[BOLT] Add mold-style PLT support

mold linker creates symbols for PLT entries and that caught BOLT by
surprise. Add the support for marked PLT entries.

Fixes: #58498

Reviewed By: yota9

Differential Revision: https://reviews.llvm.org/D136655

3 files changed, 421 insertions, 9 deletions

diff --git a/bolt/lib/Rewrite/RewriteInstance.cpp b/bolt/lib/Rewrite/RewriteInstance.cpp
index ac83b6dd95d8..56d7868be73d 100644
--- a/bolt/lib/Rewrite/RewriteInstance.cpp
+++ b/bolt/lib/Rewrite/RewriteInstance.cpp
@@ -1277,9 +1277,12 @@ void RewriteInstance::createPLTBinaryFunction(uint64_t TargetAddress,
 
   ErrorOr<BinarySection &> Section = BC->getSectionForAddress(EntryAddress);
   assert(Section && "cannot get section for address");
-  BF = BC->createBinaryFunction(Rel->Symbol->getName().str() + "@PLT", *Section,
-                                EntryAddress, 0, EntrySize,
-                                Section->getAlignment());
+  if (!BF)
+    BF = BC->createBinaryFunction(Rel->Symbol->getName().str() + "@PLT",
+                                  *Section, EntryAddress, 0, EntrySize,
+                                  Section->getAlignment());
+  else
+    BF->addAlternativeName(Rel->Symbol->getName().str() + "@PLT");
   setPLTSymbol(BF, Rel->Symbol->getName());
 }
 
@@ -1411,15 +1414,19 @@ void RewriteInstance::disassemblePLT() {
       continue;
 
     analyzeOnePLTSection(Section, PLTSI->EntrySize);
-    // If we did not register any function at the start of the section,
-    // then it must be a general PLT entry. Add a function at the location.
-    if (BC->getBinaryFunctions().find(Section.getAddress()) ==
-        BC->getBinaryFunctions().end()) {
-      BinaryFunction *BF = BC->createBinaryFunction(
+
+    BinaryFunction *PltBF;
+    auto BFIter = BC->getBinaryFunctions().find(Section.getAddress());
+    if (BFIter != BC->getBinaryFunctions().end()) {
+      PltBF = &BFIter->second;
+    } else {
+      // If we did not register any function at the start of the section,
+      // then it must be a general PLT entry. Add a function at the location.
+      PltBF = BC->createBinaryFunction(
           "__BOLT_PSEUDO_" + Section.getName().str(), Section,
           Section.getAddress(), 0, PLTSI->EntrySize, Section.getAlignment());
-      BF->setPseudo(true);
     }
+    PltBF->setPseudo(true);
   }
 }
 
diff --git a/bolt/test/X86/Inputs/plt-mold.yaml b/bolt/test/X86/Inputs/plt-mold.yaml
new file mode 100644
index 000000000000..bc594db73663
--- /dev/null
+++ b/bolt/test/X86/Inputs/plt-mold.yaml
@@ -0,0 +1,399 @@
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diff --git a/bolt/test/X86/plt-mold.test b/bolt/test/X86/plt-mold.test
new file mode 100644
index 000000000000..75c8c023cf3c
--- /dev/null
+++ b/bolt/test/X86/plt-mold.test
@@ -0,0 +1,6 @@
+# RUN: yaml2obj %p/Inputs/plt-mold.yaml &> %t.exe
+# RUN: llvm-bolt %t.exe --print-cfg --print-only=main.* -o %t.out | FileCheck %s
+
+## Check that llvm-bolt correctly parses PLT created by mold linker.
+## The only call instruction in main() should be a call to printf() in PLT.
+CHECK:  callq "printf$plt