[lld] Infer relocation model from module flags in relocatable LTO link

[eugenis]

Summary

Fix for PR33096.

[davide]

test/ELF/lto/relocation-model-pic.ll

3–6 ↗

(On Diff #99650)

can't this be a separate input in living in Inputs/ ?

[eugenis]

test/ELF/lto/relocation-model-pic.ll

3–6 ↗

(On Diff #99650)

It can, but then the reader has to go and find this other file to understand what's going on in the test...
I can do it if you feel strongly about it.

[davide]

ELF/LTO.cpp

76–82

I'll leave the final decision to @ruiu, but I feel

if ()
  [...]
else if()
  [...]
 else()

would be more readable in this case.
Not strong about this one either :)

test/ELF/lto/relocation-model-pic.ll

3–6 ↗

(On Diff #99650)

Not necessarily, but this is generally what's done elsewhere in lld, so I'd keep it like that for consistency.

[ruiu]

ELF/LTO.cpp

76–82

I was about to say the same. :)

[davide]

LGTM. I see Peter confirmed this is the correct fix in the PR, and I think so too.

[eugenis]

r303579

ELF/LTO.cpp

 
 static std::unique_ptr<lto::LTO> createLTO() {
   lto::Config Conf;
 
   // LLD supports the new relocations.
   Conf.Options = InitTargetOptionsFromCodeGenFlags();
   Conf.Options.RelaxELFRelocations = true;
 
-  Conf.RelocModel = Config->Pic ? Reloc::PIC_ : Reloc::Static;
+  if (Config->Relocatable)
+    Conf.RelocModel = None;
+  else if (Config->Pic)
+    Conf.RelocModel = Reloc::PIC_;
+  else
+    Conf.RelocModel = Reloc::Static;
   Conf.CodeModel = GetCodeModelFromCMModel();
   Conf.DisableVerify = Config->DisableVerify;
   Conf.DiagHandler = diagnosticHandler;
   Conf.OptLevel = Config->LTOO;
 
   // Set up a custom pipeline if we've been asked to.
   Conf.OptPipeline = Config->LTONewPmPasses;
   Conf.AAPipeline = Config->LTOAAPipeline;
 

test/ELF/lto/Inputs/relocation-model-pic.ll

+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+@foo = external global i32
+define i32 @main() {
+  %t = load i32, i32* @foo
+  ret i32 %t
+}
+
+!llvm.module.flags = !{!0}
+!0 = !{i32 1, !"PIC Level", i32 2}

test/ELF/lto/relocation-model.ll

+; REQUIRES: x86
+
+; RUN: llvm-as %s -o %t.o
+; RUN: llvm-as %p/Inputs/relocation-model-pic.ll -o %t.pic.o
+
+;; Non-PIC source.
+
+; RUN: ld.lld %t.o -o %t-out -save-temps -shared
+; RUN: llvm-readobj -r %t-out.lto.o | FileCheck %s --check-prefix=PIC
+
+; RUN: ld.lld %t.o -o %t-out -save-temps --export-dynamic --noinhibit-exec -pie
+; RUN: llvm-readobj -r %t-out.lto.o | FileCheck %s --check-prefix=PIC
+
+; RUN: ld.lld %t.o -o %t-out -save-temps --export-dynamic --noinhibit-exec
+; RUN: llvm-readobj -r %t-out.lto.o | FileCheck %s --check-prefix=STATIC
+
+; RUN: ld.lld %t.o -o %t-out -save-temps -r --export-dynamic
+; RUN: llvm-readobj -r %t-out.lto.o | FileCheck %s --check-prefix=STATIC
+
+
+;; PIC source.
+
+; RUN: ld.lld %t.pic.o -o %t-out -save-temps -shared
+; RUN: llvm-readobj -r %t-out.lto.o | FileCheck %s --check-prefix=PIC
+
+; RUN: ld.lld %t.pic.o -o %t-out -save-temps --export-dynamic --noinhibit-exec -pie
+; RUN: llvm-readobj -r %t-out.lto.o | FileCheck %s --check-prefix=PIC
+
+; RUN: ld.lld %t.pic.o -o %t-out -save-temps --export-dynamic --noinhibit-exec
+; RUN: llvm-readobj -r %t-out.lto.o | FileCheck %s --check-prefix=STATIC
+
+; RUN: ld.lld %t.pic.o -o %t-out -save-temps -r --export-dynamic
+; RUN: llvm-readobj -r %t-out.lto.o | FileCheck %s --check-prefix=PIC
+
+
+; PIC: R_X86_64_REX_GOTPCRELX foo
+; STATIC: R_X86_64_PC32 foo
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+@foo = external global i32
+define i32 @main() {
+  %t = load i32, i32* @foo
+  ret i32 %t
+}