meson: Add wasm build in build scripts

has_int128_type is set to false on emscripten as of now to avoid errors by
libffi. Tests are disabled on emscripten because they rely on host
features that aren't supported by emscripten (e.g. fork and unix
socket).

Signed-off-by: Kohei Tokunaga <ktokunaga.mail@gmail.com>
Link: https://lore.kernel.org/r/ad03b3b180335f59e785e930968077bf15c46260.1745820062.git.ktokunaga.mail@gmail.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

MAINTAINERS

@@ -634,6 +634,7 @@ S: Maintained
 F: include/system/os-wasm.h
 F: os-wasm.c
 F: util/coroutine-wasm.c
+F: configs/meson/emscripten.txt
 
 Alpha Machines
 --------------

configs/meson/emscripten.txt

@@ -0,0 +1,8 @@
+[built-in options]
+c_args = ['-pthread']
+cpp_args = ['-pthread']
+objc_args = ['-pthread']
+# -sPROXY_TO_PTHREAD link time flag always requires -pthread even during
+# configuration so explicitly add the flag here.
+c_link_args = ['-pthread','-sASYNCIFY=1','-sPROXY_TO_PTHREAD=1','-sFORCE_FILESYSTEM','-sALLOW_TABLE_GROWTH','-sTOTAL_MEMORY=2GB','-sWASM_BIGINT','-sEXPORT_ES6=1','-sASYNCIFY_IMPORTS=ffi_call_js','-sEXPORTED_RUNTIME_METHODS=addFunction,removeFunction,TTY,FS']
+cpp_link_args = ['-pthread','-sASYNCIFY=1','-sPROXY_TO_PTHREAD=1','-sFORCE_FILESYSTEM','-sALLOW_TABLE_GROWTH','-sTOTAL_MEMORY=2GB','-sWASM_BIGINT','-sEXPORT_ES6=1','-sASYNCIFY_IMPORTS=ffi_call_js','-sEXPORTED_RUNTIME_METHODS=addFunction,removeFunction,TTY,FS']

configure

@@ -360,6 +360,10 @@ elif check_define __NetBSD__; then
   host_os=netbsd
 elif check_define __APPLE__; then
   host_os=darwin
+elif check_define EMSCRIPTEN ; then
+  host_os=emscripten
+  cpu=wasm32
+  cross_compile="yes"
 else
   # This is a fatal error, but don't report it yet, because we
   # might be going to just print the --help text, or it might
@@ -526,6 +530,9 @@ case "$cpu" in
     linux_arch=x86
     CPU_CFLAGS="-m64"
     ;;
+  wasm32)
+    CPU_CFLAGS="-m32"
+    ;;
 esac
 
 if test -n "$host_arch" && {

meson.build

@@ -50,9 +50,9 @@ genh = []
 qapi_trace_events = []
 
 bsd_oses = ['gnu/kfreebsd', 'freebsd', 'netbsd', 'openbsd', 'dragonfly', 'darwin']
-supported_oses = ['windows', 'freebsd', 'netbsd', 'openbsd', 'darwin', 'sunos', 'linux']
+supported_oses = ['windows', 'freebsd', 'netbsd', 'openbsd', 'darwin', 'sunos', 'linux', 'emscripten']
 supported_cpus = ['ppc', 'ppc64', 's390x', 'riscv32', 'riscv64', 'x86', 'x86_64',
-  'arm', 'aarch64', 'loongarch64', 'mips', 'mips64', 'sparc64']
+  'arm', 'aarch64', 'loongarch64', 'mips', 'mips64', 'sparc64', 'wasm32']
 
 cpu = host_machine.cpu_family()
 
