[llvm-branch-commits] [lld] 1095870 - [wasm-ld] Define a `__heap_end` symbol marking the end of allocated memory.
Tom Stellard via llvm-branch-commits
llvm-branch-commits at lists.llvm.org
Tue Jan 10 17:02:51 PST 2023
Author: Dan Gohman
Date: 2023-01-10T17:01:48-08:00
New Revision: 1095870e8ceddc5371f446f4e7c3473f89a461cd
URL: https://github.com/llvm/llvm-project/commit/1095870e8ceddc5371f446f4e7c3473f89a461cd
DIFF: https://github.com/llvm/llvm-project/commit/1095870e8ceddc5371f446f4e7c3473f89a461cd.diff
LOG: [wasm-ld] Define a `__heap_end` symbol marking the end of allocated memory.
Define a `__heap_end` symbol that marks the end of the memory region
that starts at `__heap_base`. This will allow malloc implementations to
know how much memory they can use at `__heap_base` even if someone has
done a `memory.grow` before they can initialize their state.
Differential Revision: https://reviews.llvm.org/D136110
Added:
Modified:
lld/test/wasm/export-all.s
lld/test/wasm/mutable-global-exports.s
lld/wasm/Driver.cpp
lld/wasm/Symbols.cpp
lld/wasm/Symbols.h
lld/wasm/Writer.cpp
Removed:
################################################################################
diff --git a/lld/test/wasm/export-all.s b/lld/test/wasm/export-all.s
index 009da9f6a3817..5af835ce485e2 100644
--- a/lld/test/wasm/export-all.s
+++ b/lld/test/wasm/export-all.s
@@ -40,9 +40,12 @@ foo:
# CHECK-NEXT: - Name: __heap_base
# CHECK-NEXT: Kind: GLOBAL
# CHECK-NEXT: Index: 4
-# CHECK-NEXT: - Name: __memory_base
+# CHECK-NEXT: - Name: __heap_end
# CHECK-NEXT: Kind: GLOBAL
# CHECK-NEXT: Index: 5
-# CHECK-NEXT: - Name: __table_base
+# CHECK-NEXT: - Name: __memory_base
# CHECK-NEXT: Kind: GLOBAL
# CHECK-NEXT: Index: 6
+# CHECK-NEXT: - Name: __table_base
+# CHECK-NEXT: Kind: GLOBAL
+# CHECK-NEXT: Index: 7
diff --git a/lld/test/wasm/mutable-global-exports.s b/lld/test/wasm/mutable-global-exports.s
index e2e45ff93a4bc..98009610ac55f 100644
--- a/lld/test/wasm/mutable-global-exports.s
+++ b/lld/test/wasm/mutable-global-exports.s
@@ -79,10 +79,13 @@ _start:
# CHECK-ALL-NEXT: - Name: __heap_base
# CHECK-ALL-NEXT: Kind: GLOBAL
# CHECK-ALL-NEXT: Index: 5
-# CHECK-ALL-NEXT: - Name: __memory_base
+# CHECK-ALL-NEXT: - Name: __heap_end
# CHECK-ALL-NEXT: Kind: GLOBAL
# CHECK-ALL-NEXT: Index: 6
-# CHECK-ALL-NEXT: - Name: __table_base
+# CHECK-ALL-NEXT: - Name: __memory_base
# CHECK-ALL-NEXT: Kind: GLOBAL
# CHECK-ALL-NEXT: Index: 7
+# CHECK-ALL-NEXT: - Name: __table_base
+# CHECK-ALL-NEXT: Kind: GLOBAL
+# CHECK-ALL-NEXT: Index: 8
# CHECK-ALL-NEXT: - Type: CODE
diff --git a/lld/wasm/Driver.cpp b/lld/wasm/Driver.cpp
index 0a0f0c8a05bd7..4afbfe24110f8 100644
--- a/lld/wasm/Driver.cpp
+++ b/lld/wasm/Driver.cpp
@@ -681,6 +681,7 @@ static void createOptionalSymbols() {
if (!config->isPic) {
WasmSym::globalBase = symtab->addOptionalDataSymbol("__global_base");
WasmSym::heapBase = symtab->addOptionalDataSymbol("__heap_base");
+ WasmSym::heapEnd = symtab->addOptionalDataSymbol("__heap_end");
