[ELF] Allow discarding of .rela.plt

[martell]

Summary

When linking the linux kernel on ppc64 le

ld.lld -EL -m elf64lppc -Bstatic --orphan-handling=warn --build-id -o .tmp_vmlinux1 -T ./arch/powerpc/kernel/vmlinux.lds --whole-archive built-in.a --no-whole-archive --start-group lib/lib.a --end-group
ld.lld: error: discarding .rela.plt section is not allowed

[martell]

update tests

[grimar]

This is probably fine. The test was introduced in D41640.

Before D41640 the constructions like /DISCARD/ : { *(.rela.plt) were completely ignored,
but after that patch, we could discard them or report an error.

I think we report an error just because it seems uncommon for scripts to discard this section
and we never faced that before. I assume your script do that, is it correct?
(I did not find how the macro DISCARDS expands in
https://github.com/spotify/linux/blob/master/arch/powerpc/kernel/vmlinux.lds.S#L262)

[ruiu]

Yeah I believe this is fine too. LGTM.

[martell]

In D54871#1307606, @grimar wrote:

(I did not find how the macro DISCARDS expands in
https://github.com/spotify/linux/blob/master/arch/powerpc/kernel/vmlinux.lds.S#L262)

Sorry only getting around to this comment now. I think this is probably what you are looking for
https://github.com/torvalds/linux/blob/master/arch/powerpc/kernel/vmlinux.lds.S#L387

[grimar]

In D54871#1318300, @martell wrote:

In D54871#1307606, @grimar wrote:

(I did not find how the macro DISCARDS expands in
https://github.com/spotify/linux/blob/master/arch/powerpc/kernel/vmlinux.lds.S#L262)

Sorry only getting around to this comment now. I think this is probably what you are looking for
https://github.com/torvalds/linux/blob/master/arch/powerpc/kernel/vmlinux.lds.S#L387

Thanks!

ELF/LinkerScript.cpp

sortInputSections(MutableArrayRef<InputSection *>(Ret).slice(SizeBefore),
                       Pat);
   }
   return Ret;
 }
 
 void LinkerScript::discard(ArrayRef<InputSection *> V) {
   for (InputSection *S : V) {
     if (S == In.ShStrTab || S == In.Dynamic || S == In.DynSymTab ||
-        S == In.DynStrTab || S == In.RelaPlt || S == In.RelaDyn ||
-        S == In.RelrDyn)
+        S == In.DynStrTab || S == In.RelaDyn || S == In.RelrDyn)
       error("discarding " + S->Name + " section is not allowed");
 
     // You can discard .hash and .gnu.hash sections by linker scripts. Since
     // they are synthesized sections, we need to handle them differently than
     // other regular sections.
     if (S == In.GnuHashTab)
       In.GnuHashTab = nullptr;
     if (S == In.HashTab)

test/ELF/linkerscript/discard-section-err.s

 # RUN:   FileCheck -check-prefix=DYNSYM %s
 # DYNSYM: discarding .dynsym section is not allowed
 
 # RUN: echo "SECTIONS { /DISCARD/ : { *(.dynstr) } }" > %t.script
 # RUN: not ld.lld -pie -o %t --script %t.script %t.o 2>&1 | \
 # RUN:   FileCheck -check-prefix=DYNSTR %s
 # DYNSTR: discarding .dynstr section is not allowed
 
-# RUN: echo "SECTIONS { /DISCARD/ : { *(.rela.plt) } }" > %t.script
-# RUN: not ld.lld -pie -o %t --script %t.script %t.o 2>&1 | \
-# RUN:   FileCheck -check-prefix=RELAPLT %s
-# RELAPLT: discarding .rela.plt section is not allowed
-
 # RUN: echo "SECTIONS { /DISCARD/ : { *(.rela.dyn) } }" > %t.script
 # RUN: not ld.lld -pie -o %t --script %t.script %t.o 2>&1 | \
 # RUN:   FileCheck -check-prefix=RELADYN %s
 # RELADYN: discarding .rela.dyn section is not allowed
 
 .comm foo,4,4