@@ -353,6 +353,8 @@ foreach lang : all_languages
       # endif
       #endif''')
     # ok
+  elif compiler.get_id() == 'emscripten'
+    # ok
   else
     error('You either need GCC v7.4 or Clang v10.0 (or XCode Clang v15.0) to compile QEMU')
   endif
@@ -470,7 +472,10 @@ endif
 # instead, we can't add -no-pie because it overrides -shared: the linker then
 # tries to build an executable instead of a shared library and fails.  So
 # don't add -no-pie anywhere and cross fingers. :(
-if not get_option('b_pie')
+#
+# Emscripten doesn't support -no-pie but meson can't catch the compiler
+# warning. So explicitly omit the flag for Emscripten.
+if not get_option('b_pie') and host_os != 'emscripten'
   qemu_common_flags += cc.get_supported_arguments('-fno-pie', '-no-pie')
 endif
 
@@ -514,6 +519,8 @@ ucontext_probe = '''
 supported_backends = []
 if host_os == 'windows'
   supported_backends += ['windows']
+elif host_os == 'emscripten'
+  supported_backends += ['wasm']
 else
   if host_os != 'darwin' and cc.links(ucontext_probe)
     supported_backends += ['ucontext']
@@ -902,6 +909,10 @@ if get_option('tcg').allowed()
     if not get_option('tcg_interpreter')
       error('Unsupported CPU @0@, try --enable-tcg-interpreter'.format(cpu))
     endif
+  elif host_arch == 'wasm32'
+    if not get_option('tcg_interpreter')
+      error('WebAssembly host requires --enable-tcg-interpreter')
+    endif
   elif get_option('tcg_interpreter')
     warning('Use of the TCG interpreter is not recommended on this host')
     warning('architecture. There is a native TCG execution backend available')
@@ -2962,7 +2973,9 @@ config_host_data.set('CONFIG_ATOMIC64', cc.links('''
     return 0;
   }''', args: qemu_isa_flags))
 
-has_int128_type = cc.compiles('''
+# has_int128_type is set to false on Emscripten to avoid errors by libffi
+# during runtime.
+has_int128_type = host_os != 'emscripten' and cc.compiles('''
   __int128_t a;
   __uint128_t b;
   int main(void) { b = a; }''')
@@ -3775,6 +3788,8 @@ if have_block
   # os-win32.c does not
   if host_os == 'windows'
     system_ss.add(files('os-win32.c'))
+  elif host_os == 'emscripten'
+    blockdev_ss.add(files('os-wasm.c'))
   else
     blockdev_ss.add(files('os-posix.c'))
   endif
@@ -4516,7 +4531,11 @@ subdir('scripts')
 subdir('tools')
 subdir('pc-bios')
 subdir('docs')
-subdir('tests')
+# Tests are disabled on emscripten because they rely on host features that aren't
+# supported by emscripten (e.g. fork and unix socket).
+if host_os != 'emscripten'
+  subdir('tests')
+endif
 if gtk.found()
   subdir('po')
 endif

meson_options.txt

@@ -34,7 +34,7 @@ option('fuzzing_engine', type : 'string', value : '',
 option('trace_file', type: 'string', value: 'trace',
        description: 'Trace file prefix for simple backend')
 option('coroutine_backend', type: 'combo',
-       choices: ['ucontext', 'sigaltstack', 'windows', 'auto'],
+       choices: ['ucontext', 'sigaltstack', 'windows', 'wasm', 'auto'],
        value: 'auto', description: 'coroutine backend to use')
 
 # Everything else can be set via --enable/--disable-* option

scripts/meson-buildoptions.sh

@@ -80,7 +80,7 @@ meson_options_help() {
   printf "%s\n" '  --tls-priority=VALUE     Default TLS protocol/cipher priority string'
   printf "%s\n" '                           [NORMAL]'
   printf "%s\n" '  --with-coroutine=CHOICE  coroutine backend to use (choices:'
-  printf "%s\n" '                           auto/sigaltstack/ucontext/windows)'
+  printf "%s\n" '                           auto/sigaltstack/ucontext/windows/wasm)'
   printf "%s\n" '  --with-pkgversion=VALUE  use specified string as sub-version of the'
   printf "%s\n" '                           package'
   printf "%s\n" '  --with-suffix=VALUE      Suffix for QEMU data/modules/config directories'