[PATCH v2] kbuild: Fix changing ELF file type for output of gen

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* [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

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