[WebAssembly] Fix __init_tls_base global in coop threading (#208597)
This commit updates how `wasm-ld` initializes the `__init_tls_base` global during module instantiation. Previously this global was left entirely unmodified meaning that it was always 0. This change updates the `__wasm_init_memory` function to set this global dynamically in PIC mode based on the TLS address calculation, or in non-PIC mode the generation of `__wasm_init_memory` correctly sets it to the desired TLS address. cc https://github.com/WebAssembly/wasi-libc/issues/819
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Alex Crichton authored and 
Douglas Yung committed
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@@ -94,6 +94,28 @@ baz:
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# CHECK-NEXT: - Minimum: 0x2
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# CHECK-NOT: Shared
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# Ensure __init_stack_pointer, __init_tls_base, and __tls_size are all correct.
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# CHECK: - Type: GLOBAL
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# CHECK-NEXT: Globals:
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# CHECK-NEXT: - Index: 0
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# CHECK-NEXT: Type: I32
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# CHECK-NEXT: Mutable: false
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# CHECK-NEXT: InitExpr:
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# CHECK-NEXT: Opcode: I32_CONST
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# CHECK-NEXT: Value: 65536
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# CHECK-NEXT: - Index: 1
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# CHECK-NEXT: Type: I32
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# CHECK-NEXT: Mutable: true
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# CHECK-NEXT: InitExpr:
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# CHECK-NEXT: Opcode: I32_CONST
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# CHECK-NEXT: Value: 65544
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# CHECK-NEXT: - Index: 2
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# CHECK-NEXT: Type: I32
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# CHECK-NEXT: Mutable: false
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# CHECK-NEXT: InitExpr:
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# CHECK-NEXT: Opcode: I32_CONST
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# CHECK-NEXT: Value: 8
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# The function table is exported by default.
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# CHECK: - Type: EXPORT
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# CHECK: - Name: __indirect_function_table
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@@ -137,8 +159,14 @@ baz:
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# CHECK-NEXT: Name: __tls_align
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# DIS-LABEL: <__wasm_init_memory>:
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# DIS: memory.init 2, 0
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# DIS-NEXT: end
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# DIS-EMPTY:
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# DIS-NEXT: i32.const 65544
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# DIS-NEXT: i32.const 65544
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# DIS-NEXT: call 0
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# DIS-NEXT: i32.const 0
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# DIS-NEXT: i32.const 8
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# DIS-NEXT: memory.init 2, 0
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# DIS-NEXT: end
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# DIS-LABEL: <_start>:
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# DIS-EMPTY:
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@@ -168,6 +196,35 @@ baz:
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# RUN: obj2yaml %t.so | FileCheck %s --check-prefix=PIC
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# RUN: llvm-objdump --disassemble-symbols=__wasm_init_memory --no-show-raw-insn --no-leading-addr %t.so | FileCheck %s --check-prefix=PIC-DIS
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# The stack pointer is imported under the libcall ABI name and
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# __wasm_set_tls_base is imported for TLS initialization.
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# PIC: - Type: IMPORT
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# PIC: Field: __init_stack_pointer
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# PIC-NEXT: Kind: GLOBAL
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# PIC-NEXT: GlobalType: I32
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# PIC-NEXT: GlobalMutable: false
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# PIC: Field: __memory_base
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# PIC: Field: __table_base
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# PIC: Field: __wasm_set_tls_base
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# PIC-NEXT: Kind: FUNCTION
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# The PIC `__init_tls_base` global (global 3) is mutable and initialized ot
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# 0 since its final value is calculated once `__memory_base` is provided.
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# PIC: - Type: GLOBAL
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# PIC-NEXT: Globals:
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# PIC-NEXT: - Index: 3
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# PIC-NEXT: Type: I32
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# PIC-NEXT: Mutable: true
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# PIC-NEXT: InitExpr:
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# PIC-NEXT: Opcode: I32_CONST
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# PIC-NEXT: Value: 0
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# PIC-NEXT: - Index: 4
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# PIC-NEXT: Type: I32
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# PIC-NEXT: Mutable: false
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# PIC-NEXT: InitExpr:
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# PIC-NEXT: Opcode: I32_CONST
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# PIC-NEXT: Value: 8
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# In PIC mode the active .rodata and .data segments are combined into a single
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# active segment at __memory_base; the TLS segment remains passive.
