release/19.x: [BOLT] Skip PLT search for zero-value weak reference symbols (#69136)#102295
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tru merged 1 commit intollvm:release/19.xfrom Aug 10, 2024
Merged
release/19.x: [BOLT] Skip PLT search for zero-value weak reference symbols (#69136)#102295tru merged 1 commit intollvm:release/19.xfrom
tru merged 1 commit intollvm:release/19.xfrom
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@yota9 What do you think about merging this PR to the release branch? |
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@llvm/pr-subscribers-bolt Author: None (llvmbot) ChangesBackport 6c8933e Requested by: @linsinan1995 Full diff: https://github.com/llvm/llvm-project/pull/102295.diff 2 Files Affected:
diff --git a/bolt/lib/Rewrite/RewriteInstance.cpp b/bolt/lib/Rewrite/RewriteInstance.cpp
index 33ebae3b6e6de2..45d594ef3fa6f5 100644
--- a/bolt/lib/Rewrite/RewriteInstance.cpp
+++ b/bolt/lib/Rewrite/RewriteInstance.cpp
@@ -2143,6 +2143,14 @@ 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);
@@ -2174,7 +2182,8 @@ 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 00000000000000..600a06b8b6d8fd
--- /dev/null
+++ b/bolt/test/AArch64/update-weak-reference-symbol.s
@@ -0,0 +1,34 @@
+// 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
+
+ .text
+ .weak func_2
+ .weak func_1
+ .global wow
+ .type wow, %function
+wow:
+ bl func_1
+ bl func_2
+ ret
+ .type func_2, %function
+func_2:
+ ret
+ .section .rodata
+.LC0:
+ .xword func_1
+.LC1:
+ .xword func_2
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) 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@PLT, leading to incorrect runtime behavior. (cherry picked from commit 6c8933e)
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@linsinan1995 (or anyone else). If you would like to add a note about this fix in the release notes (completely optional). Please reply to this comment with a one or two sentence description of the fix. When you are done, please add the release:note label to this PR. |
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Backport 6c8933e
Requested by: @linsinan1995