[lld-macho] Implement -oso_prefix

https://bugs.llvm.org/show_bug.cgi?id=50229

Differential Revision: https://reviews.llvm.org/D112291

Author: oontvoo

lld/MachO/Config.h

@@ -174,6 +174,8 @@ struct Configuration {
 
   bool zeroModTime = false;
 
+  llvm::StringRef osoPrefix;
+
   llvm::MachO::Architecture arch() const { return platformInfo.target.Arch; }
 
   llvm::MachO::PlatformKind platform() const {

lld/MachO/Driver.cpp

@@ -1095,6 +1095,29 @@ bool macho::link(ArrayRef<const char *> argsArr, bool canExitEarly,
   depTracker =
       make<DependencyTracker>(args.getLastArgValue(OPT_dependency_info));
 
+  config->osoPrefix = args.getLastArgValue(OPT_oso_prefix);
+  if (!config->osoPrefix.empty()) {
+    // Expand special characters, such as ".", "..", or  "~", if present.
+    // Note: LD64 only expands "." and not other special characters.
+    // That seems silly to imitate so we will not try to follow it, but rather
+    // just use real_path() to do it.
+
+    // The max path length is 4096, in theory. However that seems quite long
+    // and seems unlikely that any one would want to strip everything from the
+    // path. Hence we've picked a reasonably large number here.
+    SmallString<1024> expanded;
+    if (!fs::real_path(config->osoPrefix, expanded,
+                       /*expand_tilde=*/true)) {
+      // Note: LD64 expands "." to be `<current_dir>/`
+      // (ie., it has a slash suffix) whereas real_path() doesn't.
+      // So we have to append '/' to be consistent.
+      StringRef sep = sys::path::get_separator();
+      if (config->osoPrefix.equals(".") && !expanded.endswith(sep))
+        expanded += sep;
+      config->osoPrefix = saver.save(expanded.str());
+    }
+  }
+
   // Must be set before any InputSections and Symbols are created.
   config->deadStrip = args.hasArg(OPT_dead_strip);
 

lld/MachO/Options.td

@@ -576,7 +576,6 @@ def non_global_symbols_no_strip_list : Separate<["-"], "non_global_symbols_no_st
 def oso_prefix : Separate<["-"], "oso_prefix">,
     MetaVarName<"<path>">,
     HelpText<"Remove the prefix <path> from OSO symbols in the debug map">,
-    Flags<[HelpHidden]>,
     Group<grp_symtab>;
 def add_ast_path : Separate<["-"], "add_ast_path">,
     MetaVarName<"<path>">,

lld/MachO/SyntheticSections.cpp

@@ -860,7 +860,10 @@ void SymtabSection::emitObjectFileStab(ObjFile *file) {
   if (!file->archiveName.empty())
     path.append({"(", file->getName(), ")"});
 
-  stab.strx = stringTableSection.addString(saver.save(path.str()));
+  StringRef adjustedPath = saver.save(path.str());
+  adjustedPath.consume_front(config->osoPrefix);
+
+  stab.strx = stringTableSection.addString(adjustedPath);
   stab.desc = 1;
   stab.value = file->modTime;
   stabs.emplace_back(std::move(stab));

lld/test/MachO/stabs.s

@@ -50,6 +50,17 @@
 # RUN:   FileCheck %s -DDIR=%t -DFOO_PATH=%t/foo.o \
 # RUN:       -D#TEST_TIME=0x10 -D#FOO_TIME=0x20
 
+## Check that we emit relative path to object files in OSO entries
+## when -oso_prefix <path> is used.
+# RUN: cd %t && %lld -lSystem test.o foo.o no-debug.o -oso_prefix "%t" -o %t/test-rel
+# RUN: dsymutil -s  %t/test-rel | grep 'N_OSO' | FileCheck %s  -D#TEST_TIME=0x10 -D#FOO_TIME=0x20 --check-prefix=REL-PATH 
+# RUN: cd %t && %lld -lSystem test.o foo.o no-debug.o -oso_prefix "." -o %t/test-rel-dot
+# RUN: dsymutil -s  %t/test-rel-dot | grep 'N_OSO' | FileCheck %s  -D#TEST_TIME=0x10 -D#FOO_TIME=0x20 --check-prefix=REL-DOT 
+## Set HOME to %t (for ~ to expand to)
+# RUN: cd %t && env HOME=%t %lld -lSystem test.o foo.o no-debug.o -oso_prefix "~" -o %t/test-rel-tilde
+# RUN: dsymutil -s  %t/test-rel-tilde | grep 'N_OSO' | FileCheck %s  -D#TEST_TIME=0x10 -D#FOO_TIME=0x20 --check-prefix=REL-PATH
+
+
 # RUN: cd %t && %lld -lSystem test.o foo.a no-debug.o -o %t/test
 # RUN: (llvm-objdump --section-headers %t/test; dsymutil -s %t/test) | \
 # RUN:   FileCheck %s -DDIR=%t -DFOO_PATH=%t/foo.a\(foo.o\) \
@@ -65,6 +76,8 @@
 
 # CHECK:      (N_SO         ) 00                         0000   0000000000000000   '/tmp/test.cpp'
 # CHECK-NEXT: (N_OSO        ) 03                         0001   [[#%.16x,TEST_TIME]] '[[DIR]]/test.o'
+# REL-PATH:   (N_OSO        ) 03                         0001   [[#%.16x,TEST_TIME]] '/test.o'
+# REL-DOT:    (N_OSO        ) 03                         0001   [[#%.16x,TEST_TIME]] 'test.o'        
 # CHECK-NEXT: (N_STSYM      ) [[#%.2d,MORE_DATA_ID + 1]] 0000   [[#%.16x,STATIC:]] '_static_var'
 # CHECK-NEXT: (N_FUN        ) [[#%.2d,TEXT_ID + 1]]      0000   [[#%.16x,MAIN:]]   '_main'
 # CHECK-NEXT: (N_FUN        ) 00                         0000   0000000000000006{{$}}
@@ -87,6 +100,8 @@
 # CHECK-NEXT: (N_SO         ) 01                         0000   0000000000000000{{$}}
 # CHECK-NEXT: (N_SO         ) 00                         0000   0000000000000000   '/foo.cpp'
 # CHECK-NEXT: (N_OSO        ) 03                         0001   [[#%.16x,FOO_TIME]] '[[FOO_PATH]]'
+# REL-PATH-NEXT:   (N_OSO        ) 03                         0001   [[#%.16x,FOO_TIME]] '/foo.o'
+# REL-DOT-NEXT:    (N_OSO        ) 03                         0001   [[#%.16x,FOO_TIME]] 'foo.o'
 # CHECK-NEXT: (N_FUN        ) [[#%.2d,TEXT_ID + 1]]      0000   [[#%.16x,FOO:]]    '_foo'
 # CHECK-NEXT: (N_FUN        ) 00                         0000   0000000000000001{{$}}
 # CHECK-NEXT: (N_SO         ) 01                         0000   0000000000000000{{$}}