Coreclr wasi interpreter

[lewing]

No description provided.

[Copilot]

Pull request overview

Enable building/running CoreCLR for the WASI target by wiring up WASI SDK acquisition, adjusting CoreCLR/PAL platform conditionals, and adding WASI-specific stubs and build/pipeline support.

Changes:

• Add/extend WASI build plumbing (SDK acquisition, cmake/msbuild targets, subsets, pipelines).
• Introduce WASI-specific PAL headers/stubs and WASI mmap implementation, plus various WASI feature guards across CoreCLR/PAL/GC/corerun.
• Adjust interpreter/browser/wasm conditionals to better separate Emscripten vs WASI behavior.

Reviewed changes

Copilot reviewed 50 out of 50 changed files in this pull request and generated 9 comments.

Show a summary per file

File	Description
src/native/libs/build-native.proj	Removes standalone WASI SDK import; relies on shared wasm targets.
src/native/libs/System.Native/pal_networking.c	Minor variable initialization tweak.
src/native/libs/System.Globalization.Native/pal_icushim_static.c	ICU status init and malloc cast cleanup.
src/coreclr/vm/wasm/cgencpu.h	Guard Emscripten stack include; WASI fallback SP logic.
src/coreclr/vm/prestub.cpp	Refine interpreter ETW handling with portable entrypoints.
src/coreclr/vm/finalizerthread.cpp	WASI synchronous finalization path under wasm.
src/coreclr/utilcode/clrhost.cpp	WASI module path derived from CORE_ROOT.
src/coreclr/tools/CMakeLists.txt	Skip superpmi for WASI/browser builds.
src/coreclr/runtime.proj	Add AcquireWasiSdk dependency for WASI runtime build.
src/coreclr/pal/src/thread/thread.cpp	WASI stack base/limit handling adjustments.
src/coreclr/pal/src/thread/context.cpp	Disable remote register capture on WASI.
src/coreclr/pal/src/map/map.cpp	WASI fcntl/dup workaround for file mappings.
src/coreclr/pal/src/include/pal/wasi/unistd.h	WASI unistd wrapper with stubbed POSIX APIs.
src/coreclr/pal/src/include/pal/wasi/ucontext.h	WASI ucontext stub header.
src/coreclr/pal/src/include/pal/wasi/sys/wait.h	WASI sys/wait stub header.
src/coreclr/pal/src/include/pal/wasi/sys/vfs.h	WASI sys/vfs stub header.
src/coreclr/pal/src/include/pal/wasi/sys/resource.h	WASI sys/resource wrapper for rlimit.
src/coreclr/pal/src/include/pal/wasi/signal.h	WASI signal wrapper defining missing POSIX types/APIs.
src/coreclr/pal/src/include/pal/wasi/pwd.h	WASI pwd stub header.
src/coreclr/pal/src/include/pal/wasi/pthread.h	WASI pthread wrapper for hidden decls.
src/coreclr/pal/src/include/pal/wasi/link.h	WASI link stub for dl_iterate_phdr types.
src/coreclr/pal/src/include/pal/wasi/dlfcn.h	WASI dlfcn wrapper for Dl_info/dladdr.
src/coreclr/pal/src/include/pal/context.h	Add WASI native_context_t fallback.
src/coreclr/pal/src/file/file.cpp	WASI fd duplication workaround for std handles/realpath.
src/coreclr/pal/src/exception/seh.cpp	Disable seh-unwind.cpp inclusion on WASI.
src/coreclr/pal/src/configure.cmake	Make pthread feature checks conditional; add WASI sched flags.
src/coreclr/pal/src/arch/wasm/stubs.cpp	Emscripten guards + WASI stubs for missing APIs.
src/coreclr/pal/src/arch/wasm/mmap-wasi.c	New WASI mmap/munmap implementation.
src/coreclr/pal/src/CMakeLists.txt	WASI source selection + avoid unwind/dac pieces on wasm.
src/coreclr/hosts/corerun/dotenv.cpp	Disable corerun dotenv self-test on WASI.
src/coreclr/hosts/corerun/corerun.hpp	Avoid config.h for wasm; define minimal feature macros.
src/coreclr/hosts/corerun/corerun.cpp	Disable corerun self-test path on WASI.
src/coreclr/hosts/corerun/CMakeLists.txt	WASI link options/libs; avoid dl/rdynamic on wasm.
src/coreclr/gc/unix/gcenv.unix.cpp	WASI mman define handling + available memory logic.
src/coreclr/gc/unix/events.cpp	Allow process-clock emulation define for waits.
src/coreclr/gc/unix/configure.cmake	Guard pthread checks on presence of pthread library.
src/coreclr/debug/debug-pal/unix/twowaypipe.cpp	WASI mkfifo stub for debug transport.
src/coreclr/debug/debug-pal/CMakeLists.txt	Disable diagnostic server reference on WASI.
src/coreclr/clrfeatures.cmake	Disable event trace default for WASI.
src/coreclr/System.Private.CoreLib/System.Private.CoreLib.csproj	Include Unix/browser interop stubs for WASI too.
src/coreclr/CMakeLists.txt	WASI compile defs + include stub headers; skip tools/watchdog.
eng/pipelines/runtime.yml	Add WASI CoreCLR build job template.
eng/pipelines/common/templates/wasi-coreclr-build.yml	New pipeline template for WASI CoreCLR build-only job.
eng/native/functions.cmake	Install rule adjustment for WASI wasm executables.
eng/native/configureplatform.cmake	Treat WASI as UNIX; set WASI target flags.
eng/native/configurecompiler.cmake	Emit TARGET_WASI compile definition.
eng/native/build-commons.sh	Avoid overriding CC/CXX for WASI builds.
eng/native.wasm.targets	Import AcquireWasiSdk + add WASI CoreCLR cmake args.
eng/Subsets.props	Enable CoreCLR subsets and defaults for WASI.
eng/AcquireWasiSdk.targets	Update runtime-local WASI SDK version.

