Re: [RFC] SHF_GNU_RETAIN ELF Section Flag

[Jozef Lawrynowicz <jozef.l@mittosystems.com>]

Hi,

Where do we stand on this proposal?

Unless we are trying to be protective of the remaining operating
system-specific section flag bits, I don't really see any downside to
going the route of SHF_GNU_RETAIN. It is very simple, the linker
implementation requires only one additional line of code, and the
definition precisely describes how the section should be treated.

SHF_GNU_RETAIN
  The link editor should not garbage collect the section if it is
  unused.

I don't think the extra detail about whether the link editor sees the
section or not (in the case of libraries) is actually needed.

The definition explicitly states exactly what the linker should do - do
not garbage collect the section. It does not say "the linker should keep
the section if it is unused". Garbage collection implies the linker
"had" the section to begin with.

Perhaps the ambiguity in this area comes from the word "retain" in the
flag name, but again this has a precise definition. You cannot retain
something you don't have. To use the word "encounters" which is used
throughout the ELF spec:

If the linker doesn't encounter a section, it can't retain it. The
linker doesn't encounter any sections from libraries until it loads
an object file needed to resolve a symbol reference, so this behavior is
also precisely defined by the above definition.

If we really need to, we could add emphasize the "garbage collection"
aspect further:

SHF_GNU_RETAIN
  When performing garbage collection of unused sections, the link editor
  should not discard the section, even if it appears unused.

Are there any other objections to adding this to the GNU gABI?

Thanks,
Jozef