On Wed, Jun 24, 2020 at 10:26:20AM -0700, Fangrui Song wrote:

On 2020-06-24, Arvind Sankar wrote:

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On Wed, Jun 24, 2020 at 09:16:43AM -0700, Fangrui Song wrote:

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On 2020-06-24, Arvind Sankar wrote:

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On Tue, Jun 23, 2020 at 06:49:33PM -0700, Kees Cook wrote:

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When linking vmlinux with LLD, the synthetic sections .symtab, .strtab,
and .shstrtab are listed as orphaned. Add them to the STABS_DEBUG section
so there will be no warnings when --orphan-handling=warn is used more
widely. (They are added above comment as it is the more common

Nit 1: is "after .comment" better than "above comment"? It's above in the
sense of higher file offset, but it's below in readelf output.

I mean this order:)

   .comment
   .symtab
   .shstrtab
   .strtab

This is the case in the absence of a linker script if at least one object file has .comment (mostly for GCC/clang version information) or the linker is LLD which adds a .comment

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Nit 2: These aren't actually debugging sections, no? Is it better to add
a new macro for it, and is there any plan to stop LLD from warning about
them?

https://reviews.llvm.org/D75149 "[ELF] --orphan-handling=: don't warn/error for unused synthesized sections"
described that .symtab .shstrtab .strtab are different in GNU ld.
Since many other GNU ld synthesized sections (.rela.dyn .plt ...) can be renamed or dropped
via output section descriptions, I don't understand why the 3 sections
can't be customized.

So IIUC, lld will now warn about .rela.dyn etc only if they're non-empty?

HEAD and future 11.0.0 will not warn about unused synthesized sections
like .rela.dyn

For most synthesized sections, empty = unused.

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I created a feature request: https://sourceware.org/bugzilla/show_bug.cgi?id=26168
(If this is supported, it is a consistent behavior to warn for orphan
.symtab/.strtab/.shstrtab

There may be 50% chance that the maintainer decides that "LLD diverges"
I would disagree: there is no fundamental problems with .symtab/.strtab/.shstrtab which make them special in output section descriptions or orphan handling.)

.shstrtab is a little special in that it can't be discarded if the ELF
file contains any sections at all. But yeah, there's no reason they
can't be renamed or placed in a custom location in the file.

https://sourceware.org/pipermail/binutils/2020-March/000179.html
proposes -z nosectionheader. With this option, I believe .shstrtab is
not needed. /DISCARD/ : { *(.shstrtab) }  should achieve a similar effect.

oh wow.

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