[dsymutil] Fix handling of aliases to private external symbols

[JDevlieghere]

Summary

dsymutil was incorrectly ignoring aliases to private extern symbols in the MachODebugMapParser. This resulted in spurious warnings about not being able to find symbols.

rdar://49652389

[friss]

LGTM

[aprantl]

llvm/tools/dsymutil/MachODebugMapParser.cpp

564

bool AliasToPrivateExternal = (SymType & MachO::N_PEXT);
if ((Section == MainBinary.section_end() || Section->isText()) && ! AliasToPrivateExternal)

?

llvm/test/tools/dsymutil/ARM/private-extern-alias.test

+$ cat private_extern.c
+__attribute__((visibility("hidden")))
+int* foo() {
+  int i = 10;
+  volatile int* j = &i;
+  return j;
+}
+
+int* bar() {
+  return foo();
+}
+
+$ cat main.c
+int* bar();
+int main() {
+  return *bar();
+}
+
+$ cat alias_list
+_foo _baz
+
+$ xcrun --sdk iphoneos clang -g private_extern.c -c -o private_extern.o -target arm64-apple-ios14.0
+$ xcrun --sdk iphoneos clang -g main.c -c -o main.o -target arm64-apple-ios14.0
+$ xcrun --sdk iphoneos clang private_extern.o main.o -target arm64-apple-ios14.0 -o private_extern.out -Xlinker -alias_list -Xlinker alias_list
+
+RUN: dsymutil -oso-prepend-path %p/../Inputs %p/../Inputs/private/tmp/private_extern/private_extern.out -o %t.dSYM --verbose 2>&1 | FileCheck %s
+CHECK-NOT: could not find object file symbol for symbol _baz
+CHECK: { sym: _foo, objAddr: 0x0000000000000000, binAddr: 0x0000000100007F58, size: 0x00000020 }
+CHECK: { sym: _baz, objAddr: 0x0000000000000000, binAddr: 0x0000000100007F58, size: 0x00000000 }

llvm/tools/dsymutil/MachODebugMapParser.cpp

uint8_t SymType =
         MainBinary.getSymbolTableEntry(Sym.getRawDataRefImpl()).n_type;
     bool Extern = SymType & (MachO::N_EXT | MachO::N_PEXT);
     Expected<section_iterator> SectionOrErr = Sym.getSection();
     if (!SectionOrErr) {
       // TODO: Actually report errors helpfully.
       consumeError(SectionOrErr.takeError());
       continue;
     }
     Section = *SectionOrErr;
-    if (Section == MainBinary.section_end() || Section->isText())
+    if ((Section == MainBinary.section_end() || Section->isText()) &&
+        !(SymType &
+          MachO::N_PEXT)) // Alias to non-external (was a private external)
       continue;
     uint64_t Addr = cantFail(Sym.getValue());
     Expected<StringRef> NameOrErr = Sym.getName();
     if (!NameOrErr) {
       // TODO: Actually report errors helpfully.
       consumeError(NameOrErr.takeError());
       continue;
     }