ELF: The later of --build-id and --build-id= wins.

[pcc]

Summary

If the compiler driver passes --build-id and the user uses -Wl to
pass --build-id= then the user's flag should take precedence.

[pcc]

lld/ELF/Driver.cpp

576

Sorry, need a null check here. I'll upload a new patch.

[pcc]

• Add null check

[ruiu]

LGTM

lld/ELF/Driver.cpp

static std::pair<bool, bool> getHashStyle(opt::InputArgList &Args) {
   return {true, true};
 }
 
 // Parse --build-id or --build-id=<style>. We handle "tree" as a
 // synonym for "sha1" because all our hash functions including
 // -build-id=sha1 are actually tree hashes for performance reasons.
 static std::pair<BuildIdKind, std::vector<uint8_t>>
 getBuildId(opt::InputArgList &Args) {
-  if (Args.hasArg(OPT_build_id))
+  auto *Arg = Args.getLastArg(OPT_build_id, OPT_build_id_eq);
+  if (Arg->getOption().getID() == OPT_build_id)
     return {BuildIdKind::Fast, {}};
 
-  StringRef S = getString(Args, OPT_build_id_eq, "none");
+  StringRef S = Arg->getValue();
   if (S == "md5")
     return {BuildIdKind::Md5, {}};
   if (S == "sha1" || S == "tree")
     return {BuildIdKind::Sha1, {}};
   if (S == "uuid")
     return {BuildIdKind::Uuid, {}};
   if (S.startswith("0x"))
     return {BuildIdKind::Hexstring, parseHex(S.substr(2))};

lld/test/ELF/build-id.s

 # RUN: ld.lld --build-id=0x12345678 %t -o %t2
 # RUN: llvm-objdump -s %t2 | FileCheck -check-prefix=HEX %s
 
 # RUN: ld.lld %t -o %t2
 # RUN: llvm-objdump -s %t2 | FileCheck -check-prefix=NONE %s
 
 # RUN: ld.lld --build-id=md5 --build-id=none %t -o %t2
 # RUN: llvm-objdump -s %t2 | FileCheck -check-prefix=NONE %s
+# RUN: ld.lld --build-id --build-id=none %t -o %t2 -no-threads
+# RUN: llvm-objdump -s %t2 | FileCheck -check-prefix=NONE %s
+# RUN: ld.lld --build-id=none --build-id %t -o %t2 -no-threads
+# RUN: llvm-objdump -s %t2 | FileCheck -check-prefix=DEFAULT %s
 
 .globl _start
 _start:
   nop
 
 .section .note.test, "a", @note
    .quad 42