[lld] [lld][WebAssembly] Allow linker-synthetic symbols to be undefine when… (PR #153537)
YAMAMOTO Takashi via llvm-commits
llvm-commits at lists.llvm.org
Wed Aug 13 23:04:42 PDT 2025
https://github.com/yamt updated https://github.com/llvm/llvm-project/pull/153537
>From 7101db1acfea0adb879484b46ce4d275eff0789b Mon Sep 17 00:00:00 2001
From: Sam Clegg <sbc at chromium.org>
Date: Thu, 20 Feb 2025 17:11:20 -0800
Subject: [PATCH] [lld][WebAssembly] Allow linker-synthetic symbols to be
undefine when building shared libraries
Fixes: #103592
Co-authored-by: YAMAMOTO Takashi <yamamoto at midokura.com>
---
lld/test/wasm/shared-synthetic-symbols.s | 75 ++++++++++++++++++++++++
lld/wasm/Driver.cpp | 36 ++++++++----
2 files changed, 99 insertions(+), 12 deletions(-)
create mode 100644 lld/test/wasm/shared-synthetic-symbols.s
diff --git a/lld/test/wasm/shared-synthetic-symbols.s b/lld/test/wasm/shared-synthetic-symbols.s
new file mode 100644
index 0000000000000..0c9c68aabc239
--- /dev/null
+++ b/lld/test/wasm/shared-synthetic-symbols.s
@@ -0,0 +1,75 @@
+## Check that synthetic data-layout symbols such as __heap_base and __heap_end
+## can be referenced from shared libraries and pie executables without
+## generating undefined symbols.
+
+# RUN: llvm-mc -filetype=obj -triple=wasm32-unknown-unknown -o %t.o %s
+# RUN: wasm-ld --experimental-pic -pie --import-memory -o %t.wasm %t.o
+# RUN: obj2yaml %t.wasm | FileCheck %s
+# RUN: wasm-ld --experimental-pic -shared -o %t.so %t.o
+# RUN: obj2yaml %t.so | FileCheck %s
+
+.globl _start
+
+_start:
+ .functype _start () -> ()
+ i32.const __heap_base at GOT
+ drop
+ i32.const __heap_end at GOT
+ drop
+ i32.const __stack_low at GOT
+ drop
+ i32.const __stack_high at GOT
+ drop
+ i32.const __global_base at GOT
+ drop
+ i32.const __data_end at GOT
+ drop
+ end_function
+
+# CHECK: - Type: IMPORT
+# CHECK-NEXT: Imports:
+# CHECK-NEXT: - Module: env
+# CHECK-NEXT: Field: memory
+# CHECK-NEXT: Kind: MEMORY
+# CHECK-NEXT: Memory:
+# CHECK-NEXT: Minimum: 0x0
+# CHECK-NEXT: - Module: env
+# CHECK-NEXT: Field: __memory_base
+# CHECK-NEXT: Kind: GLOBAL
+# CHECK-NEXT: GlobalType: I32
+# CHECK-NEXT: GlobalMutable: false
+# CHECK-NEXT: - Module: env
+# CHECK-NEXT: Field: __table_base
+# CHECK-NEXT: Kind: GLOBAL
+# CHECK-NEXT: GlobalType: I32
+# CHECK-NEXT: GlobalMutable: false
+# CHECK-NEXT: - Module: GOT.mem
+# CHECK-NEXT: Field: __heap_base
+# CHECK-NEXT: Kind: GLOBAL
+# CHECK-NEXT: GlobalType: I32
+# CHECK-NEXT: GlobalMutable: true
+# CHECK-NEXT: - Module: GOT.mem
+# CHECK-NEXT: Field: __heap_end
+# CHECK-NEXT: Kind: GLOBAL
+# CHECK-NEXT: GlobalType: I32
+# CHECK-NEXT: GlobalMutable: true
+# CHECK-NEXT: - Module: GOT.mem
+# CHECK-NEXT: Field: __stack_low
+# CHECK-NEXT: Kind: GLOBAL
