[lld] Reapply "[lld][WebAssembly] Do not relocate ABSOLUTE symbols" (#154371) (PR #154494)
YAMAMOTO Takashi via llvm-commits
llvm-commits at lists.llvm.org
Wed Aug 20 02:21:44 PDT 2025
https://github.com/yamt created https://github.com/llvm/llvm-project/pull/154494
This reverts commit 28f2fb24e1668943172cfd7a381c4262d51615b4.
The previous attempt was breaking things like __start_ symbols.
This time, use a separate flag instead of abusing ABOSULUTE.
>From 576af7e810dbde174308ebdd6bc5484a98a53575 Mon Sep 17 00:00:00 2001
From: YAMAMOTO Takashi <yamamoto at midokura.com>
Date: Wed, 20 Aug 2025 17:57:48 +0900
Subject: [PATCH] Reapply "[lld][WebAssembly] Do not relocate ABSOLUTE symbols"
(#154371)
This reverts commit 28f2fb24e1668943172cfd7a381c4262d51615b4.
The previous attempt was breaking things like __start_ symbols.
This time, use a separate flag instead of abusing ABOSULUTE.
---
lld/test/wasm/pie.s | 27 ++++++++++++++++++++++++---
lld/wasm/Driver.cpp | 4 +++-
lld/wasm/Symbols.h | 5 ++++-
lld/wasm/SyntheticSections.cpp | 4 +++-
4 files changed, 34 insertions(+), 6 deletions(-)
diff --git a/lld/test/wasm/pie.s b/lld/test/wasm/pie.s
index 21eac79207318..78d6c85097b10 100644
--- a/lld/test/wasm/pie.s
+++ b/lld/test/wasm/pie.s
@@ -2,7 +2,7 @@
# RUN: llvm-mc -filetype=obj -triple=wasm32-unknown-emscripten %S/Inputs/internal_func.s -o %t.internal_func.o
# RUN: wasm-ld --no-gc-sections --experimental-pic -pie --unresolved-symbols=import-dynamic -o %t.wasm %t.o %t.internal_func.o
# RUN: obj2yaml %t.wasm | FileCheck %s
-# RUN: llvm-objdump --disassemble-symbols=__wasm_call_ctors,__wasm_apply_data_relocs --no-show-raw-insn --no-leading-addr %t.wasm | FileCheck %s --check-prefixes DISASSEM
+# RUN: llvm-objdump --disassemble-symbols=__wasm_call_ctors,__wasm_apply_data_relocs,__wasm_apply_global_relocs --no-show-raw-insn --no-leading-addr %t.wasm | FileCheck %s --check-prefixes DISASSEM
.functype external_func () -> ()
.functype internal_func1 () -> (i32)
@@ -41,6 +41,9 @@ foo:
drop
global.get __stack_pointer
+ drop
+
+ global.get __wasm_first_page_end at GOT
end_function
get_data_address:
@@ -145,6 +148,18 @@ _start:
# DISASSEM-LABEL: <__wasm_apply_data_relocs>:
# DISASSEM: end
+# global 6 is __wasm_first_page_end, which is noReloc and
+# thus should not be relocated.
