
> base-commit: 54be6c6c5ae8e0d93a6c4641cb7528eb0b6ba478
> change-id: 20240208-fix-elf-type-btf-vmlinux-bin-o-big-endian-dbc55a1e1296
>
> Best regards,
> --
> Nathan Chancellor <nathan@kernel.org>
>
>
--
Best Regards
Masahiro Yamada
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH v2] kbuild: Fix changing ELF file type for output of gen_btf for big endian
2024-02-13 2:15 ` Masahiro Yamada
@ 2024-02-13 2:47 ` Fangrui Song
2024-02-13 20:52 ` Nicolas Schier
1 sibling, 0 replies; 7+ messages in thread
From: Fangrui Song @ 2024-02-13 2:47 UTC (permalink / raw
To: Nathan Chancellor
Cc: Masahiro Yamada, nicolas, ndesaulniers, morbo, justinstitt,
keescook, linux-kbuild, bpf, llvm, patches, stable
On Mon, Feb 12, 2024 at 6:16 PM Masahiro Yamada <masahiroy@kernel.org> wrote:
>
> On Tue, Feb 13, 2024 at 11:06 AM Nathan Chancellor <nathan@kernel.org> wrote:
> >
> > Commit 90ceddcb4950 ("bpf: Support llvm-objcopy for vmlinux BTF")
> > changed the ELF type of .btf.vmlinux.bin.o to ET_REL via dd, which works
> > fine for little endian platforms:
> >
> > 00000000 7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00 |.ELF............|
> > -00000010 03 00 b7 00 01 00 00 00 00 00 00 80 00 80 ff ff |................|
> > +00000010 01 00 b7 00 01 00 00 00 00 00 00 80 00 80 ff ff |................|
> >
> > However, for big endian platforms, it changes the wrong byte, resulting
> > in an invalid ELF file type, which ld.lld rejects:
> >
> > 00000000 7f 45 4c 46 02 02 01 00 00 00 00 00 00 00 00 00 |.ELF............|
> > -00000010 00 03 00 16 00 00 00 01 00 00 00 00 00 10 00 00 |................|
> > +00000010 01 03 00 16 00 00 00 01 00 00 00 00 00 10 00 00 |................|
> >
> > Type: <unknown>: 103
> >
> > ld.lld: error: .btf.vmlinux.bin.o: unknown file type
> >
> > Fix this by updating the entire 16-bit e_type field rather than just a
> > single byte, so that everything works correctly for all platforms and
> > linkers.
> >
> > 00000000 7f 45 4c 46 02 02 01 00 00 00 00 00 00 00 00 00 |.ELF............|
> > -00000010 00 03 00 16 00 00 00 01 00 00 00 00 00 10 00 00 |................|
> > +00000010 00 01 00 16 00 00 00 01 00 00 00 00 00 10 00 00 |................|
> >
> > Type: REL (Relocatable file)
> >
> > While in the area, update the comment to mention that binutils 2.35+
> > matches LLD's behavior of rejecting an ET_EXEC input, which occurred
> > after the comment was added.
> >
> > Cc: stable@vger.kernel.org
> > Fixes: 90ceddcb4950 ("bpf: Support llvm-objcopy for vmlinux BTF")
> > Link: https://github.com/llvm/llvm-project/pull/75643
> > Suggested-by: Masahiro Yamada <masahiroy@kernel.org>
> > Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Thanks for updating the comment.
Reviewed-by: Fangrui Song <maskray@google.com>
>
> Thanks.
>
> I will wait for a few days until
> the reviewers come back to give Reviewed-by again.
>
>
>
>
>
> > ---
> > Changes in v2:
> > - Rather than change the seek value for dd, update the entire e_type
> > field (Masahiro). Due to this change, I did not carry forward the
> > tags of v1.
> > - Slightly update commit message to remove mention of ET_EXEC, which
> > does not match the dump (Masahiro).
> > - Update comment to mention binutils 2.35+ has the same behavior as LLD
> > (Fangrui).
> > - Link to v1: https://lore.kernel.org/r/20240208-fix-elf-type-btf-vmlinux-bin-o-big-endian-v1-1-cb3112491edc@kernel.org
> > ---
> > scripts/link-vmlinux.sh | 9 +++++++--
> > 1 file changed, 7 insertions(+), 2 deletions(-)
> >
> > diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
> > index a432b171be82..7862a8101747 100755
> > --- a/scripts/link-vmlinux.sh
> > +++ b/scripts/link-vmlinux.sh
> > @@ -135,8 +135,13 @@ gen_btf()
> > ${OBJCOPY} --only-section=.BTF --set-section-flags .BTF=alloc,readonly \
> > --strip-all ${1} ${2} 2>/dev/null
> > # Change e_type to ET_REL so that it can be used to link final vmlinux.
