[lld-macho] Preserve the size of common symbols

[int3]

Summary

We never noticed this before because the only time the size gets emitted is via
the linker map...

[thakis]

😀

[thakis]

(out of interest, do you see common symbols in use in practice?)

[int3]

Just ran a link on a fairly large dylib and the addCommon code path wasn't hit at all. So I guess it's not super common. I just noticed this issue while writing the test for the map file...

lld/MachO/Driver.cpp

for (Symbol *sym : symtab->getSymbols()) {
     if (!osec)
       osec = ConcatOutputSection::getOrCreateForInput(isec);
     isec->parent = osec;
     inputSections.push_back(isec);
 
     // FIXME: CommonSymbol should store isReferencedDynamically, noDeadStrip
     // and pass them on here.
     replaceSymbol<Defined>(
-        sym, sym->getName(), common->getFile(), isec, /*value=*/0, /*size=*/0,
+        sym, sym->getName(), common->getFile(), isec, /*value=*/0, common->size,
         /*isWeakDef=*/false, /*isExternal=*/true, common->privateExtern,
         /*includeInSymtab=*/true, /*isThumb=*/false,
         /*isReferencedDynamically=*/false, /*noDeadStrip=*/false);
   }
 }
 
 static void initializeSectionRenameMap() {
   if (config->dataConst) {

lld/test/MachO/dead-strip.s

 # EXECDATA-DAG:   _no_dead_strip_globl
 # EXECDATA-DAG:   __mh_execute_header
 
 ## Check that dead stripped symbols get listed properly.
 # RUN: FileCheck --check-prefix=MAP %s < %t/map
 
 # MAP: _main
 # MAP-LABEL: Dead Stripped Symbols
-# MAP: <<dead>> 0x00000000 [ 1] _unref_com
+# MAP: <<dead>> 0x00000001 [ 1] _unref_com
 # MAP: <<dead>> 0x00000008 [ 1] _unref_data
 # MAP: <<dead>> 0x00000006 [ 1] _unref_extern
 # MAP: <<dead>> 0x00000001 [ 1] _unref_local
 # MAP: <<dead>> 0x00000007 [ 1] _unref_private_extern
 # MAP: <<dead>> 0x00000008 [ 1] l_unref_data
 
 ## Run dead stripping on code without any dead symbols.
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-macos \

lld/test/MachO/map-file.s

 # CHECK-NEXT: 0x[[#%X,TEXT]]  0x{{[0-9a-f]+}}   __TEXT   __text
 # CHECK-NEXT: 0x[[#%X,DATA]]  0x{{[0-9a-f]+}}   __TEXT   obj
 # CHECK-NEXT: 0x[[#%X,BSS]]   0x{{[0-9a-f]+}}   __DATA   __common
 
 # CHECK-NEXT: # Symbols:
 # CHECK-NEXT: # Address           Size        File   Name
 # CHECK-NEXT: 0x[[#%X,MAIN]]      0x00000001  [  1]  _main
 # CHECK-NEXT: 0x[[#%X,FOO]]       0x00000000  [  2]  _foo
-# CHECK-NEXT: 0x[[#%X,NUMBER]]    0x00000000  [  1]  _number
+# CHECK-NEXT: 0x[[#%X,NUMBER]]    0x00000001  [  1]  _number
 
 # RUN: %lld -map %t/c-string-literal-map %t/c-string-literal.o -o %t/c-string-literal-out
 # RUN: FileCheck --check-prefix=CSTRING %s < %t/c-string-literal-map
 
 ## C-string literals should be printed as "literal string: <C string literal>"
 # CSTRING-LABEL: Symbols:
 # CSTRING-DAG: _main
 # CSTRING-DAG: literal string: Hello world!\n