Avoid short relocation in x86_64 large code model

[sanxiyn]

Summary

http://llvm.org/bugs/show_bug.cgi?id=21423

[• rafael]

test/CodeGen/X86/code-model-eh-frame.ll

1

You should be able to test this with llvm-mc, no?

[sanxiyn]

test/CodeGen/X86/code-model-eh-frame.ll

1

Can I? My first try used llvm-mc, but when I asked on IRC, someone (sorry, I don't remember who) answered I must pass -code-model to llc, not llvm-mc.

[joerg]

lib/MC/MCObjectFileInfo.cpp

277

I'd prefer to do a positive check for Small and Medium. JIT for example likely wants to get sdata8 too.

[lhames]

Ping. Looks reasonable to me, but I'm not an ELF (or DWARF) expert. This like it would fix https://bugs.llvm.org//show_bug.cgi?id=21423, and part of https://bugs.llvm.org//show_bug.cgi?id=15356.

[joerg]

My point remains.

[RKSimon]

test/CodeGen/X86/code-model-eh-frame.ll

1

@rafael's comment still remains - why isn't this an MC test?

[echristo]

test/CodeGen/X86/code-model-eh-frame.ll

1

Agreed. You can do something like the following:

echristo@athyra ~/tmp> clang -S bar.c
echristo@athyra ~/tmp> llvm-mc -code-model=large bar.s -filetype=obj -o bar.o
echristo@athyra ~/tmp> llvm-objdump -r bar.o

bar.o: file format ELF64-x86-64

RELOCATION RECORDS FOR [.rela.eh_frame]:
0000000000000020 R_X86_64_PC64 Unknown

lib/MC/MCObjectFileInfo.cpp

void MCObjectFileInfo::InitELFMCObjectFileInfo(Triple T) {
   case Triple::mips:
   case Triple::mipsel:
     FDECFIEncoding = dwarf::DW_EH_PE_sdata4;
     break;
   case Triple::mips64:
   case Triple::mips64el:
     FDECFIEncoding = dwarf::DW_EH_PE_sdata8;
     break;
+  case Triple::x86_64:
+    FDECFIEncoding = dwarf::DW_EH_PE_pcrel |
+        (CMModel != CodeModel::Large
+         ? dwarf::DW_EH_PE_sdata4 : dwarf::DW_EH_PE_sdata8);
+    break;
   default:
     FDECFIEncoding = dwarf::DW_EH_PE_pcrel | dwarf::DW_EH_PE_sdata4;
     break;
   }
 
   switch (T.getArch()) {
   case Triple::arm:
   case Triple::armeb:

test/CodeGen/X86/code-model-eh-frame.ll

+; RUN: llc < %s -filetype=obj -code-model=small \
+; RUN:  | llvm-objdump -r - \
+; RUN:  | FileCheck -check-prefix SMALL %s
+; RUN: llc < %s -filetype=obj -code-model=large \
+; RUN:  | llvm-objdump -r - \
+; RUN:  | FileCheck -check-prefix LARGE %s
+
+; SMALL: R_X86_64_PC32
+; LARGE: R_X86_64_PC64
+
+target triple = "x86_64-unknown-linux-gnu"
+
+define void @test() {
+  ret void
+}