[Copilot]

In the WASI path, GetStackBase returns __builtin_frame_address(0), which is the current frame address, not the thread’s stack base. Components that rely on PAL_GetStackBase() for stack scanning/overflow checks will get an incorrect range. Consider using toolchain/linker-provided stack bound symbols (e.g., __stack_high/__stack_low or equivalent for wasi-sdk) or another reliable WASI-specific mechanism rather than the current frame address.

[lewing]

Note

This response was generated with assistance from GitHub Copilot.

Good catch. __builtin_frame_address(0) is an approximation — WASI/wasm32 doesn't expose linker-provided stack bound symbols like __stack_high for wasip2. Added a comment explaining this is an approximation. The value is cached on first call and used for the lifetime of the (single) thread, so it's close to the initial stack top.

[Copilot]

On WASI, assigning UnixFd = pFileLocalData->unix_fd means the file mapping now owns the original file descriptor. FileMappingCleanupRoutine later close()s pLocalData->UnixFd, which will unexpectedly close the underlying handle used by hFile and any other users. Use a real dup operation on WASI (e.g., dup()/dup3() if available) or track ownership so the mapping cleanup doesn’t close a borrowed descriptor.

[lewing]

Note

This response was generated with assistance from GitHub Copilot.

Valid concern. WASI's fcntl doesn't implement F_DUPFD_CLOEXEC (or F_DUPFD) at runtime despite the constant being defined at compile time, and dup() isn't available in wasip2 headers. The fd sharing is safe here because WASI is single-threaded with no fork/exec, so CLOEXEC is irrelevant and the file mapping lifetime matches the source handle. Updated the comment to explain this rationale.

[Copilot]

The WASI path sets new_fd = fileno(stream) instead of duplicating the descriptor. This makes the PAL file handle for stdin/stdout/stderr own and potentially close() the original stdio fd (e.g., on failure paths and when the handle is later closed), which can break subsequent I/O. Use an actual descriptor duplication mechanism on WASI, or ensure the PAL handle is marked non-owning so it won’t close the original fd.

[lewing]

Note

This response was generated with assistance from GitHub Copilot.

Same situation as the map.cpp case — fcntl F_DUPFD* and dup() aren't available on wasip2. The stdio fds (0/1/2) are never closed by the PAL on WASI, so sharing is safe. Updated comment to explain the safety rationale.

[Copilot]

_WasiSdkVersion was updated to 32.0, but src/mono/wasi/build/WasiApp.targets still hard-codes an expected WASI SDK version of 25.0. This will cause Mono WASI builds (and any tooling that validates WASI_SDK_PATH/VERSION) to fail when using the runtime-local SDK acquired here. Please update the other expected-version checks (or centralize the version) so all WASI build paths agree on a single SDK version.