WasmSym::definedMemoryBase = symtab->addOptionalDataSymbol("__memory_base");
WasmSym::definedTableBase = symtab->addOptionalDataSymbol("__table_base");
if (config->is64.value_or(false))
diff --git a/lld/wasm/Symbols.cpp b/lld/wasm/Symbols.cpp
index e0670cea6425e..a79c5bec3b3bb 100644
--- a/lld/wasm/Symbols.cpp
+++ b/lld/wasm/Symbols.cpp
@@ -83,6 +83,7 @@ DefinedData *WasmSym::dsoHandle;
DefinedData *WasmSym::dataEnd;
DefinedData *WasmSym::globalBase;
DefinedData *WasmSym::heapBase;
+DefinedData *WasmSym::heapEnd;
DefinedData *WasmSym::initMemoryFlag;
GlobalSymbol *WasmSym::stackPointer;
GlobalSymbol *WasmSym::tlsBase;
diff --git a/lld/wasm/Symbols.h b/lld/wasm/Symbols.h
index c17b720a90fae..32e75a69c5f80 100644
--- a/lld/wasm/Symbols.h
+++ b/lld/wasm/Symbols.h
@@ -538,11 +538,14 @@ struct WasmSym {
// Symbol marking the end of the data and bss.
static DefinedData *dataEnd;
- // __heap_base
- // Symbol marking the end of the data, bss and explicit stack. Any linear
- // memory following this address is not used by the linked code and can
- // therefore be used as a backing store for brk()/malloc() implementations.
+ // __heap_base/__heap_end
+ // Symbols marking the beginning and end of the "heap". It starts at the end
+ // of the data, bss and explicit stack, and extends to the end of the linear
+ // memory allocated by wasm-ld. This region of memory is not used by the
+ // linked code, so it may be used as a backing store for `sbrk` or `malloc`
+ // implementations.
static DefinedData *heapBase;
+ static DefinedData *heapEnd;
// __wasm_init_memory_flag
// Symbol whose contents are nonzero iff memory has already been initialized.
diff --git a/lld/wasm/Writer.cpp b/lld/wasm/Writer.cpp
index f98c95526c9e0..f6bbaa02b571d 100644
--- a/lld/wasm/Writer.cpp
+++ b/lld/wasm/Writer.cpp
@@ -340,10 +340,20 @@ void Writer::layoutMemory() {
Twine(maxMemorySetting));
memoryPtr = config->initialMemory;
}
- out.memorySec->numMemoryPages =
- alignTo(memoryPtr, WasmPageSize) / WasmPageSize;
+
+ memoryPtr = alignTo(memoryPtr, WasmPageSize);
+
+ out.memorySec->numMemoryPages = memoryPtr / WasmPageSize;
log("mem: total pages = " + Twine(out.memorySec->numMemoryPages));
+ if (WasmSym::heapEnd) {
+ // Set `__heap_end` to follow the end of the statically allocated linear
+ // memory. The fact that this comes last means that a malloc/brk
+ // implementation can grow the heap at runtime.
+ log("mem: heap end = " + Twine(memoryPtr));
+ WasmSym::heapEnd->setVA(memoryPtr);
+ }
+
if (config->maxMemory != 0) {
if (config->maxMemory != alignTo(config->maxMemory, WasmPageSize))
error("maximum memory must be " + Twine(WasmPageSize) + "-byte aligned");
@@ -363,7 +373,7 @@ void Writer::layoutMemory() {
if (config->isPic)
max = maxMemorySetting;
else
- max = alignTo(memoryPtr, WasmPageSize);
+ max = memoryPtr;
}
out.memorySec->maxMemoryPages = max / WasmPageSize;
log("mem: max pages = " + Twine(out.memorySec->maxMemoryPages));
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