> > - # Unlike GNU ld, lld does not allow an ET_EXEC input.
> > - printf '\1' | dd of=${2} conv=notrunc bs=1 seek=16 status=none
> > + # GNU ld 2.35+ and lld do not allow an ET_EXEC input.
> > + if is_enabled CONFIG_CPU_BIG_ENDIAN; then
> > + et_rel='\0\1'
> > + else
> > + et_rel='\1\0'
> > + fi
> > + printf "${et_rel}" | dd of=${2} conv=notrunc bs=1 seek=16 status=none
> > }
> >
> > # Create ${2} .S file with all symbols from the ${1} object file
> >
> > ---
> > base-commit: 54be6c6c5ae8e0d93a6c4641cb7528eb0b6ba478
> > change-id: 20240208-fix-elf-type-btf-vmlinux-bin-o-big-endian-dbc55a1e1296
> >
> > Best regards,
> > --
> > Nathan Chancellor <nathan@kernel.org>
> >
> >
>
>
> --
> Best Regards
> Masahiro Yamada
>
--
宋方睿
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH v2] kbuild: Fix changing ELF file type for output of gen_btf for big endian
2024-02-13 2:15 ` Masahiro Yamada
2024-02-13 2:47 ` Fangrui Song
@ 2024-02-13 20:52 ` Nicolas Schier
1 sibling, 0 replies; 7+ messages in thread
From: Nicolas Schier @ 2024-02-13 20:52 UTC (permalink / raw
To: Masahiro Yamada
Cc: Nathan Chancellor, ndesaulniers, morbo, justinstitt, keescook,
maskray, linux-kbuild, bpf, llvm, patches, stable
[-- Attachment #1: Type: text/plain, Size: 4222 bytes --]
On Tue 13 Feb 2024 11:15:40 GMT, Masahiro Yamada wrote:
> On Tue, Feb 13, 2024 at 11:06 AM Nathan Chancellor
> <nathan@kernel.org> wrote:
> >
> > Commit 90ceddcb4950 ("bpf: Support llvm-objcopy for vmlinux BTF")
> > changed the ELF type of .btf.vmlinux.bin.o to ET_REL via dd, which works
> > fine for little endian platforms:
> >
> > 00000000 7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00 |.ELF............|
> > -00000010 03 00 b7 00 01 00 00 00 00 00 00 80 00 80 ff ff |................|
> > +00000010 01 00 b7 00 01 00 00 00 00 00 00 80 00 80 ff ff |................|
> >
> > However, for big endian platforms, it changes the wrong byte, resulting
> > in an invalid ELF file type, which ld.lld rejects:
> >
> > 00000000 7f 45 4c 46 02 02 01 00 00 00 00 00 00 00 00 00 |.ELF............|
> > -00000010 00 03 00 16 00 00 00 01 00 00 00 00 00 10 00 00 |................|
> > +00000010 01 03 00 16 00 00 00 01 00 00 00 00 00 10 00 00 |................|
> >
> > Type: <unknown>: 103
> >
> > ld.lld: error: .btf.vmlinux.bin.o: unknown file type
> >
> > Fix this by updating the entire 16-bit e_type field rather than just a
> > single byte, so that everything works correctly for all platforms and
> > linkers.
> >
> > 00000000 7f 45 4c 46 02 02 01 00 00 00 00 00 00 00 00 00 |.ELF............|
> > -00000010 00 03 00 16 00 00 00 01 00 00 00 00 00 10 00 00 |................|
> > +00000010 00 01 00 16 00 00 00 01 00 00 00 00 00 10 00 00 |................|
> >
> > Type: REL (Relocatable file)
> >
> > While in the area, update the comment to mention that binutils 2.35+
> > matches LLD's behavior of rejecting an ET_EXEC input, which occurred
> > after the comment was added.
> >
> > Cc: stable@vger.kernel.org
> > Fixes: 90ceddcb4950 ("bpf: Support llvm-objcopy for vmlinux BTF")
> > Link: https://github.com/llvm/llvm-project/pull/75643
> > Suggested-by: Masahiro Yamada <masahiroy@kernel.org>
> > Signed-off-by: Nathan Chancellor <nathan@kernel.org>
>
>
> Thanks.
>
> I will wait for a few days until
> the reviewers come back to give Reviewed-by again.
thanks, v2 looks even better.
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>
> > ---
> > Changes in v2:
> > - Rather than change the seek value for dd, update the entire e_type
> > field (Masahiro). Due to this change, I did not carry forward the
> > tags of v1.
