specs: document ELF note-merging semantics for dlopen and package metadata#222
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xnox wants to merge 1 commit into
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specs: document ELF note-merging semantics for dlopen and package metadata#222xnox wants to merge 1 commit into
xnox wants to merge 1 commit into
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…adata Linkers concatenate same-named sections from multiple input files, so a linked binary can carry multiple .note.dlopen or .note.package notes even when each producer emitted only one. Parsers must therefore iterate over one or more Note structures rather than assuming a single note. Add a "Guidance on parsing ELF sections" section to both specs describing this, with a readelf example. Make the two specs share the same parsing procedure: this behavior is forced by the ELF spec and by the binutils ld and LLVM lld implementations, and was already the long-standing status quo for dlopen metadata (one note per dependency or one combined note), so the package metadata spec now inherits it. For package metadata, note the SCA/SBOM/vulnerability-matching implication: multiple notes indicate a likely statically linked binary composed from several packages, all of which must be enumerated.
poettering
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Jul 8, 2026
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| ## Guidance on parsing ELF sections | ||
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| When ELF linkers encounter an identical section name across multiple input files, the sections are concatenated in the order they appear, padded and aligned. This merging is standard linker behavior and is generally not under the control of the tool that emits the note. See the [binutils ld](https://sourceware.org/binutils/docs/ld/SECTIONS.html) documentation as well as [LLVM lld](https://releases.llvm.org/22.1.0/tools/lld/docs/ELF/linker_script.html#linker-script-implementation-notes-and-policy), which describe the same behavior. |
Collaborator
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padded/aligned to what?
Author
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it is a bit convoluted - it is 4 bytes; but also the max bytes of all sections being merged if different alignment specified, and could be 8.
will collect precise wording from the ELF spec and ld implementation to be precise & concise.
Will be able to get to this in a weeks time.
poettering
reviewed
Jul 8, 2026
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| ## Guidance on parsing ELF sections | ||
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| When ELF linkers encounter an identical section name across multiple input files, the sections are concatenated in the order they appear, padded and aligned. This merging is standard linker behavior and is generally not under the control of the tool that emits the note. See the [binutils ld](https://sourceware.org/binutils/docs/ld/SECTIONS.html) documentation as well as [LLVM lld](https://releases.llvm.org/22.1.0/tools/lld/docs/ELF/linker_script.html#linker-script-implementation-notes-and-policy), which describe the same behavior. |
Collaborator
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padded/aligned to what?
Collaborator
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lgtm, but be more precise regarding the padding/alignment, as suggested |
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Linkers concatenate same-named sections from multiple input files, so a
linked binary can carry multiple .note.dlopen or .note.package notes even
when each producer emitted only one. Parsers must therefore iterate over
one or more Note structures rather than assuming a single note.
Add a "Guidance on parsing ELF sections" section to both specs describing
this, with a readelf example. Make the two specs share the same parsing
procedure: this behavior is forced by the ELF spec and by the binutils ld
and LLVM lld implementations, and was already the long-standing status quo
for dlopen metadata (one note per dependency or one combined note), so the
package metadata spec now inherits it.
For package metadata, note the SCA/SBOM/vulnerability-matching implication:
multiple notes indicate a likely statically linked binary composed from
several packages, all of which must be enumerated.