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[lld][WebAssembly] Generate TLS relocation code also when linking statically

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Previously relocations were only generated for PIC output, but
relocations for TLS GOT entries are always needed when shared
memory is enabled, not just in PIC mode.

This means that the `__wasm_apply_global_tls_relocs` is now
generated even for statically linked (non-PIC) output.  Without
this the globals that hold the addresses of TLS symbols are
not set correctly.

Differential Revision: https://reviews.llvm.org/D112833
This commit is contained in:
Sam Clegg 2021-10-29 09:58:56 -07:00
parent fe953b15cf
commit 182b72aa48
6 changed files with 67 additions and 25 deletions
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10
lld/test/wasm/pie.ll
View File

@ -91,7 +91,7 @@ declare void @external_func()
; RUN: obj2yaml %t.shmem.wasm | FileCheck %s --check-prefix=SHMEM
; SHMEM: - Type: CODE
; SHMEM: - Index: 7
; SHMEM: - Index: 6
; SHMEM-NEXT: Locals: []
; SHMEM-NEXT: Body: 100310050B
@ -109,13 +109,11 @@ declare void @external_func()
; SHMEM-NEXT: - Index: 5
; SHMEM-NEXT: Name: __wasm_apply_global_relocs
; SHMEM-NEXT: - Index: 6
; SHMEM-NEXT: Name: __wasm_apply_global_tls_relocs
; SHMEM-NEXT: - Index: 7
; SHMEM-NEXT: Name: __wasm_start
; SHMEM-NEXT: - Index: 8
; SHMEM-NEXT: - Index: 7
; SHMEM-NEXT: Name: foo
; SHMEM-NEXT: - Index: 9
; SHMEM-NEXT: - Index: 8
; SHMEM-NEXT: Name: get_data_address
; SHMEM-NEXT: - Index: 10
; SHMEM-NEXT: - Index: 9
; SHMEM-NEXT: Name: _start

3
lld/test/wasm/tls-non-shared-memory.s
View File

@ -48,6 +48,9 @@ tls1:
# RUN: wasm-ld --experimental-pic -shared -o %t.so %t.o
# RUN: obj2yaml %t.so | FileCheck %s --check-prefix=PIC
# RUN: wasm-ld --experimental-pic --no-gc-sections --no-entry -pie -o %t-pie.wasm %t.o
# RUN: obj2yaml %t.so | FileCheck %s --check-prefix=PIC
# CHECK: - Type: GLOBAL
# __stack_pointer
# CHECK-NEXT: Globals:

37
lld/test/wasm/tls.s
View File

@ -33,6 +33,17 @@ tls_align:
global.get __tls_align
end_function
# TLS symbols can also be accessed by `global.get tls1@GOT@TLS`
# which is the pattern emitted for non-DSO-local symbols.
# In this case the global that holds that address must be
# initialized by `__wasm_apply_global_tls_relocs` which is
# called by `__wasm_init_tls`.
.globl tls1_got_addr
tls1_got_addr:
.functype tls1_got_addr () -> (i32)
global.get tls1@GOT@TLS
end_function
.section .bss.no_tls,"",@
.globl no_tls
.p2align 2
@ -114,7 +125,7 @@ tls3:
# CHECK-NEXT: Value: 4
# ASM: <__wasm_init_tls>:
# ASM-LABEL: <__wasm_init_tls>:
# ASM-EMPTY:
# ASM-NEXT: local.get 0
# ASM-NEXT: global.set 1
@ -122,33 +133,43 @@ tls3:
# ASM-NEXT: i32.const 0
# ASM-NEXT: i32.const 12
# ASM-NEXT: memory.init 0, 0
# call to __wasm_apply_global_tls_relocs>
# ASM-NEXT: call 3
# ASM-NEXT: end
# ASM: <tls1_addr>:
# ASM-LABEL: <__wasm_apply_global_tls_relocs>:
# ASM-EMPTY:
# ASM-NEXT: global.get 1
# ASM-NEXT: i32.const 0
# ASM-NEXT: i32.add
# ASM-NEXT: global.set 4
# ASM-NEXT: end
# ASM-LABEL: <tls1_addr>:
# ASM-EMPTY:
# ASM-NEXT: global.get 1
# ASM-NEXT: i32.const 0
# ASM-NEXT: i32.add
# ASM-NEXT: end
# ASM: <tls2_addr>:
# ASM-LABEL: <tls2_addr>:
# ASM-EMPTY:
# ASM-NEXT: global.get 1
# ASM-NEXT: i32.const 4
# ASM-NEXT: i32.add
# ASM-NEXT: end
# ASM: <tls3_addr>:
# ASM-LABEL: <tls3_addr>:
# ASM-EMPTY:
# ASM-NEXT: global.get 1
# ASM-NEXT: i32.const 8
# ASM-NEXT: i32.add
# ASM-NEXT: end
# ASM: <tls_align>:
# ASM-LABEL: <tls_align>:
# ASM-EMPTY:
# ASM-NEXT: global.get 3
# ASM-NEXT: end
# ASM-NEXT: global.get 3
# ASM-NEXT: end
# Also verify TLS usage with --relocatable
# RUN: wasm-ld --relocatable -o %t3.wasm %t.o
@ -172,6 +193,8 @@ tls3:
# RELOC-NEXT: Name: __tls_base
# RELOC-NEXT: - Index: 1
# RELOC-NEXT: Name: __tls_align
# RELOC-NEXT: - Index: 2
# RELOC-NEXT: Name: GOT.data.internal.tls1
# RELOC-NEXT: DataSegmentNames:
# RELOC-NEXT: - Index: 0
# RELOC-NEXT: Name: .tdata