> > - Slightly update commit message to remove mention of ET_EXEC, which
> > does not match the dump (Masahiro).
> > - Update comment to mention binutils 2.35+ has the same behavior as LLD
> > (Fangrui).
> > - Link to v1: https://lore.kernel.org/r/20240208-fix-elf-type-btf-vmlinux-bin-o-big-endian-v1-1-cb3112491edc@kernel.org
> > ---
> > scripts/link-vmlinux.sh | 9 +++++++--
> > 1 file changed, 7 insertions(+), 2 deletions(-)
> >
> > diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
> > index a432b171be82..7862a8101747 100755
> > --- a/scripts/link-vmlinux.sh
> > +++ b/scripts/link-vmlinux.sh
> > @@ -135,8 +135,13 @@ gen_btf()
> > ${OBJCOPY} --only-section=.BTF --set-section-flags .BTF=alloc,readonly \
> > --strip-all ${1} ${2} 2>/dev/null
> > # Change e_type to ET_REL so that it can be used to link final vmlinux.
> > - # Unlike GNU ld, lld does not allow an ET_EXEC input.
> > - printf '\1' | dd of=${2} conv=notrunc bs=1 seek=16 status=none
> > + # GNU ld 2.35+ and lld do not allow an ET_EXEC input.
> > + if is_enabled CONFIG_CPU_BIG_ENDIAN; then
> > + et_rel='\0\1'
> > + else
> > + et_rel='\1\0'
> > + fi
> > + printf "${et_rel}" | dd of=${2} conv=notrunc bs=1 seek=16 status=none
> > }
> >
> > # Create ${2} .S file with all symbols from the ${1} object file
> >
> > ---
> > base-commit: 54be6c6c5ae8e0d93a6c4641cb7528eb0b6ba478
> > change-id: 20240208-fix-elf-type-btf-vmlinux-bin-o-big-endian-dbc55a1e1296
> >
> > Best regards,
> > --
> > Nathan Chancellor <nathan@kernel.org>
> >
> >
>
>
> --
> Best Regards
> Masahiro Yamada
[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH v2] kbuild: Fix changing ELF file type for output of gen_btf for big endian
2024-02-13 2:05 [PATCH v2] kbuild: Fix changing ELF file type for output of gen_btf for big endian Nathan Chancellor
2024-02-13 2:15 ` Masahiro Yamada
@ 2024-02-13 22:19 ` Kees Cook
2024-02-13 23:56 ` Justin Stitt
2024-02-14 21:37 ` Masahiro Yamada
3 siblings, 0 replies; 7+ messages in thread
From: Kees Cook @ 2024-02-13 22:19 UTC (permalink / raw
To: Nathan Chancellor
Cc: masahiroy, nicolas, ndesaulniers, morbo, justinstitt, maskray,
linux-kbuild, bpf, llvm, patches, stable
On Mon, Feb 12, 2024 at 07:05:10PM -0700, Nathan Chancellor wrote:
> Commit 90ceddcb4950 ("bpf: Support llvm-objcopy for vmlinux BTF")
> changed the ELF type of .btf.vmlinux.bin.o to ET_REL via dd, which works
> fine for little endian platforms:
>
> 00000000 7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00 |.ELF............|
> -00000010 03 00 b7 00 01 00 00 00 00 00 00 80 00 80 ff ff |................|
> +00000010 01 00 b7 00 01 00 00 00 00 00 00 80 00 80 ff ff |................|
>
> However, for big endian platforms, it changes the wrong byte, resulting
> in an invalid ELF file type, which ld.lld rejects:
>
> 00000000 7f 45 4c 46 02 02 01 00 00 00 00 00 00 00 00 00 |.ELF............|
> -00000010 00 03 00 16 00 00 00 01 00 00 00 00 00 10 00 00 |................|
> +00000010 01 03 00 16 00 00 00 01 00 00 00 00 00 10 00 00 |................|
>
> Type: <unknown>: 103
>
> ld.lld: error: .btf.vmlinux.bin.o: unknown file type
>
> Fix this by updating the entire 16-bit e_type field rather than just a
> single byte, so that everything works correctly for all platforms and
> linkers.
>
> 00000000 7f 45 4c 46 02 02 01 00 00 00 00 00 00 00 00 00 |.ELF............|
> -00000010 00 03 00 16 00 00 00 01 00 00 00 00 00 10 00 00 |................|
> +00000010 00 01 00 16 00 00 00 01 00 00 00 00 00 10 00 00 |................|
>
> Type: REL (Relocatable file)
>
> While in the area, update the comment to mention that binutils 2.35+
> matches LLD's behavior of rejecting an ET_EXEC input, which occurred
> after the comment was added.
