[llvm] [BOLT] Account for stubs with symbols in plt (PR #192716)

[Hemant Kulkarni via llvm-commits]

https://github.com/awshkulkar updated https://github.com/llvm/llvm-project/pull/192716

>From afa49809d96c8d5137fbcaf0245ce559865893f9 Mon Sep 17 00:00:00 2001
From: Hemant Kulkarni <hkulkar at amazon.com>
Date: Fri, 3 Apr 2026 15:07:11 +0000
Subject: [PATCH] [bolt] Account for stubs with symbols in plt.

LLD and bfd do not generate functions symbols for stubs
in PLT. However, mold does and trips the object discovery
to create two functions (BF then PLTFunc). This can cause
symbol to be resoved with BF with incorrect ADRP immediate field in
AArch64.
---
 bolt/lib/Rewrite/RewriteInstance.cpp      |  7 +++--
 bolt/test/AArch64/plt-mold-func-symbols.s | 36 +++++++++++++++++++++++
 bolt/test/X86/plt-mold.test               |  2 +-
 3 files changed, 42 insertions(+), 3 deletions(-)
 create mode 100644 bolt/test/AArch64/plt-mold-func-symbols.s

diff --git a/bolt/lib/Rewrite/RewriteInstance.cpp b/bolt/lib/Rewrite/RewriteInstance.cpp
index 43d4421e06928..10326f89671e1 100644
--- a/bolt/lib/Rewrite/RewriteInstance.cpp
+++ b/bolt/lib/Rewrite/RewriteInstance.cpp
@@ -1041,8 +1041,11 @@ void RewriteInstance::discoverFileObjects() {
 
     FileSymRefs.emplace(SymbolAddress, Symbol);
 
-    // Skip section symbols that will be registered by disassemblePLT().
-    if (SymbolType == SymbolRef::ST_Debug) {
+    // Skip symbols in PLT sections that will be registered by disassemblePLT().
+    // ST_Debug covers section markers (lld/GNU ld), ST_Function covers
+    // explicit stub symbols emitted by mold (e.g., malloc$plt).
+    if (SymbolType == SymbolRef::ST_Debug ||
+        SymbolType == SymbolRef::ST_Function) {
       ErrorOr<BinarySection &> BSection =
           BC->getSectionForAddress(SymbolAddress);
       if (BSection && getPLTSectionInfo(BSection->getName()))
diff --git a/bolt/test/AArch64/plt-mold-func-symbols.s b/bolt/test/AArch64/plt-mold-func-symbols.s
new file mode 100644
index 0000000000000..3c710ae23d48b
--- /dev/null
+++ b/bolt/test/AArch64/plt-mold-func-symbols.s
@@ -0,0 +1,36 @@
+## Test that BOLT correctly handles mold-style STT_FUNC symbols in PLT
+## sections.
+
+# REQUIRES: system-linux
+
+## Build a shared library from the common stubs.
+# RUN: %clang %cflags %p/../Inputs/stub.c -fPIC -shared -o %t.so
+
+## Build and link the main binary. The linker creates a real PLT entry.
+# RUN: llvm-mc -filetype=obj -triple aarch64-linux %s -o %t.o
+# RUN: ld.lld -pie %t.o %t.so -o %t.exe --emit-relocs
+
+## Inject a mold-style STT_FUNC symbol at the PLT entry for printf.
+## Mold places "printf$plt" directly on the PLT stub; we simulate this
+## with llvm-objcopy. The PLT header is 32 bytes on AArch64, and each
+## entry is 16 bytes. printf is the only entry after the header.
+# RUN: llvm-objcopy --add-symbol "printf\$plt=.plt:32,function,local" \
+# RUN:   %t.exe %t
+
+## Verify BOLT resolves the call as printf at PLT, not printf$plt.
+# RUN: llvm-bolt %t -o %t.bolt --print-cfg --print-only=_start 2>&1 \
+# RUN:   | FileCheck %s
+# RUN: llvm-readobj --syms %t.bolt | grep -A7 printf$plt | FileCheck \
+# RUN:   %s --check-prefix=CHECK-SYM
+
+# CHECK:     bl printf at PLT
+# CHECK-NOT: printf$plt
+# CHECK-SYM: Section: .plt
+
+  .text
+  .globl _start
+  .type _start, %function
+_start:
+  bl printf
+  ret
+  .size _start, .-_start
diff --git a/bolt/test/X86/plt-mold.test b/bolt/test/X86/plt-mold.test
index 75c8c023cf3c2..8ef21e87b3453 100644
--- a/bolt/test/X86/plt-mold.test
+++ b/bolt/test/X86/plt-mold.test
@@ -3,4 +3,4 @@
 
 ## 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
+CHECK:  callq printf at PLT