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lld/ELF: Report errors for certain unknown section types #84812

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MaskRay opened this issue Mar 11, 2024 · 1 comment · Fixed by #85173
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lld/ELF: Report errors for certain unknown section types #84812

MaskRay opened this issue Mar 11, 2024 · 1 comment · Fixed by #85173
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MaskRay commented Mar 11, 2024 •
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From https://maskray.me/blog/2024-03-09-a-compact-relocation-format-for-elf#linker-notes

GNU ld allows certain unknown section types:

  • [SHT_LOUSER,SHT_HIUSER] and non-SHF_ALLOC
  • [SHT_LOOS,SHT_HIOS] and non-SHF_OS_NONCONFORMING

but reports errors and stops linking for others (unless --no-warn-mismatch is specified).
When linking a relocatable file using SHT_RELLEB, you might encounter errors like the following:

% myclang -mrelleb -fuse-ld=bfd a.c b.c
/usr/bin/ld.bfd: unknown architecture of input file `/tmp/a-1e0778.o' is incompatible with i386:x86-64 output
/usr/bin/ld.bfd: unknown architecture of input file `/tmp/b-9963f0.o' is incompatible with i386:x86-64 output
/usr/bin/ld.bfd: error in /tmp/a-1e0778.o(.eh_frame); no .eh_frame_hdr table will be created
/usr/bin/ld.bfd: error in /tmp/b-9963f0.o(.eh_frame); no .eh_frame_hdr table will be created
clang: error: linker command failed with exit code 1 (use -v to see invocation)
% myclang -mrelleb -fuse-ld=bfd a.c b.c -Wl,--no-warn-mismatch && ./a.out
/usr/bin/ld.bfd: error in /tmp/a-a1a5f4.o(.eh_frame); no .eh_frame_hdr table will be created
/usr/bin/ld.bfd: error in /tmp/b-9dd23c.o(.eh_frame); no .eh_frame_hdr table will be created
[1]    2459175 segmentation fault  ./a.out

I have a prototype for a new relocation format (RELLEB). Linking a.o and b.o with unpatched lld and gold create an output file with unrelocated .text and will crash at run-time.
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llvmbot commented Mar 11, 2024

@llvm/issue-subscribers-lld-elf

Author: Fangrui Song (MaskRay)

From https://maskray.me/blog/2024-03-09-a-compact-relocation-format-for-elf#linker-notes

GNU ld allows certain unknown section types:

  • [SHT_LOUSER,SHT_HIUSER] and non-SHF_ALLOC
  • [SHT_LOOS,SHT_HIOS] and non-SHF_OS_NONCONFORMING

but reports errors and stops linking for others (unless --no-warn-mismatch is specified).
When linking a relocatable file using SHT_RELLEB, you might encounter errors like the following:

% clang -mrelleb -fuse-ld=bfd a.c b.c
/usr/bin/ld.bfd: unknown architecture of input file `/tmp/a-1e0778.o' is incompatible with i386:x86-64 output
/usr/bin/ld.bfd: unknown architecture of input file `/tmp/b-9963f0.o' is incompatible with i386:x86-64 output
/usr/bin/ld.bfd: error in /tmp/a-1e0778.o(.eh_frame); no .eh_frame_hdr table will be created
/usr/bin/ld.bfd: error in /tmp/b-9963f0.o(.eh_frame); no .eh_frame_hdr table will be created
clang: error: linker command failed with exit code 1 (use -v to see invocation)

I have a prototype for a new relocation format (RELLEB). Linking a.o and b.o with unpatched lld and gold create an output file with unrelocated .text and will crash at run-time.

@MaskRay MaskRay mentioned this issue Mar 11, 2024
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@MaskRay MaskRay self-assigned this Mar 11, 2024
@MaskRay MaskRay mentioned this issue Mar 14, 2024
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MaskRay added a commit that referenced this issue Mar 15, 2024
@MaskRay
[ELF] Reject certain unknown section types (#85173)
e115c00 
Unknown section sections may require special linking rules, and
rejecting such sections for older linkers may be desired. For example,
if we introduce a new section type to replace a control structure (e.g.
relocations), it would be nice for older linkers to reject the new
section type. GNU ld allows certain unknown section types:

* [SHT_LOUSER,SHT_HIUSER] and non-SHF_ALLOC
* [SHT_LOOS,SHT_HIOS] and non-SHF_OS_NONCONFORMING

but reports errors and stops linking for others (unless
--no-warn-mismatch is specified). Port its behavior. For convenience, we
additionally allow all [SHT_LOPROC,SHT_HIPROC] types so that we don't
have to hard code all known types for each processor.

Close #84812
ilovepi pushed a commit to ilovepi/llvm-project that referenced this issue Mar 15, 2024
@MaskRay @ilovepi
[ELF] Reject certain unknown section types (llvm#85173)
8f2aab2 
Unknown section sections may require special linking rules, and
rejecting such sections for older linkers may be desired. For example,
if we introduce a new section type to replace a control structure (e.g.
relocations), it would be nice for older linkers to reject the new
section type. GNU ld allows certain unknown section types:

* [SHT_LOUSER,SHT_HIUSER] and non-SHF_ALLOC
* [SHT_LOOS,SHT_HIOS] and non-SHF_OS_NONCONFORMING

but reports errors and stops linking for others (unless
--no-warn-mismatch is specified). Port its behavior. For convenience, we
additionally allow all [SHT_LOPROC,SHT_HIPROC] types so that we don't
have to hard code all known types for each processor.

Close llvm#84812
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