llvm dev - Jun 2015 - [LLVMdev] [lld] How do I prevent .note sections from being eliminated?

Hi,

I'm working on an AMDGPU target for lld, and I'm trying to link a single
.o file with a .note section, but the .note section is missing from the
resulting a.out file.  How can I control which sections get copied over
to the executable?  Is there a target hook to implement?

Thanks,
Tom

Hi,

If you need to control content of output .note section, take a look at
ARMExidxSection, MipsReginfoSection, MipsOptionsSection classes. If
you need to copy sections from input to output, use SDataSection (from
Hexagon) as a reference point.

On Sat, Jun 13, 2015 at 6:28 AM, Tom Stellard <tom at stellard.net>
wrote:
> I'm working on an AMDGPU target for lld, and I'm trying to link a
single
> .o file with a .note section, but the .note section is missing from the
> resulting a.out file.  How can I control which sections get copied over
> to the executable?  Is there a target hook to implement?
Simon

On Sat, Jun 13, 2015 at 01:08:50PM +0300, Simon Atanasyan
wrote:
> Hi,
> 
> If you need to control content of output .note section, take a look at
> ARMExidxSection, MipsReginfoSection, MipsOptionsSection classes. If
> you need to copy sections from input to output, use SDataSection (from
> Hexagon) as a reference point.
> 
Hi Simon,

Thanks for the reply.  I have a few more follow up questions.

ELFFile::handleSectionWithNoSymbols() returns false for SHT_NOTE.  This
means that ELFFile::createAtoms() never creates an atom for .note sections.
It seems like even if I use something like SDataSection, then I will still
need to modify ELFFIle::handleSectionWithNoSymbols().  What is the best
way to do this?  Should I make the function virtual and override it in
AMDGPUELFFile.cpp?

In ELFDefinedAtom::doContentType(), SHT_NOTE sections are only assigned
the typeR[OW]Note ContentType if they have the SHF_ALLOC flag.  This is
because any section without SHF_ALLOC is assigned the typeNoAlloc
ContentType before the section type is ever considered.  Is this a bug
or are SHT_NOTE sections required to have the SHF_ALLOC flag?

Thanks,
Tom
> On Sat, Jun 13, 2015 at 6:28 AM, Tom Stellard <tom at stellard.net>
wrote:
> > I'm working on an AMDGPU target for lld, and I'm trying to
link a single
> > .o file with a .note section, but the .note section is missing from
the
> > resulting a.out file.  How can I control which sections get copied
over
> > to the executable?  Is there a target hook to implement?
> 
> Simon