[lld] [lld][WebAssembly] Honor requiredInBinary when combining data segments (PR #127735)
Sam Clegg via llvm-commits
llvm-commits at lists.llvm.org
Tue Feb 18 17:59:35 PST 2025
https://github.com/sbc100 created https://github.com/llvm/llvm-project/pull/127735
In most circumstances BSS segments are not required in the output binary but combineOutputSegments was erroneously including them. This meant that PIC binaries were including the BSS data as zero in the binary.
Fixes: https://github.com/emscripten-core/emscripten/issues/23683
>From d0f2c6feedf88b3dfe8ce89839f99c386fff6397 Mon Sep 17 00:00:00 2001
From: Sam Clegg <sbc at chromium.org>
Date: Tue, 18 Feb 2025 14:07:04 -0800
Subject: [PATCH] [lld][WebAssembly] Honor requiredInBinary when combining data
segments
In most circumstances BSS segments are not required in the output binary
but combineOutputSegments was erroneously including them. This meant
that PIC binaries were including the BSS data as zero in the binary.
Fixes: https://github.com/emscripten-core/emscripten/issues/23683
---
lld/test/wasm/data-segments.ll | 39 ++++++++++++++++++++++++++++++----
lld/wasm/OutputSections.cpp | 3 ++-
lld/wasm/Writer.cpp | 7 +++++-
3 files changed, 43 insertions(+), 6 deletions(-)
diff --git a/lld/test/wasm/data-segments.ll b/lld/test/wasm/data-segments.ll
index 79f1d384919d9..e36f0a7a95332 100644
--- a/lld/test/wasm/data-segments.ll
+++ b/lld/test/wasm/data-segments.ll
@@ -17,6 +17,11 @@
; RUN: wasm-ld -mwasm64 -no-gc-sections --no-entry %t.bulk-mem64.o -o %t.bulk-mem64.wasm
; RUN: obj2yaml %t.bulk-mem64.wasm | FileCheck %s --check-prefixes ACTIVE,ACTIVE64
+;; In -pie mode segments are combined into one active segment.
+; RUN: wasm-ld --experimental-pic --import-memory -pie -no-gc-sections --no-entry %t.atomics.bulk-mem.pic.o -o %t.pic.wasm
+; RUN: obj2yaml %t.pic.wasm | FileCheck %s --check-prefixes ACTIVE-PIC
+; RUN: llvm-objdump --disassemble-symbols=__wasm_call_ctors,__wasm_init_memory --no-show-raw-insn --no-leading-addr %t.pic.wasm | FileCheck %s --check-prefixes PIC-NON-SHARED-DIS
+
;; atomics, bulk memory, shared memory => passive segments
; RUN: wasm-ld -no-gc-sections --no-entry --shared-memory --max-memory=131072 %t.atomics.bulk-mem.o -o %t.atomics.bulk-mem.wasm
; RUN: obj2yaml %t.atomics.bulk-mem.wasm | FileCheck %s --check-prefix PASSIVE
@@ -28,9 +33,9 @@
; RUN: llvm-objdump --disassemble-symbols=__wasm_call_ctors,__wasm_init_memory --no-show-raw-insn --no-leading-addr %t.atomics.bulk-mem64.wasm | FileCheck %s --check-prefixes DIS,NOPIC-DIS -DPTR=i64
;; Also test in combination with PIC/pie
-; RUN: wasm-ld --experimental-pic -pie -no-gc-sections --no-entry --shared-memory --max-memory=131072 %t.atomics.bulk-mem.pic.o -o %t.pic.wasm
-; RUN: obj2yaml %t.pic.wasm | FileCheck %s --check-prefixes PASSIVE-PIC,PASSIVE32-PIC
-; RUN: llvm-objdump --disassemble-symbols=__wasm_call_ctors,__wasm_init_memory --no-show-raw-insn --no-leading-addr %t.pic.wasm | FileCheck %s --check-prefixes DIS,PIC-DIS -DPTR=i32
+; RUN: wasm-ld --experimental-pic -pie -no-gc-sections --no-entry --shared-memory --max-memory=131072 %t.atomics.bulk-mem.pic.o -o %t.shared.pic.wasm
+; RUN: obj2yaml %t.shared.pic.wasm | FileCheck %s --check-prefixes PASSIVE-PIC,PASSIVE32-PIC
+; RUN: llvm-objdump --disassemble-symbols=__wasm_call_ctors,__wasm_init_memory --no-show-raw-insn --no-leading-addr %t.shared.pic.wasm | FileCheck %s --check-prefixes DIS,PIC-DIS -DPTR=i32
;; Also test in combination with PIC/pie + wasm64
; RUN: wasm-ld -mwasm64 --experimental-pic -pie -no-gc-sections --no-entry --shared-memory --max-memory=131072 %t.atomics.bulk-mem.pic-mem64.o -o %t.pic-mem64.wasm
@@ -47,7 +52,7 @@
@g = thread_local global i32 99, align 4
-; ERROR: 'bulk-memory' feature must be used in order to use shared memory
+;; ERROR: 'bulk-memory' feature must be used in order to use shared memory
; ACTIVE-LABEL: - Type: CODE
; ACTIVE-NEXT: Functions:
@@ -76,6 +81,20 @@
; ACTIVE-NEXT: - Index: 0
; ACTIVE-NEXT: Name: __wasm_call_ctors
+;; In ACTIVE-PIC mode the memory is imported which means all data segments
+;; (except BSS) are combined in the single one.