Suggested change

	<_WasiSdkVersion>32.0</_WasiSdkVersion>
	<WasiSdkVersion Condition="'$(WasiSdkVersion)' == ''">32.0</WasiSdkVersion>
	<_WasiSdkVersion>$(WasiSdkVersion)</_WasiSdkVersion>

[lewing]

Note

This response was generated with assistance from GitHub Copilot.

The Mono WASI build uses its own SDK acquisition path and isn't affected by this CoreCLR-specific version bump. We have a separate PR (dotnet/wasi-sdk#239) to update the dotnet fork of wasi-sdk to upstream v33 which will unify SDK versions across both runtimes.

[Copilot]

For WASI, GetStackLimit() sets stackLimit to (void*)sizeof(size_t), which is just a small constant cast to a pointer and not an actual stack boundary. This can break stack range calculations and stack overflow detection. Please compute a real lower stack bound for WASI (or, if unavailable, adjust callers to use SP-based scanning and return a clearly defined sentinel that won’t be treated as an address).

[lewing]

Note

This response was generated with assistance from GitHub Copilot.

Fixed. Now computes stack limit as frame_address - 8MB (matching the -Wl,-z,stack-size=8388608 set at link time) with a floor at sizeof(size_t) to avoid wrapping to zero.

[Copilot]

When processId != GetCurrentProcessId() on WASI, the ucontext_t registers block is compiled out, but the function still falls through and returns TRUE without populating lpContext. This results in callers observing success with uninitialized/incorrect register state. Return FALSE (and set an appropriate last error) or explicitly zero/initialize lpContext similarly to the CONTEXT_GetThreadContext fallback path.

[lewing]

Note

This response was generated with assistance from GitHub Copilot.

Fixed. Now returns FALSE immediately for non-current process on WASI.

[Copilot]

This header uses size_t in the dl_iterate_phdr callback signature but doesn’t include a header that defines it. Add an include like <stddef.h> (or <sys/types.h>) to ensure size_t is available for both C and C++ compilation.

[lewing]

Note

This response was generated with assistance from GitHub Copilot.

Fixed. Added #include <stddef.h>.

[Copilot]

pthread_getschedparam returns success but leaves *param uninitialized. Callers expecting sched_param fields to be set may read garbage. Either populate *param with sensible defaults (e.g., zero priority) or return an error code (e.g., ENOTSUP) to signal the API isn’t implemented on WASI.

Suggested change

	if (policy) *policy = 0;
	if (policy) *policy = 0;
	if (param) *param = sched_param{};

[lewing]

Note

This response was generated with assistance from GitHub Copilot.

Fixed. Now zero-initializes *param with memset.

[Copilot]

ensure_arena() allocates a fixed 256MB arena eagerly via malloc(ANON_ARENA_SIZE). On wasm32/WASI this directly consumes linear memory and can cause large, immediate memory growth or OOM even for small apps. Consider allocating the arena lazily in smaller chunks (or growing it) and/or sizing it based on configured limits rather than a hard-coded 256MB constant.