16
lld/wasm/SyntheticSections.cpp
View File

@ -455,10 +455,18 @@ void GlobalSection::writeBody() {
bool is64 = config->is64.getValueOr(false);
uint8_t itype = is64 ? WASM_TYPE_I64 : WASM_TYPE_I32;
for (const Symbol *sym : internalGotSymbols) {
// In the case of dynamic linking, internal GOT entries
// need to be mutable since they get updated to the correct
// runtime value during `__wasm_apply_global_relocs`.
bool mutable_ = config->isPic & !sym->isStub;
bool mutable_ = false;
if (!sym->isStub) {
// In the case of dynamic linking, these global must to be mutable since
// they get updated to the correct runtime value during
// `__wasm_apply_global_relocs`.
if (config->isPic && !sym->isTLS())
mutable_ = true;
// With multi-theadeding any TLS globals must be mutable since they get
// set during `__wasm_apply_global_tls_relocs`
if (config->sharedMemory && sym->isTLS())
mutable_ = true;
}
WasmGlobalType type{itype, mutable_};
WasmInitExpr initExpr;
if (auto *d = dyn_cast<DefinedData>(sym))

11
lld/wasm/SyntheticSections.h
View File

@ -287,7 +287,16 @@ public:
// specific relocation types combined with linker relaxation which could
// transform a `global.get` to an `i32.const`.
void addInternalGOTEntry(Symbol *sym);
bool needsRelocations() { return internalGotSymbols.size(); }
bool needsRelocations() {
return llvm::find_if(internalGotSymbols, [=](Symbol *sym) {
return !sym->isTLS();
}) != internalGotSymbols.end();
}
bool needsTLSRelocations() {
return llvm::find_if(internalGotSymbols, [=](Symbol *sym) {
return sym->isTLS();
}) != internalGotSymbols.end();
}
void generateRelocationCode(raw_ostream &os, bool TLS) const;
std::vector<DefinedData *> dataAddressGlobals;

15
lld/wasm/Writer.cpp
View File

@ -997,6 +997,14 @@ void Writer::createSyntheticInitFunctions() {
WasmSym::initMemory->markLive();
}
if (config->sharedMemory && out.globalSec->needsTLSRelocations()) {
WasmSym::applyGlobalTLSRelocs = symtab->addSyntheticFunction(
"__wasm_apply_global_tls_relocs", WASM_SYMBOL_VISIBILITY_HIDDEN,
make<SyntheticFunction>(nullSignature,
"__wasm_apply_global_tls_relocs"));
WasmSym::applyGlobalTLSRelocs->markLive();
}
if (config->isPic) {
// For PIC code we create synthetic functions that apply relocations.
// These get called from __wasm_call_ctors before the user-level
@ -1011,13 +1019,6 @@ void Writer::createSyntheticInitFunctions() {
"__wasm_apply_global_relocs", WASM_SYMBOL_VISIBILITY_HIDDEN,
make<SyntheticFunction>(nullSignature, "__wasm_apply_global_relocs"));
WasmSym::applyGlobalRelocs->markLive();
if (config->sharedMemory) {
WasmSym::applyGlobalTLSRelocs = symtab->addSyntheticFunction(
"__wasm_apply_global_tls_relocs", WASM_SYMBOL_VISIBILITY_HIDDEN,
make<SyntheticFunction>(nullSignature,
"__wasm_apply_global_tls_relocs"));
WasmSym::applyGlobalTLSRelocs->markLive();
}
}
}