+#
+# DISASSEM-LABEL: <__wasm_apply_global_relocs>:
+# DISASSEM: global.set 4
+# DISASSEM: global.set 5
+# DISASSEM-NOT: global.set 6
+# DISASSEM: global.set 7
+# DISASSEM: global.set 8
+# DISASSEM: global.set 9
+# DISASSEM: end
+
# Run the same test with extended-const support. When this is available
# we don't need __wasm_apply_global_relocs and instead rely on the add
# instruction in the InitExpr. We also, therefore, do not need these globals
@@ -173,17 +188,23 @@ _start:
# EXTENDED-CONST-NEXT: Type: I32
# EXTENDED-CONST-NEXT: Mutable: false
# EXTENDED-CONST-NEXT: InitExpr:
+# EXTENDED-CONST-NEXT: Opcode: I32_CONST
+# EXTENDED-CONST-NEXT: Value: 65536
+# EXTENDED-CONST-NEXT: - Index: 7
+# EXTENDED-CONST-NEXT: Type: I32
+# EXTENDED-CONST-NEXT: Mutable: false
+# EXTENDED-CONST-NEXT: InitExpr:
# EXTENDED-CONST-NEXT: Extended: true
# This instruction sequence decodes to:
# (global.get[0x23] 0x1 i32.const[0x41] 0x0C i32.add[0x6A] end[0x0b])
# EXTENDED-CONST-NEXT: Body: 2301410C6A0B
-# EXTENDED-CONST-NEXT: - Index: 7
+# EXTENDED-CONST-NEXT: - Index: 8
# EXTENDED-CONST-NEXT: Type: I32
# EXTENDED-CONST-NEXT: Mutable: false
# EXTENDED-CONST-NEXT: InitExpr:
# EXTENDED-CONST-NEXT: Opcode: GLOBAL_GET
# EXTENDED-CONST-NEXT: Index: 2
-# EXTENDED-CONST-NEXT: - Index: 8
+# EXTENDED-CONST-NEXT: - Index: 9
# EXTENDED-CONST-NEXT: Type: I32
# EXTENDED-CONST-NEXT: Mutable: false
# EXTENDED-CONST-NEXT: InitExpr:
diff --git a/lld/wasm/Driver.cpp b/lld/wasm/Driver.cpp
index 1c5d21c06f5af..5ad8c1bde289d 100644
--- a/lld/wasm/Driver.cpp
+++ b/lld/wasm/Driver.cpp
@@ -999,8 +999,10 @@ static void createOptionalSymbols() {
}
ctx.sym.firstPageEnd = symtab->addOptionalDataSymbol("__wasm_first_page_end");
- if (ctx.sym.firstPageEnd)
+ if (ctx.sym.firstPageEnd) {
ctx.sym.firstPageEnd->setVA(ctx.arg.pageSize);
+ ctx.sym.firstPageEnd->noReloc = true;
+ }
// For non-shared memory programs we still need to define __tls_base since we
// allow object files built with TLS to be linked into single threaded
diff --git a/lld/wasm/Symbols.h b/lld/wasm/Symbols.h
index 55ee21939ce07..caee04865545d 100644
--- a/lld/wasm/Symbols.h
+++ b/lld/wasm/Symbols.h
@@ -142,7 +142,7 @@ class Symbol {
: name(name), file(f), symbolKind(k), referenced(!ctx.arg.gcSections),
requiresGOT(false), isUsedInRegularObj(false), forceExport(false),
forceImport(false), canInline(false), traced(false), isStub(false),
- flags(flags) {}
+ noReloc(false), flags(flags) {}
StringRef name;
InputFile *file;
@@ -185,6 +185,9 @@ class Symbol {
// the null function pointer).
bool isStub : 1;
+ // True if this symbol is not relative to __memory_base.
+ bool noReloc : 1;
+
uint32_t flags;
std::optional<StringRef> importName;
diff --git a/lld/wasm/SyntheticSections.cpp b/lld/wasm/SyntheticSections.cpp
index e1192706ea913..4d0c5abf799db 100644
--- a/lld/wasm/SyntheticSections.cpp
+++ b/lld/wasm/SyntheticSections.cpp
@@ -440,6 +440,8 @@ void GlobalSection::generateRelocationCode(raw_ostream &os, bool TLS) const {
: WASM_OPCODE_I32_ADD;
for (const Symbol *sym : internalGotSymbols) {
+ if (sym->noReloc)
+ continue;
if (TLS != sym->isTLS())
continue;
@@ -503,7 +505,7 @@ void GlobalSection::writeBody() {
bool useExtendedConst = false;
uint32_t globalIdx;
int64_t offset;
- if (ctx.arg.extendedConst && ctx.isPic) {
+ if (ctx.arg.extendedConst && ctx.isPic && !sym->noReloc) {
if (auto *d = dyn_cast<DefinedData>(sym)) {
if (!sym->isTLS()) {
globalIdx = ctx.sym.memoryBase->getGlobalIndex();
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