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>

6 files changed, 42 insertions, 7 deletions

diff --git a/MAINTAINERS b/MAINTAINERS
index 55c47fc..02b75ea 100644
--- a/MAINTAINERS
+++ b/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
 --------------
diff --git a/configs/meson/emscripten.txt b/configs/meson/emscripten.txt
new file mode 100644
index 0000000..4230e88
--- /dev/null
+++ b/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']
diff --git a/configure b/configure
index 40705af..2ce8d29 100755
--- a/configure
+++ b/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" && {
diff --git a/meson.build b/meson.build
index 8eb3de5..27f1150 100644
--- a/meson.build
+++ b/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
diff --git a/meson_options.txt b/meson_options.txt
index 0b4115e..cc66b46 100644
--- a/meson_options.txt
+++ b/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
diff --git a/scripts/meson-buildoptions.sh b/scripts/meson-buildoptions.sh
index d76a239..8a67a14 100644
--- a/scripts/meson-buildoptions.sh
+++ b/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'