>
> Cc: stable@vger.kernel.org
> Fixes: 90ceddcb4950 ("bpf: Support llvm-objcopy for vmlinux BTF")
> Link: https://github.com/llvm/llvm-project/pull/75643
> Suggested-by: Masahiro Yamada <masahiroy@kernel.org>
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Writing the u16 looks fine to me.
Reviewed-by: Kees Cook <keescook@chromium.org>
--
Kees Cook
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH v2] kbuild: Fix changing ELF file type for output of gen_btf for big endian
2024-02-13 2:05 [PATCH v2] kbuild: Fix changing ELF file type for output of gen_btf for big endian Nathan Chancellor
2024-02-13 2:15 ` Masahiro Yamada
2024-02-13 22:19 ` Kees Cook
@ 2024-02-13 23:56 ` Justin Stitt
2024-02-14 21:37 ` Masahiro Yamada
3 siblings, 0 replies; 7+ messages in thread
From: Justin Stitt @ 2024-02-13 23:56 UTC (permalink / raw
To: Nathan Chancellor
Cc: masahiroy, nicolas, ndesaulniers, morbo, keescook, maskray,
linux-kbuild, bpf, llvm, patches, stable
Hi,
On Mon, Feb 12, 2024 at 07:05:10PM -0700, Nathan Chancellor wrote:
> Commit 90ceddcb4950 ("bpf: Support llvm-objcopy for vmlinux BTF")
> changed the ELF type of .btf.vmlinux.bin.o to ET_REL via dd, which works
> fine for little endian platforms:
>
> 00000000 7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00 |.ELF............|
> -00000010 03 00 b7 00 01 00 00 00 00 00 00 80 00 80 ff ff |................|
> +00000010 01 00 b7 00 01 00 00 00 00 00 00 80 00 80 ff ff |................|
>
> However, for big endian platforms, it changes the wrong byte, resulting
> in an invalid ELF file type, which ld.lld rejects:
>
> 00000000 7f 45 4c 46 02 02 01 00 00 00 00 00 00 00 00 00 |.ELF............|
> -00000010 00 03 00 16 00 00 00 01 00 00 00 00 00 10 00 00 |................|
> +00000010 01 03 00 16 00 00 00 01 00 00 00 00 00 10 00 00 |................|
>
> Type: <unknown>: 103
>
> ld.lld: error: .btf.vmlinux.bin.o: unknown file type
>
> Fix this by updating the entire 16-bit e_type field rather than just a
> single byte, so that everything works correctly for all platforms and
> linkers.
>
> 00000000 7f 45 4c 46 02 02 01 00 00 00 00 00 00 00 00 00 |.ELF............|
> -00000010 00 03 00 16 00 00 00 01 00 00 00 00 00 10 00 00 |................|
> +00000010 00 01 00 16 00 00 00 01 00 00 00 00 00 10 00 00 |................|
>
> Type: REL (Relocatable file)
>
> While in the area, update the comment to mention that binutils 2.35+
> matches LLD's behavior of rejecting an ET_EXEC input, which occurred
> after the comment was added.
>
> Cc: stable@vger.kernel.org
> Fixes: 90ceddcb4950 ("bpf: Support llvm-objcopy for vmlinux BTF")
> Link: https://github.com/llvm/llvm-project/pull/75643
> Suggested-by: Masahiro Yamada <masahiroy@kernel.org>
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>
I prefer this version to v1 as well. This seems better than setting the
seek value.
Reviewed-by: Justin Stitt <justinstitt@google.com>
> ---
> Changes in v2:
> - Rather than change the seek value for dd, update the entire e_type
> field (Masahiro). Due to this change, I did not carry forward the
> tags of v1.
> - Slightly update commit message to remove mention of ET_EXEC, which
> does not match the dump (Masahiro).
> - Update comment to mention binutils 2.35+ has the same behavior as LLD
> (Fangrui).
> - Link to v1: https://lore.kernel.org/r/20240208-fix-elf-type-btf-vmlinux-bin-o-big-endian-v1-1-cb3112491edc@kernel.org
> ---
> scripts/link-vmlinux.sh | 9 +++++++--
> 1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
> index a432b171be82..7862a8101747 100755
> --- a/scripts/link-vmlinux.sh
> +++ b/scripts/link-vmlinux.sh
> @@ -135,8 +135,13 @@ gen_btf()
> ${OBJCOPY} --only-section=.BTF --set-section-flags .BTF=alloc,readonly \
> --strip-all ${1} ${2} 2>/dev/null
> # Change e_type to ET_REL so that it can be used to link final vmlinux.
