Fix crash when processing relocations in .eh_frame

[arichardson]

Summary

This happens when attempting to link shared libraries using exceptions on
MIPS. It requires -z notext because clang generates R_MIPS_64 relocations
inside .eh_frame.
The crash happened because for EhInputSection the OutSec member is null.

[grimar]

test/ELF/mips64-eh-abs-reloc.s

2

You're missing REQUIRES: mips

4

We do not check what llvm-mc produces in tests for LLD I think.

14

Not sure why do you need to check this. Did executable case crash before this patch ?
Generally I think you just need simplest test that crashed before and do not crash after.

[arichardson]

Simplified the test case

[arichardson]

test/ELF/mips64-eh-abs-reloc.s

4

I only have this line here to make sure that there is a R_MIPS_64 relocation in .eh_frame in case llvm-mc changes. I could also change it to use a YAML testcase but to me the assembly version is easier to understand.

14

Only shared lib and -pie executable case would crash before, so I've deleted all but those.

[atanasyan]

LGTM with the latest fixes.

Just a side note - this patch fix allows linking with the -z notext option. GNU and gold linkers work even without this option. They convert absolute R_MIPS_32/64 relocations against .eh_frame section into relative equivalents.

[arichardson]

I don't have commit access, could you commit for me please?

[arichardson]

Submitted as rL304260

ELF/SyntheticSections.cpp

case Entry::PlainInt:
       P->d_un.d_val = E.Val;
       break;
     }
     ++P;
   }
 }
 
 uint64_t DynamicReloc::getOffset() const {
-  return InputSec->OutSec->Addr + InputSec->getOffset(OffsetInSec);
+  return InputSec->getOutputSection()->Addr + InputSec->getOffset(OffsetInSec);
 }
 
 int64_t DynamicReloc::getAddend() const {
   if (UseSymVA)
     return Sym->getVA(Addend);
   return Addend;
 }
 

test/ELF/mips64-eh-abs-reloc.s

+# Having an R_MIPS_64 relocation in eh_frame would previously crash LLD
+# REQUIRES: mips
+# RUN: llvm-mc -filetype=obj -triple=mips64-unknown-freebsd %s -o %t.o
+# RUN: llvm-readobj -r %t.o | FileCheck %s -check-prefix OBJ
+# RUN: ld.lld --eh-frame-hdr -shared -z notext -o %t.so %t.o
+# RUN: llvm-readobj -r %t.so | FileCheck %s -check-prefix PIC-RELOCS
+
+# Linking this as a PIE executable would also previously crash
+# RUN: llvm-mc -filetype=obj -triple=mips64-unknown-freebsd %S/Inputs/archive2.s -o %t-foo.o
+# -pie needs -z notext because of the R_MIPS_64 relocation
+# RUN: ld.lld --eh-frame-hdr -Bdynamic -pie -z notext -o %t-pie-dynamic.exe %t.o %t-foo.o
+# RUN: llvm-readobj -r %t-pie-dynamic.exe | FileCheck %s -check-prefix PIC-RELOCS
+
+
+# OBJ:       Section ({{.*}}) .rela.text {
+# OBJ-NEXT:    0x0 R_MIPS_GPREL16/R_MIPS_SUB/R_MIPS_HI16 foo 0x0
+# OBJ-NEXT:  }
+# OBJ-NEXT:  Section ({{.*}}) .rela.eh_frame {
+# OBJ-NEXT:    0x1C R_MIPS_64/R_MIPS_NONE/R_MIPS_NONE .text 0x0
+# OBJ-NEXT:  }
+
+# PIC-RELOCS: Relocations [
+# PIC-RELOCS-NEXT:  Section (7) .rela.dyn {
+# PIC-RELOCS-NEXT:    {{0x.+}} R_MIPS_REL32/R_MIPS_64/R_MIPS_NONE - 0x10000
+# PIC-RELOCS-NEXT:  }
+# PIC-RELOCS-NEXT:]
+
+
+.globl foo
+
+bar:
+.cfi_startproc
+lui  $11, %hi(%neg(%gp_rel(foo)))
+.cfi_endproc
+
+.globl __start
+__start:
+b bar