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# PIC: - Type: DATACOUNT
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@@ -185,15 +242,32 @@ baz:
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# PIC-NEXT: Content: '0100000002000000'
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# PIC-NEXT: - Type: CUSTOM
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# PIC: GlobalNames:
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# PIC-NEXT: - Index: 0
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# PIC-NEXT: Name: __init_stack_pointer
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# PIC-NEXT: - Index: 1
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# PIC-NEXT: Name: __memory_base
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# PIC-NEXT: - Index: 2
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# PIC-NEXT: Name: __table_base
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# PIC-NEXT: - Index: 3
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# PIC-NEXT: Name: __init_tls_base
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# PIC-NEXT: - Index: 4
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# PIC-NEXT: Name: __tls_size
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# PIC-NEXT: - Index: 5
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# PIC-NEXT: Name: __tls_align
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# Memory initialization in PIC mode has a few responsibilities: it calculates
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# the TLS address and puts it in a local, `__wasm_set_tls_base` is called,
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# TLS is initialized, and then finally BSS is zero'd out.
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# the TLS address and puts it in a local, stores it into the __init_tls_base
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# global, `__wasm_set_tls_base` is called, TLS is initialized, and then finally
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# BSS is zero'd out.
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# PIC-DIS: <__wasm_init_memory>:
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# PIC-DIS-NEXT: .local i32
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# PIC-DIS-NEXT: i32.const 8
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# PIC-DIS-NEXT: global.get {{[0-9]+}}
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# PIC-DIS-NEXT: global.get 1
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# PIC-DIS-NEXT: i32.add
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# PIC-DIS-NEXT: local.tee 0
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# PIC-DIS-NEXT: local.get 0
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# PIC-DIS-NEXT: global.set 3
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# PIC-DIS-NEXT: call {{[0-9]+}}
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# PIC-DIS-NEXT: local.get 0
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# PIC-DIS-NEXT: i32.const 0
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+2
-3
@@ -981,9 +981,8 @@ static void createSyntheticSymbols() {
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// TLS symbols are all hidden/dso-local
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auto tls_base_name =
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ctx.arg.libcallThreadContext ? "__init_tls_base" : "__tls_base";
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ctx.sym.tlsBase =
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createGlobalVariable(tls_base_name, !ctx.arg.libcallThreadContext,
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WASM_SYMBOL_VISIBILITY_HIDDEN);
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ctx.sym.tlsBase = createGlobalVariable(tls_base_name, true,
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WASM_SYMBOL_VISIBILITY_HIDDEN);
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ctx.sym.tlsSize = createGlobalVariable("__tls_size", false,
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WASM_SYMBOL_VISIBILITY_HIDDEN);
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ctx.sym.tlsAlign = createGlobalVariable("__tls_align", false,
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@@ -1416,13 +1416,29 @@ void Writer::createInitMemoryFunction() {
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// When we initialize the TLS segment we also set the TLS base.
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// This allows the runtime to use this static copy of the TLS data
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// for the first/main thread.
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//
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// Note that for `--cooperative-threading` this additionally configures
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// the `__init_tls_base` global which is the initial TLS value that can
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// be used for all new component model tasks. For non-PIC builds this
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// global's statically known value is now calculated, so it's updated
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// here. For PIC builds the result of the address computation above is
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// what's stored into the global.
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if (ctx.arg.isMultithreaded() && s->isTLS()) {
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if (ctx.isPic) {
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// Cache the result of the addition in the TLS address local
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writeU8(os, WASM_OPCODE_LOCAL_TEE, "local.tee");
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writeUleb128(os, tlsAddressLocal, "tls address local");
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if (ctx.arg.libcallThreadContext) {
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writeU8(os, WASM_OPCODE_LOCAL_GET, "local.get");
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writeUleb128(os, tlsAddressLocal, "tls address local");
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writeU8(os, WASM_OPCODE_GLOBAL_SET, "global.set");
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writeUleb128(os, ctx.sym.tlsBase->getGlobalIndex(),
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"__init_tls_base");
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}
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} else {
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writePtrConst(os, s->startVA, is64, "destination address");
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if (ctx.arg.libcallThreadContext)
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ctx.sym.tlsBase->global->setPointerValue(s->startVA);
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}
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writeSetTLSBase(ctx, os);
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if (ctx.isPic) {
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