[llvm] r323783 - CodeGen: support an extension to pass linker options on ELF

[via llvm-commits]

> -----Original Message-----
> From: llvm-commits [mailto:llvm-commits-bounces at lists.llvm.org] On Behalf
> Of Justin Bogner via llvm-commits
> Sent: Tuesday, January 30, 2018 11:35 PM
> To: Saleem Abdulrasool via llvm-commits
> Subject: Re: [llvm] r323783 - CodeGen: support an extension to pass linker
> options on ELF
> 
> Saleem Abdulrasool via llvm-commits <llvm-commits at lists.llvm.org>
> writes:
> > Author: compnerd
> > Date: Tue Jan 30 08:29:29 2018
> > New Revision: 323783
> >
> > URL: http://llvm.org/viewvc/llvm-project?rev=323783&view=rev
> > Log:
> > CodeGen: support an extension to pass linker options on ELF
> >
> > Introduce an extension to support passing linker options to the linker.
> > These would be ignored by older linkers, but newer linkers which support
> > this feature would be able to process the linker.
> >
> > Emit a special discarded section `.linker-option`.  The content of this
> > section is a pair of strings (key, value).  The key is a type identifier
> for
> > the parameter.  This allows for an argument free parameter that will be
> > processed by the linker with the value being the parameter.  As an
> example,
> > `lib` identifies a library to be linked against, traditionally the `-l`
> > argument for Unix-based linkers with the parameter being the library
> name.
> >
> > Thanks to James Henderson, Cary Coutant, Rafael Espinolda, Sean Silva
> > for the valuable discussion on the design of this feature.
>  ...
> > Added: llvm/trunk/test/Feature/elf-linker-options.ll
> > URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Feature/elf-
> linker-options.ll?rev=323783&view=auto
> >
> ==========================================================================
> ====
> > --- llvm/trunk/test/Feature/elf-linker-options.ll (added)
> > +++ llvm/trunk/test/Feature/elf-linker-options.ll Tue Jan 30 08:29:29
> 2018
> > @@ -0,0 +1,16 @@
> > +; RUN: llc -mtriple x86_64-elf -filetype asm -o - %s | FileCheck %s
> > +
> > +!llvm.linker.options = !{!0, !1}
> > +
> > +!0 = !{!"option 0", !"value 0"}
> > +!1 = !{!"option 1", !"value 1"}
> > +
> > +; CHECK: .section ".linker-options","e", at llvm_linker_options
> > +; CHECK-NEXT: .ascii  "option 0"
> > +; CHECK-NEXT: .byte   0
> > +; CHECK-NEXT: .ascii  "value 0"
> > +; CHECK-NEXT: .byte   0
> > +; CHECK-NEXT: .ascii  "option 1"
> > +; CHECK-NEXT: .byte   0
> > +; CHECK-NEXT: .ascii  "value 1"
> > +; CHECK-NEXT: .byte   0
> >
> > Added: llvm/trunk/test/tools/llvm-readobj/elf-linker-options.ll
> > URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/tools/llvm-
> readobj/elf-linker-options.ll?rev=323783&view=auto
> >
> ==========================================================================
> ====
> > --- llvm/trunk/test/tools/llvm-readobj/elf-linker-options.ll (added)
> > +++ llvm/trunk/test/tools/llvm-readobj/elf-linker-options.ll Tue Jan 30
> 08:29:29 2018
> > @@ -0,0 +1,11 @@
> > +; RUN: llc -mtriple x86_64-elf -filetype obj -o - %s | llvm-readobj -
> elf-linker-options - | FileCheck %s
> > +
> > +!llvm.linker.options = !{!0, !1}
> > +
> > +!0 = !{!"option 0", !"value 0"}
> > +!1 = !{!"option 1", !"value 1"}
> > +
> > +; CHECK: LinkerOptions [
> > +; CHECK:  option 0: value 0
> > +; CHECK:  option 1: value 1
> > +; CHECK: ]
> >
> 
> These two tests both use an x86 triple, so they fail if no x86 backend
> is built. I've marked them "REQUIRES: x86-registered-target" in r323847
> to unbreak bots, but if the triple isn't needed it might make more sense
> to remove it and mark these "REQUIRES: default_triple" instead.

Really it required the default triple to be an ELF target, and I don't
think we have a way to express that in REQUIRES?  If that's the case,
then what Justin did seems like the best solution (although it might be
worth a comment explaining what's actually needed).
--paulr

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