+;; BSS is not included here, and instead initialized using `memory.init` in
+;; `__wasm_init_memory`
+
+; ACTIVE-PIC: - Type: DATA
+; ACTIVE-PIC-NEXT: Segments:
+; ACTIVE-PIC-NEXT: - SectionOffset: 6
+; ACTIVE-PIC-NEXT: InitFlags: 0
+; ACTIVE-PIC-NEXT: Offset:
+; ACTIVE-PIC-NEXT: Opcode: GLOBAL_GET
+; ACTIVE-PIC-NEXT: Index: 1
+; ACTIVE-PIC-NEXT: Content: 63000000636F6E7374616E74000000002B00000068656C6C6F00676F6F646279650000002A000000
+
; PASSIVE-LABEL: - Type: START
; PASSIVE-NEXT: StartFunction: 2
; PASSIVE-LABEL: - Type: DATACOUNT
@@ -151,6 +170,18 @@
; PASSIVE-PIC-NEXT: - Index: 2
; PASSIVE-PIC-NEXT: Name: __wasm_init_memory
+;; For the non-shared PIC case the __wasm_init_memory only deals with BSS since
+;; all other segments are active
+; PIC-NON-SHARED-DIS: <__wasm_init_memory>:
+; PIC-NON-SHARED-DIS-EMPTY:
+; PIC-NON-SHARED-DIS-NEXT: i32.const 40
+; PIC-NON-SHARED-DIS-NEXT: global.get 1
+; PIC-NON-SHARED-DIS-NEXT: i32.add
+; PIC-NON-SHARED-DIS-NEXT: i32.const 0
+; PIC-NON-SHARED-DIS-NEXT: i32.const 10000
+; PIC-NON-SHARED-DIS-NEXT: memory.fill 0
+; PIC-NON-SHARED-DIS-NEXT: end
+
;; no data relocations.
; DIS-LABEL: <__wasm_call_ctors>:
; DIS-EMPTY:
diff --git a/lld/wasm/OutputSections.cpp b/lld/wasm/OutputSections.cpp
index 95f7ecc29de6b..d679d1e676479 100644
--- a/lld/wasm/OutputSections.cpp
+++ b/lld/wasm/OutputSections.cpp
@@ -101,7 +101,8 @@ void DataSection::finalizeContents() {
});
#ifndef NDEBUG
unsigned activeCount = llvm::count_if(segments, [](OutputSegment *segment) {
- return (segment->initFlags & WASM_DATA_SEGMENT_IS_PASSIVE) == 0;
+ return segment->requiredInBinary() &&
+ (segment->initFlags & WASM_DATA_SEGMENT_IS_PASSIVE) == 0;
});
#endif
diff --git a/lld/wasm/Writer.cpp b/lld/wasm/Writer.cpp
index 76e38f548157c..7770bdcfc1f16 100644
--- a/lld/wasm/Writer.cpp
+++ b/lld/wasm/Writer.cpp
@@ -1081,7 +1081,12 @@ void Writer::combineOutputSegments() {
return;
OutputSegment *combined = make<OutputSegment>(".data");
combined->startVA = segments[0]->startVA;
+ std::vector<OutputSegment *> newSegments = {combined};
for (OutputSegment *s : segments) {
+ if (!s->requiredInBinary()) {
+ newSegments.push_back(s);
+ continue;
+ }
bool first = true;
for (InputChunk *inSeg : s->inputSegments) {
if (first)
@@ -1100,7 +1105,7 @@ void Writer::combineOutputSegments() {
}
}
- segments = {combined};
+ segments = newSegments;
}
static void createFunction(DefinedFunction *func, StringRef bodyContent) {
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