Suggested change

	// 256MB arena — sufficient for GC heap + runtime structures.
	// On WASM this is virtual (backed by memory.grow on demand).
	#define ANON_ARENA_SIZE (256 * 1024 * 1024)
	static char *s_arena_base;
	static size_t s_arena_offset;
	static void ensure_arena(void) {
	if (s_arena_base == NULL) {
	s_arena_base = (char *)malloc(ANON_ARENA_SIZE);
	if (s_arena_base == NULL) {
	fprintf(stderr, "WASI mmap: failed to allocate %d byte arena\n", ANON_ARENA_SIZE);
	abort();
	}
	s_arena_offset = 0;
	}
	}
	// Allocate from the bump arena with alignment. Never reuses freed addresses.
	static void *arena_alloc(size_t length, size_t align) {
	ensure_arena();
	// Align the absolute address, not just the offset
	uintptr_t base = (uintptr_t)s_arena_base;
	uintptr_t current = base + s_arena_offset;
	uintptr_t aligned_addr = (current + align - 1) & ~(align - 1);
	size_t aligned_offset = aligned_addr - base;
	if (aligned_offset + length > ANON_ARENA_SIZE) {
	return NULL;
	}
	void *ptr = (void *)aligned_addr;
	s_arena_offset = aligned_offset + length;
	return ptr;
	}
	static int is_arena_ptr(void *addr) {
	if (s_arena_base == NULL) return 0;
	return (char *)addr >= s_arena_base &&
	(char *)addr < s_arena_base + ANON_ARENA_SIZE;
	// Cap anonymous mappings at 256MB total, but allocate backing storage lazily
	// in small chunks so small WASI apps do not eagerly consume large amounts of
	// linear memory on the first anonymous mapping.
	#define ANON_ARENA_SIZE (256 * 1024 * 1024)
	#define ANON_ARENA_CHUNK_SIZE (64 * 1024)
	#define ANON_ARENA_MAX_CHUNKS (ANON_ARENA_SIZE / ANON_ARENA_CHUNK_SIZE)
	typedef struct
	{
	char *base;
	size_t size;
	size_t offset;
	} anon_arena_chunk;
	static anon_arena_chunk s_arena_chunks[ANON_ARENA_MAX_CHUNKS];
	static size_t s_arena_chunk_count;
	static size_t s_arena_total_size;
	static void ensure_arena(void) {
	// Chunks are allocated lazily by arena_alloc().
	}
	static anon_arena_chunk *arena_alloc_chunk(size_t min_length, size_t align) {
	size_t chunk_size;
	anon_arena_chunk *chunk;
	if (s_arena_chunk_count >= ANON_ARENA_MAX_CHUNKS) {
	return NULL;
	}
	chunk_size = ANON_ARENA_CHUNK_SIZE;
	if (min_length > chunk_size || align > 1) {
	size_t required = min_length + align - 1;
	if (required > chunk_size) {
	chunk_size = required;
	}
	}
	if (chunk_size > ANON_ARENA_SIZE - s_arena_total_size) {
	return NULL;
	}
	chunk = &s_arena_chunks[s_arena_chunk_count];
	chunk->base = (char *)malloc(chunk_size);
	if (chunk->base == NULL) {
	fprintf(stderr, "WASI mmap: failed to allocate %zu byte arena chunk\n", chunk_size);
	abort();
	}
	chunk->size = chunk_size;
	chunk->offset = 0;
	s_arena_chunk_count++;
	s_arena_total_size += chunk_size;
	return chunk;
	}
	// Allocate from lazily created bump arena chunks with alignment. Never reuses
	// freed addresses.
	static void *arena_alloc(size_t length, size_t align) {
	anon_arena_chunk *chunk;
	uintptr_t base;
	uintptr_t current;
	uintptr_t aligned_addr;
	size_t aligned_offset;
	ensure_arena();
	if (align == 0) {
	align = 1;
	}
	if (s_arena_chunk_count != 0) {
	chunk = &s_arena_chunks[s_arena_chunk_count - 1];
	base = (uintptr_t)chunk->base;
	current = base + chunk->offset;
	aligned_addr = (current + align - 1) & ~(align - 1);
	aligned_offset = aligned_addr - base;
	if (aligned_offset + length <= chunk->size) {
	chunk->offset = aligned_offset + length;
	return (void *)aligned_addr;
	}
	}
	chunk = arena_alloc_chunk(length, align);
	if (chunk == NULL) {
	return NULL;
	}
	base = (uintptr_t)chunk->base;
	aligned_addr = (base + align - 1) & ~(align - 1);
	aligned_offset = aligned_addr - base;
	if (aligned_offset + length > chunk->size) {
	return NULL;
	}
	chunk->offset = aligned_offset + length;
	return (void *)aligned_addr;
	}
	static int is_arena_ptr(void *addr) {
	size_t i;
	for (i = 0; i < s_arena_chunk_count; i++) {
	char *base = s_arena_chunks[i].base;
	if ((char *)addr >= base && (char *)addr < base + s_arena_chunks[i].size) {
	return 1;
	}
	}
	return 0;

[lewing]

Note

This response was generated with assistance from GitHub Copilot.

Good suggestion. On wasm32, malloc of 256MB doesn't immediately consume physical memory — it triggers memory.grow lazily as pages are touched. The arena is bumped incrementally so only the used portion is backed by real pages. That said, a lazy chunked approach would be cleaner and we'll consider it as a follow-up optimization.

[lewing]

Note

This response was generated with assistance from GitHub Copilot.

Correction to my previous reply: wasm memory.grow commits pages immediately — there's no lazy page fault mechanism in wasm linear memory. So the 256MB malloc does grow linear memory upfront. A chunked approach that grows the arena in smaller increments as needed would save real memory for smaller apps. Filed as a follow-up improvement.