+# CHECK-NEXT: GlobalType: I32
+# CHECK-NEXT: GlobalMutable: true
+# CHECK-NEXT: - Module: GOT.mem
+# CHECK-NEXT: Field: __stack_high
+# CHECK-NEXT: Kind: GLOBAL
+# CHECK-NEXT: GlobalType: I32
+# CHECK-NEXT: GlobalMutable: true
+# CHECK-NEXT: - Module: GOT.mem
+# CHECK-NEXT: Field: __global_base
+# CHECK-NEXT: Kind: GLOBAL
+# CHECK-NEXT: GlobalType: I32
+# CHECK-NEXT: GlobalMutable: true
+# CHECK-NEXT: - Module: GOT.mem
+# CHECK-NEXT: Field: __data_end
+# CHECK-NEXT: Kind: GLOBAL
+# CHECK-NEXT: GlobalType: I32
+# CHECK-NEXT: GlobalMutable: true
diff --git a/lld/wasm/Driver.cpp b/lld/wasm/Driver.cpp
index 1c5d21c06f5af..64ff9a95bb2d1 100644
--- a/lld/wasm/Driver.cpp
+++ b/lld/wasm/Driver.cpp
@@ -985,23 +985,35 @@ static void createOptionalSymbols() {
ctx.sym.dsoHandle = symtab->addOptionalDataSymbol("__dso_handle");
- if (!ctx.arg.shared)
- ctx.sym.dataEnd = symtab->addOptionalDataSymbol("__data_end");
-
+ auto addDataLayoutSymbol = [&](StringRef s) -> DefinedData * {
+ // Data layout symbols are either defined by lld, or (in the case
+ // of PIC code) defined by the dynamic linker / embedder.
+ if (ctx.isPic) {
+ ctx.arg.allowUndefinedSymbols.insert(s);
+ return nullptr;
+ } else {
+ return symtab->addOptionalDataSymbol(s);
+ }
+ };
+
+ ctx.sym.dataEnd = addDataLayoutSymbol("__data_end");
+ ctx.sym.stackLow = addDataLayoutSymbol("__stack_low");
+ ctx.sym.stackHigh = addDataLayoutSymbol("__stack_high");
+ ctx.sym.globalBase = addDataLayoutSymbol("__global_base");
+ ctx.sym.heapBase = addDataLayoutSymbol("__heap_base");
+ ctx.sym.heapEnd = addDataLayoutSymbol("__heap_end");
+
+ // for pic,
+ // - __memory_base and __table_base are handled in createSyntheticSymbols.
+ // - how __wasm_first_page_end should be is not clear yet.
if (!ctx.isPic) {
- ctx.sym.stackLow = symtab->addOptionalDataSymbol("__stack_low");
- ctx.sym.stackHigh = symtab->addOptionalDataSymbol("__stack_high");
- ctx.sym.globalBase = symtab->addOptionalDataSymbol("__global_base");
- ctx.sym.heapBase = symtab->addOptionalDataSymbol("__heap_base");
- ctx.sym.heapEnd = symtab->addOptionalDataSymbol("__heap_end");
ctx.sym.definedMemoryBase = symtab->addOptionalDataSymbol("__memory_base");
ctx.sym.definedTableBase = symtab->addOptionalDataSymbol("__table_base");
+ ctx.sym.firstPageEnd = symtab->addOptionalDataSymbol("__wasm_first_page_end");
+ if (ctx.sym.firstPageEnd)
+ ctx.sym.firstPageEnd->setVA(ctx.arg.pageSize);
}
- ctx.sym.firstPageEnd = symtab->addOptionalDataSymbol("__wasm_first_page_end");
- if (ctx.sym.firstPageEnd)
- ctx.sym.firstPageEnd->setVA(ctx.arg.pageSize);
-
// 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
// programs, and such object files can contain references to this symbol.
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