[LTO/gold] Support --wrap

Summary:
(Restores r327459 with handling for old plugin-api.h)
Utilize new gold plugin api interface for obtaining --wrap option
arguments, and LTO API handling (added for --wrap support in lld LTO),
to mark symbols so that LTO does not optimize them inappropriately.

Note the test cases will be in a new gold test subdirectory that
is dependent on the next release of gold which will contain the new
interfaces.

Reviewers: pcc, tmsriram

Subscribers: mehdi_amini, llvm-commits, inglorion

Differential Revision: https://reviews.llvm.org/D44235

llvm-svn: 327506

test/tools/gold/X86/v1.16/Inputs/wrap-bar.ll

@@ -0,0 +1,14 @@
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+define hidden void @bar() {
+  ret void
+}
+
+define hidden void @__real_bar() {
+  ret void
+}
+
+define hidden void @__wrap_bar() {
+  ret void
+}

test/tools/gold/X86/v1.16/lit.local.cfg

@@ -0,0 +1,28 @@
+import re
+import subprocess
+
+def is_gold_v1_16_linker_available():
+
+  if not config.gold_executable:
+    return False
+  try:
+    ld_cmd = subprocess.Popen([config.gold_executable, '-v'],
+                              stdout = subprocess.PIPE,
+                              stderr = subprocess.PIPE)
+    ld_out, _ = ld_cmd.communicate()
+    ld_out = ld_out.decode()
+  except:
+    return False
+
+  match = re.search(r'GNU gold \(.*\) (\d+)\.(\d+)', ld_out)
+  if not match:
+    return False
+  major = int(match.group(1))
+  minor = int(match.group(2))
+  if major < 1 or (major == 1 and minor < 16):
+    return False
+
+  return True
+
+if not is_gold_v1_16_linker_available():
+  config.unsupported = True

test/tools/gold/X86/v1.16/wrap-1.ll

@@ -0,0 +1,42 @@
+; LTO
+; RUN: llvm-as %s -o %t.o
+; RUN: %gold -plugin %llvmshlibdir/LLVMgold%shlibext %t.o -o %t.out -wrap=bar -plugin-opt=save-temps
+; RUN: llvm-readobj -t %t.out | FileCheck %s
+; RUN: cat %t.out.resolution.txt | FileCheck -check-prefix=RESOLS %s
+
+; ThinLTO
+; RUN: opt -module-summary %s -o %t.o
+; RUN: %gold -plugin %llvmshlibdir/LLVMgold%shlibext %t.o -o %t.out -wrap=bar -plugin-opt=save-temps
+; RUN: llvm-readobj -t %t.out | FileCheck %s
+; RUN: cat %t.out.resolution.txt | FileCheck -check-prefix=RESOLS %s
+
+; CHECK:      Name: __wrap_bar
+; CHECK-NEXT: Value:
+; CHECK-NEXT: Size:
+; CHECK-NEXT: Binding: Global
+; CHECK-NEXT: Type: Function
+
+; Make sure that the 'r' (linker redefined) bit is set for bar and __real_bar
+; in the resolutions file, and that the 'x' (visible to regular obj) bit is set
+; for bar and __wrap_bar.
+; RESOLS: ,bar,lxr
+; RESOLS: ,__wrap_bar,plx
+; RESOLS: ,__real_bar,plr
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+declare void @bar()
+
+define void @_start() {
+  call void @bar()
+  ret void
+}
+
+define void @__wrap_bar() {
+  ret void
+}
+
+define void @__real_bar() {
+  ret void
+}

test/tools/gold/X86/v1.16/wrap-2.ll

@@ -0,0 +1,55 @@
+; LTO
+; This doesn't currently work with gold, because it does not apply defsym
+; renaming to symbols in the same module (apparently by design for consistency
+; with GNU ld). Because regular LTO hands back a single object file to gold,
+; it doesn't perform the desired defsym renaming. This isn't an issue with
+; ThinLTO which hands back multiple native objects to gold. For regular
+; LTO defsym handling, gold will need a fix (not the gold plugin).
+; RUN-TODO: llvm-as %s -o %t.o
+; RUN-TODO: llvm-as %S/Inputs/wrap-bar.ll -o %t1.o
+; RUN-TODO: %gold -plugin %llvmshlibdir/LLVMgold%shlibext %t.o %t1.o -shared -o %t.so -wrap=bar
+; RUN-TODO: llvm-objdump -d %t.so | FileCheck %s
+; RUN-TODO: llvm-readobj -t %t.so | FileCheck -check-prefix=BIND %s
+
+; ThinLTO
+; RUN: opt -module-summary %s -o %t.o
+; RUN: opt -module-summary %S/Inputs/wrap-bar.ll -o %t1.o
+; RUN: %gold -plugin %llvmshlibdir/LLVMgold%shlibext %t.o %t1.o -shared -o %t.so -wrap=bar
+; RUN: llvm-objdump -d %t.so | FileCheck %s -check-prefix=THIN
+; RUN: llvm-readobj -t %t.so | FileCheck -check-prefix=BIND %s
+
+; Make sure that calls in foo() are not eliminated and that bar is
+; routed to __wrap_bar and __real_bar is routed to bar.
+
+; CHECK:      foo:
+; CHECK-NEXT: pushq	%rax
+; CHECK-NEXT: callq{{.*}}<__wrap_bar>
+; CHECK-NEXT: callq{{.*}}<bar>
+
+; THIN:      foo:
+; THIN-NEXT: pushq	%rax
+; THIN-NEXT: callq{{.*}}<__wrap_bar>
+; THIN-NEXT: popq  %rax
+; THIN-NEXT: jmp{{.*}}<bar>
+
+; Check that bar and __wrap_bar retain their original binding.
+; BIND:      Name: bar
+; BIND-NEXT: Value:
+; BIND-NEXT: Size:
+; BIND-NEXT: Binding: Local
+; BIND:      Name: __wrap_bar
+; BIND-NEXT: Value:
+; BIND-NEXT: Size:
+; BIND-NEXT: Binding: Local
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+declare void @bar()
+declare void @__real_bar()
+
+define void @foo() {
+  call void @bar()
+  call void @__real_bar()
+  ret void
+}