> - # Unlike GNU ld, lld does not allow an ET_EXEC input.
> - printf '\1' | dd of=${2} conv=notrunc bs=1 seek=16 status=none
> + # GNU ld 2.35+ and lld do not allow an ET_EXEC input.
> + if is_enabled CONFIG_CPU_BIG_ENDIAN; then
> + et_rel='\0\1'
> + else
> + et_rel='\1\0'
> + fi
> + printf "${et_rel}" | dd of=${2} conv=notrunc bs=1 seek=16 status=none
> }
>
> # Create ${2} .S file with all symbols from the ${1} object file
>
> ---
> base-commit: 54be6c6c5ae8e0d93a6c4641cb7528eb0b6ba478
> change-id: 20240208-fix-elf-type-btf-vmlinux-bin-o-big-endian-dbc55a1e1296
>
> Best regards,
> --
> Nathan Chancellor <nathan@kernel.org>
>
Thanks
Justin
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH v2] kbuild: Fix changing ELF file type for output of gen_btf for big endian
2024-02-13 2:05 [PATCH v2] kbuild: Fix changing ELF file type for output of gen_btf for big endian Nathan Chancellor
` (2 preceding siblings ...)
2024-02-13 23:56 ` Justin Stitt
@ 2024-02-14 21:37 ` Masahiro Yamada
3 siblings, 0 replies; 7+ messages in thread
From: Masahiro Yamada @ 2024-02-14 21:37 UTC (permalink / raw
To: Nathan Chancellor
Cc: nicolas, ndesaulniers, morbo, justinstitt, keescook, maskray,
linux-kbuild, bpf, llvm, patches, stable
On Tue, Feb 13, 2024 at 11:06 AM Nathan Chancellor <nathan@kernel.org> wrote:
>
> Commit 90ceddcb4950 ("bpf: Support llvm-objcopy for vmlinux BTF")
> changed the ELF type of .btf.vmlinux.bin.o to ET_REL via dd, which works
> fine for little endian platforms:
>
> 00000000 7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00 |.ELF............|
> -00000010 03 00 b7 00 01 00 00 00 00 00 00 80 00 80 ff ff |................|
> +00000010 01 00 b7 00 01 00 00 00 00 00 00 80 00 80 ff ff |................|
>
> However, for big endian platforms, it changes the wrong byte, resulting
> in an invalid ELF file type, which ld.lld rejects:
>
> 00000000 7f 45 4c 46 02 02 01 00 00 00 00 00 00 00 00 00 |.ELF............|
> -00000010 00 03 00 16 00 00 00 01 00 00 00 00 00 10 00 00 |................|
> +00000010 01 03 00 16 00 00 00 01 00 00 00 00 00 10 00 00 |................|
>
> Type: <unknown>: 103
>
> ld.lld: error: .btf.vmlinux.bin.o: unknown file type
>
> Fix this by updating the entire 16-bit e_type field rather than just a
> single byte, so that everything works correctly for all platforms and
> linkers.
>
> 00000000 7f 45 4c 46 02 02 01 00 00 00 00 00 00 00 00 00 |.ELF............|
> -00000010 00 03 00 16 00 00 00 01 00 00 00 00 00 10 00 00 |................|
> +00000010 00 01 00 16 00 00 00 01 00 00 00 00 00 10 00 00 |................|
>
> Type: REL (Relocatable file)
>
> While in the area, update the comment to mention that binutils 2.35+
> matches LLD's behavior of rejecting an ET_EXEC input, which occurred
> after the comment was added.
>
> Cc: stable@vger.kernel.org
> Fixes: 90ceddcb4950 ("bpf: Support llvm-objcopy for vmlinux BTF")
> Link: https://github.com/llvm/llvm-project/pull/75643
> Suggested-by: Masahiro Yamada <masahiroy@kernel.org>
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>
> ---
Applied to linux-kbuild/fixes.
Thanks.
--
Best Regards
Masahiro Yamada
^ permalink raw reply [flat|nested] 7+ messages in thread
end of thread, other threads:[~2024-02-14 21:38 UTC | newest]
Thread overview: 7+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2024-02-13 2:05 [PATCH v2] kbuild: Fix changing ELF file type for output of gen_btf for big endian Nathan Chancellor
2024-02-13 2:15 ` Masahiro Yamada
2024-02-13 2:47 ` Fangrui Song
2024-02-13 20:52 ` Nicolas Schier
2024-02-13 22:19 ` Kees Cook
2024-02-13 23:56 ` Justin Stitt
2024-02-14 21:37 ` Masahiro Yamada
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.