Messages in this thread | | | From | Florian Weimer <> | Subject | Re: ELF NT_GNU_PROPERTY_TYPE_0 Questions | Date | Thu, 22 Aug 2019 13:12:53 +0200 |
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* Dave Martin:
> Hi there, > > Can you clarify a couple of points about the SysV ABI Linux > Extensions [1] for me? > > 1) Can there be more than one NT_GNU_PROPERTY_TYPE_0 note in a valid > ELF file? I think the answer should be "no".
Yes, if it has been produced by a link editors which does not about property notes. The ELF file still needs to be treated as valid, but the note should be ignored.
> 2) Is is permissible for an ELF ET_EXEC or ET_DYN file that contains > an NT_GNU_PROPERTY_TYPE_0 property not to have a PT_GNU_PROPERTY phdrs > entry mapping it? Except for historical usage by RedHat (which > apparently can be worked round in userspace) it seems reasonable for > the answer to be "no", at least for Linux.
Using an older link editor on a CET-enabled distribution will produce such binaries, too. The ELF file still needs to be treated as valid, but the property date should be ignored.
> 3) Is it permissible for the PT_GNU_PROPERTY phdr (if present) to > map anything other than precisely one NT_GNU_PROPERTY_TYPE_0 > note? I think the answer should be "no".
Correct. Additional processing logic in the link editor is needed.
> 4) Is an NT_GNU_PROPERTY_TYPE_0 note allowed to contain two or more > properties with the same pr_type? I think the answer should be "no".
H.J. needs to answer that.
> 5) What's the rationale for sorting the properties by pr_type? I can > see this would make it easier for the linker to merge > NT_GNU_PROPERTY_TYPE_0 notes from different files, but I'm wondering > whether the kernel really needs to enforce the ordering when loading > an ELF. The kernel doesn't need to merge property lists together.
Likewise.
> 6) Do you have a view on the best way to define the Elf_Prop type in > headers? bfd elf-bfd.h seems to have elf_property, but this doesn't > follow the style of the public ELF headers.
We should put it into <elf.h> in glibc. We don't want to rely on UAPI headers there because this version of <elf.h> is used in many places.
Thanks, Florian
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