[ELF] Reapply r254031 - LinkerScript: lookup absolute paths under sysroot

In case a sysroot prefix is configured, and the filename starts with
the '/' character, and the script being processed was located inside
the sysroot prefix, the file's name will be looked for in the sysroot
prefix. Otherwise, the linker falls to the common lookup scheme.

It is slightly modified version of the commit r254031. The problem of
the initial commit was in the `is_absolute` call. On Windows 'C:\' is
absolute path but we do not need to find it under sysroot. In this patch
linker looks up a path under sysroot only if the paths starts with '/'
character.

llvm-svn: 254135

lld/ELF/LinkerScript.cpp

@@ -28,8 +28,8 @@ using namespace lld::elf2;
 namespace {
 class LinkerScript {
 public:
-  LinkerScript(BumpPtrAllocator *A, StringRef S)
-      : Saver(*A), Tokens(tokenize(S)) {}
+  LinkerScript(BumpPtrAllocator *A, StringRef S, bool B)
+      : Saver(*A), Tokens(tokenize(S)), IsUnderSysroot(B) {}
   void run();
 
 private:
@@ -58,6 +58,7 @@ private:
   StringSaver Saver;
   std::vector<StringRef> Tokens;
   size_t Pos = 0;
+  bool IsUnderSysroot;
 };
 }
 
@@ -160,6 +161,15 @@ void LinkerScript::expect(StringRef Expect) {
 }
 
 void LinkerScript::addFile(StringRef S) {
+  if (IsUnderSysroot && S.startswith("/")) {
+    SmallString<128> Path;
+    (Config->Sysroot + S).toStringRef(Path);
+    if (sys::fs::exists(Path)) {
+      Driver->addFile(Saver.save(Path.str()));
+      return;
+    }
+  }
+
   if (sys::path::is_absolute(S)) {
     Driver->addFile(S);
   } else if (S.startswith("=")) {
@@ -290,7 +300,17 @@ void LinkerScript::readOutputSectionDescription() {
   }
 }
 
+static bool isUnderSysroot(StringRef Path) {
+  if (Config->Sysroot == "")
+    return false;
+  for (; !Path.empty(); Path = sys::path::parent_path(Path))
+    if (sys::fs::equivalent(Config->Sysroot, Path))
+      return true;
+  return false;
+}
+
 // Entry point. The other functions or classes are private to this file.
 void lld::elf2::readLinkerScript(BumpPtrAllocator *A, MemoryBufferRef MB) {
-  LinkerScript(A, MB.getBuffer()).run();
+  StringRef Path = MB.getBufferIdentifier();
+  LinkerScript(A, MB.getBuffer(), isUnderSysroot(Path)).run();
 }

lld/test/ELF/linkerscript.s

@@ -38,6 +38,13 @@
 # RUN: ld.lld -o %t2 %t.script -L%t.dir
 # RUN: llvm-readobj %t2 > /dev/null
 
+# RUN: echo "GROUP(" %t /libxyz.a ")" > %t.script
+# RUN: echo "GROUP(" %t /libxyz.a ")" > %t.dir/xyz.script
+# RUN: not ld.lld -o %t2 %t.script
+# RUN: not ld.lld -o %t2 %t.script --sysroot=%t.dir
+# RUN: ld.lld -o %t2 %t.dir/xyz.script --sysroot=%t.dir
+# RUN: llvm-readobj %t2 > /dev/null
+
 # RUN: echo "GROUP(" %t.script2 ")" > %t.script1
 # RUN: echo "GROUP(" %t ")" > %t.script2
 # RUN: ld.lld -o %t2 %t.script1