97 lines
3.1 KiB
Diff
97 lines
3.1 KiB
Diff
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From 6c8933e1a095028d648a5a26aecee0f569304dd0 Mon Sep 17 00:00:00 2001
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From: sinan <sinan.lin@linux.alibaba.com>
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Date: Wed, 7 Aug 2024 18:02:42 +0800
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Subject: [PATCH] [BOLT] Skip PLT search for zero-value weak reference symbols
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(#69136)
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Take a common weak reference pattern for example
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```
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__attribute__((weak)) void undef_weak_fun();
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if (&undef_weak_fun)
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undef_weak_fun();
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```
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In this case, an undefined weak symbol `undef_weak_fun` has an address
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of zero, and Bolt incorrectly changes the relocation for the
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corresponding symbol to symbol@PLT, leading to incorrect runtime
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behavior.
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---
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bolt/lib/Rewrite/RewriteInstance.cpp | 11 +++++-
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.../AArch64/update-weak-reference-symbol.s | 34 +++++++++++++++++++
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2 files changed, 44 insertions(+), 1 deletion(-)
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create mode 100644 bolt/test/AArch64/update-weak-reference-symbol.s
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diff --git a/bolt/lib/Rewrite/RewriteInstance.cpp b/bolt/lib/Rewrite/RewriteInstance.cpp
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index 78b4889bf2ae..d2e2ca2f7553 100644
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--- a/bolt/lib/Rewrite/RewriteInstance.cpp
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+++ b/bolt/lib/Rewrite/RewriteInstance.cpp
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@@ -2143,6 +2143,14 @@ bool RewriteInstance::analyzeRelocation(
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if (!Relocation::isSupported(RType))
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return false;
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+ auto IsWeakReference = [](const SymbolRef &Symbol) {
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+ Expected<uint32_t> SymFlagsOrErr = Symbol.getFlags();
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+ if (!SymFlagsOrErr)
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+ return false;
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+ return (*SymFlagsOrErr & SymbolRef::SF_Undefined) &&
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+ (*SymFlagsOrErr & SymbolRef::SF_Weak);
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+ };
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+
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const bool IsAArch64 = BC->isAArch64();
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const size_t RelSize = Relocation::getSizeForType(RType);
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@@ -2174,7 +2182,8 @@ bool RewriteInstance::analyzeRelocation(
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// Section symbols are marked as ST_Debug.
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IsSectionRelocation = (cantFail(Symbol.getType()) == SymbolRef::ST_Debug);
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// Check for PLT entry registered with symbol name
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- if (!SymbolAddress && (IsAArch64 || BC->isRISCV())) {
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+ if (!SymbolAddress && !IsWeakReference(Symbol) &&
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+ (IsAArch64 || BC->isRISCV())) {
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const BinaryData *BD = BC->getPLTBinaryDataByName(SymbolName);
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SymbolAddress = BD ? BD->getAddress() : 0;
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}
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diff --git a/bolt/test/AArch64/update-weak-reference-symbol.s b/bolt/test/AArch64/update-weak-reference-symbol.s
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new file mode 100644
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index 000000000000..600a06b8b6d8
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--- /dev/null
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+++ b/bolt/test/AArch64/update-weak-reference-symbol.s
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@@ -0,0 +1,34 @@
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+// This test checks whether BOLT can correctly handle relocations against weak symbols.
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+
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+// RUN: %clang %cflags -Wl,-z,notext -shared -Wl,-q %s -o %t.so
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+// RUN: llvm-bolt %t.so -o %t.so.bolt
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+// RUN: llvm-nm -n %t.so.bolt > %t.out.txt
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+// RUN: llvm-objdump -dj .rodata %t.so.bolt >> %t.out.txt
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+// RUN: FileCheck %s --input-file=%t.out.txt
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+
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+# CHECK: w func_1
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+# CHECK: {{0+}}[[#%x,ADDR:]] W func_2
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+
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+# CHECK: {{.*}} <.rodata>:
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+# CHECK-NEXT: {{.*}} .word 0x00000000
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+# CHECK-NEXT: {{.*}} .word 0x00000000
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+# CHECK-NEXT: {{.*}} .word 0x{{[0]+}}[[#ADDR]]
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+# CHECK-NEXT: {{.*}} .word 0x00000000
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+
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+ .text
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+ .weak func_2
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+ .weak func_1
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+ .global wow
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+ .type wow, %function
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+wow:
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+ bl func_1
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+ bl func_2
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+ ret
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+ .type func_2, %function
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+func_2:
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+ ret
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+ .section .rodata
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+.LC0:
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+ .xword func_1
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+.LC1:
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+ .xword func_2
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--
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2.39.3 (Apple Git-146)
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