[llvm] [Bolt] fix a wrong relocation update issue with weak references (PR #69136)
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Tue Dec 5 02:17:45 PST 2023
https://github.com/linsinan1995 updated https://github.com/llvm/llvm-project/pull/69136
>From 6a25f55d949350890374fe17e8fce7059a3d0a3e Mon Sep 17 00:00:00 2001
From: Sinan Lin <sinan.lin at linux.alibaba.com>
Date: Mon, 16 Oct 2023 09:51:48 +0800
Subject: [PATCH] [BOLT] do not search for PLT entries if the relocation is
against a weak reference symbol.
Take a common weak reference pattern for example
```
__attribute__((weak)) void undef_weak_fun();
if (&undef_weak_fun)
undef_weak_fun();
```
In this case, an undefined weak symbol `undef_weak_fun` has an address
of zero, and Bolt incorrectly changes the relocation for the
corresponding symbol to symbol at PLT, leading to incorrect runtime
behavior.
---
bolt/lib/Rewrite/RewriteInstance.cpp | 11 ++-
.../AArch64/update-weak-reference-symbol.s | 77 +++++++++++++++++++
2 files changed, 87 insertions(+), 1 deletion(-)
create mode 100644 bolt/test/AArch64/update-weak-reference-symbol.s
diff --git a/bolt/lib/Rewrite/RewriteInstance.cpp b/bolt/lib/Rewrite/RewriteInstance.cpp
index 81c9cbff726bb..ea94d0d0a6551 100644
--- a/bolt/lib/Rewrite/RewriteInstance.cpp
+++ b/bolt/lib/Rewrite/RewriteInstance.cpp
@@ -2067,6 +2067,14 @@ bool RewriteInstance::analyzeRelocation(
if (!Relocation::isSupported(RType))
return false;
+ auto IsWeakReference = [](const SymbolRef &Symbol) {
+ Expected<uint32_t> SymFlagsOrErr = Symbol.getFlags();
+ if (!SymFlagsOrErr)
+ return false;
+ return (*SymFlagsOrErr & SymbolRef::SF_Undefined) &&
+ (*SymFlagsOrErr & SymbolRef::SF_Weak);
+ };
+
const bool IsAArch64 = BC->isAArch64();
const size_t RelSize = Relocation::getSizeForType(RType);
@@ -2098,7 +2106,8 @@ bool RewriteInstance::analyzeRelocation(
// Section symbols are marked as ST_Debug.
IsSectionRelocation = (cantFail(Symbol.getType()) == SymbolRef::ST_Debug);
// Check for PLT entry registered with symbol name
- if (!SymbolAddress && (IsAArch64 || BC->isRISCV())) {
+ if (!SymbolAddress && !IsWeakReference(Symbol) &&
+ (IsAArch64 || BC->isRISCV())) {
const BinaryData *BD = BC->getPLTBinaryDataByName(SymbolName);
SymbolAddress = BD ? BD->getAddress() : 0;
}
diff --git a/bolt/test/AArch64/update-weak-reference-symbol.s b/bolt/test/AArch64/update-weak-reference-symbol.s
new file mode 100644
index 0000000000000..6de4ce5dfdccf
--- /dev/null
+++ b/bolt/test/AArch64/update-weak-reference-symbol.s
@@ -0,0 +1,77 @@
+// This test checks whether BOLT can correctly handle relocations against weak symbols.
+
+// RUN: %clang %cflags -Wl,-z,notext -shared -Wl,-q %s -o %t.so
+// RUN: llvm-bolt %t.so -o %t.so.bolt
+
+// RUN: llvm-nm -n %t.so.bolt > %t.out.txt
+// RUN: llvm-objdump -dj .rodata %t.so.bolt >> %t.out.txt
+// RUN: FileCheck %s --input-file=%t.out.txt
+
+# CHECK: w func_1
+# CHECK: {{0+}}[[#%x,ADDR:]] W func_2
+
+# CHECK: {{.*}} <.rodata>:
+# CHECK-NEXT: {{.*}} .word 0x00000000
+# CHECK-NEXT: {{.*}} .word 0x00000000
+# CHECK-NEXT: {{.*}} .word 0x{{[0]+}}[[#ADDR]]
+# CHECK-NEXT: {{.*}} .word 0x00000000
+
+ .arch armv8-a
+ .text
+ .align 2
+ .global wow
+ .type wow, %function
+wow:
+.LFB0:
+ .cfi_startproc
+ stp x29, x30, [sp, -16]!
+ .cfi_def_cfa_offset 16
+ .cfi_offset 29, -16
+ .cfi_offset 30, -8
+ mov x29, sp
+ adrp x0, .LC0
+ add x0, x0, :lo12:.LC0
+ ldr x0, [x0]
+ cmp x0, 0
+ beq .L2
+ bl func_1
+.L2:
+ adrp x0, .LC1
+ add x0, x0, :lo12:.LC1
+ ldr x0, [x0]
+ cmp x0, 0
+ beq .L5
+ bl func_2
+ nop
+.L5:
+ nop
+ ldp x29, x30, [sp], 16
+ .cfi_restore 30
+ .cfi_restore 29
+ .cfi_def_cfa_offset 0
+ ret
+ .cfi_endproc
+.LFE0:
+ .size wow, .-wow
+ .section .rodata
+ .align 3
+.LC0:
+ .xword func_1
+ .align 3
+.LC1:
+ .xword func_2
+ .weak func_2
+ .weak func_1
+ .text
+ .align 2
+ .weak func_2
+ .type func_2, %function
+func_2:
+.LFB1:
+ .cfi_startproc
+ nop
+ ret
+ .cfi_endproc
+.LFE1:
+ .size func_2, .-func_2
+ .section .note.GNU-stack,"", at progbits
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