tools/gold/gold-plugin.cpp

@@ -44,9 +44,18 @@
 
 #define LDPT_GET_SYMBOLS_V3 28
 
+// FIXME: Remove when binutils 2.31 (containing gold 1.16) is the minimum
+// required version.
+#define LDPT_GET_WRAP_SYMBOLS 32
+
 using namespace llvm;
 using namespace lto;
 
+// FIXME: Remove when binutils 2.31 (containing gold 1.16) is the minimum
+// required version.
+typedef enum ld_plugin_status (*ld_plugin_get_wrap_symbols)(
+    uint64_t *num_symbols, const char ***wrap_symbol_list);
+
 static ld_plugin_status discard_message(int level, const char *format, ...) {
   // Die loudly. Recent versions of Gold pass ld_plugin_message as the first
   // callback in the transfer vector. This should never be called.
@@ -56,6 +65,7 @@ static ld_plugin_status discard_message(int level, const char *format, ...) {
 static ld_plugin_release_input_file release_input_file = nullptr;
 static ld_plugin_get_input_file get_input_file = nullptr;
 static ld_plugin_message message = discard_message;
+static ld_plugin_get_wrap_symbols get_wrap_symbols = nullptr;
 
 namespace {
 struct claimed_file {
@@ -93,6 +103,8 @@ struct PluginInputFile {
 struct ResolutionInfo {
   bool CanOmitFromDynSym = true;
   bool DefaultVisibility = true;
+  bool CanInline = true;
+  bool IsUsedInRegularObj = false;
 };
 
 }
@@ -367,6 +379,13 @@ ld_plugin_status onload(ld_plugin_tv *tv) {
     case LDPT_MESSAGE:
       message = tv->tv_u.tv_message;
       break;
+    case LDPT_GET_WRAP_SYMBOLS:
+      // FIXME: When binutils 2.31 (containing gold 1.16) is the minimum
+      // required version, this should be changed to:
+      // get_wrap_symbols = tv->tv_u.tv_get_wrap_symbols;
+      get_wrap_symbols =
+          (ld_plugin_get_wrap_symbols)tv->tv_u.tv_register_new_input;
+      break;
     default:
       break;
     }
@@ -563,6 +582,29 @@ static ld_plugin_status claim_file_hook(const ld_plugin_input_file *file,
     }
   }
 
+  // Handle any --wrap options passed to gold, which are than passed
+  // along to the plugin.
+  if (get_wrap_symbols) {
+    const char **wrap_symbols;
+    uint64_t count = 0;
+    if (get_wrap_symbols(&count, &wrap_symbols) != LDPS_OK) {
+      message(LDPL_ERROR, "Unable to get wrap symbols!");
+      return LDPS_ERR;
+    }
+    for (uint64_t i = 0; i < count; i++) {
+      StringRef Name = wrap_symbols[i];
+      ResolutionInfo &Res = ResInfo[Name];
+      ResolutionInfo &WrapRes = ResInfo["__wrap_" + Name.str()];
+      ResolutionInfo &RealRes = ResInfo["__real_" + Name.str()];
+      // Tell LTO not to inline symbols that will be overwritten.
+      Res.CanInline = false;
+      RealRes.CanInline = false;
+      // Tell LTO not to eliminate symbols that will be used after renaming.
+      Res.IsUsedInRegularObj = true;
+      WrapRes.IsUsedInRegularObj = true;
+    }
+  }
+
   return LDPS_OK;
 }
 
@@ -686,6 +728,12 @@ static void addModule(LTO &Lto, claimed_file &F, const void *View,
         (IsExecutable || !Res.DefaultVisibility))
       R.FinalDefinitionInLinkageUnit = true;
 
+    if (!Res.CanInline)
+      R.LinkerRedefined = true;
+
+    if (Res.IsUsedInRegularObj)
+      R.VisibleToRegularObj = true;
+
     freeSymName(Sym);
   }