build: move coroutine backend selection to meson

To simplify the code, rename coroutine-win32.c to match the option
passed to configure.

Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

configure

@@ -282,7 +282,6 @@ softmmu="yes"
 linux_user=""
 bsd_user=""
 pie=""
-coroutine=""
 plugins="$default_feature"
 ninja=""
 bindir="bin"
@@ -843,8 +842,6 @@ for opt do
   ;;
   --enable-fdt=*) fdt="$optarg"
   ;;
-  --with-coroutine=*) coroutine="$optarg"
-  ;;
   --with-git=*) git="$optarg"
   ;;
   --with-git-submodules=*)
@@ -1003,8 +1000,6 @@ Advanced options (experts only):
   --disable-werror         disable compilation abort on warning
   --disable-stack-protector disable compiler-provided stack protection
   --cpu=CPU                Build for host CPU [$cpu]
-  --with-coroutine=BACKEND coroutine backend. Supported options:
-                           ucontext, sigaltstack, windows
   --enable-plugins
                            enable plugins via shared library loading
   --disable-containers     don't use containers for cross-building
@@ -1459,61 +1454,6 @@ case "$fdt" in
     ;;
 esac
 
-##########################################
-# check and set a backend for coroutine
-
-# We prefer ucontext, but it's not always possible. The fallback
-# is sigcontext. On Windows the only valid backend is the Windows
-# specific one.
-
-ucontext_works=no
-if test "$darwin" != "yes"; then
-  cat > $TMPC << EOF
-#include <ucontext.h>
-#ifdef __stub_makecontext
-#error Ignoring glibc stub makecontext which will always fail
-#endif
-int main(void) { makecontext(0, 0, 0); return 0; }
-EOF
-  if compile_prog "" "" ; then
-    ucontext_works=yes
-  fi
-fi
-
-if test "$coroutine" = ""; then
-  if test "$mingw32" = "yes"; then
-    coroutine=win32
-  elif test "$ucontext_works" = "yes"; then
-    coroutine=ucontext
-  else
-    coroutine=sigaltstack
-  fi
-else
-  case $coroutine in
-  windows)
-    if test "$mingw32" != "yes"; then
-      error_exit "'windows' coroutine backend only valid for Windows"
-    fi
-    # Unfortunately the user visible backend name doesn't match the
-    # coroutine-*.c filename for this case, so we have to adjust it here.
-    coroutine=win32
-    ;;
-  ucontext)
-    if test "$ucontext_works" != "yes"; then
-      error_exit "'ucontext' backend requested but makecontext not available"
-    fi
-    ;;
-  sigaltstack)
-    if test "$mingw32" = "yes"; then
-      error_exit "only the 'windows' coroutine backend is valid for Windows"
-    fi
-    ;;
-  *)
-    error_exit "unknown coroutine backend $coroutine"
-    ;;
-  esac
-fi
-
 ########################################
 # check if ccache is interfering with
 # semantic analysis of macros
@@ -2089,8 +2029,6 @@ if [ "$bsd" = "yes" ] ; then
   echo "CONFIG_BSD=y" >> $config_host_mak
 fi
 
-echo "CONFIG_COROUTINE_BACKEND=$coroutine" >> $config_host_mak
-
 if test "$plugins" = "yes" ; then
     echo "CONFIG_PLUGIN=y" >> $config_host_mak
 fi

meson.build

@@ -211,6 +211,34 @@ if get_option('prefer_static')
   qemu_ldflags += get_option('b_pie') ? '-static-pie' : '-static'
 endif
 
+coroutine_backend = get_option('coroutine_backend')
+ucontext_probe = '''
+  #include <ucontext.h>
+  #ifdef __stub_makecontext
+  #error Ignoring glibc stub makecontext which will always fail
+  #endif
+  int main(void) { makecontext(0, 0, 0); return 0; }'''
+
+# On Windows the only valid backend is the Windows specific one.
+# For POSIX prefer ucontext, but it's not always possible. The fallback
+# is sigcontext.
+supported_backends = []
+if targetos == 'windows'
+  supported_backends += ['windows']
+else
+  if targetos != 'darwin' and cc.links(ucontext_probe)
+    supported_backends += ['ucontext']
+  endif
+  supported_backends += ['sigaltstack']
+endif
+
+if coroutine_backend == 'auto'
+  coroutine_backend = supported_backends[0]
+elif coroutine_backend not in supported_backends
+  error('"@0@" backend requested but not available.  Available backends: @1@' \
+        .format(coroutine_backend, ', '.join(supported_backends)))
+endif
+
 # Compiles if SafeStack *not* enabled
 safe_stack_probe = '''
   int main(void)
@@ -232,7 +260,7 @@ if get_option('safe_stack') != not cc.compiles(safe_stack_probe)
   qemu_cflags += safe_stack_arg
   qemu_ldflags += safe_stack_arg
 endif
-if get_option('safe_stack') and config_host['CONFIG_COROUTINE_BACKEND'] != 'ucontext'
+if get_option('safe_stack') and coroutine_backend != 'ucontext'
   error('SafeStack is only supported with the ucontext coroutine backend')
 endif
 
@@ -4037,7 +4065,7 @@ summary(summary_info, bool_yn: true, section: 'Targets and accelerators')
 
 # Block layer
 summary_info = {}
-summary_info += {'coroutine backend': config_host['CONFIG_COROUTINE_BACKEND']}
+summary_info += {'coroutine backend': coroutine_backend}
 summary_info += {'coroutine pool':    have_coroutine_pool}
 if have_block
   summary_info += {'Block whitelist (rw)': get_option('block_drv_rw_whitelist')}

meson_options.txt

@@ -31,6 +31,9 @@ option('fuzzing_engine', type : 'string', value : '',
        description: 'fuzzing engine library for OSS-Fuzz')
 option('trace_file', type: 'string', value: 'trace',
        description: 'Trace file prefix for simple backend')
+option('coroutine_backend', type: 'combo',
+       choices: ['ucontext', 'sigaltstack', 'windows', 'auto'],
+       value: 'auto', description: 'coroutine backend to use')
 
 # Everything else can be set via --enable/--disable-* option
 # on the configure script command line.  After adding an option

scripts/meson-buildoptions.py

@@ -35,6 +35,7 @@ SKIP_OPTIONS = {
 OPTION_NAMES = {
     "b_coverage": "gcov",
     "b_lto": "lto",
+    "coroutine_backend": "with-coroutine",
     "malloc": "enable-malloc",
     "pkgversion": "with-pkgversion",
     "qemu_firmwarepath": "firmwarepath",

scripts/meson-buildoptions.sh

@@ -64,6 +64,8 @@ meson_options_help() {
   printf "%s\n" '  --sysconfdir=VALUE       Sysconf data directory [etc]'
   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" '  --with-pkgversion=VALUE  use specified string as sub-version of the'
   printf "%s\n" '                           package'
   printf "%s\n" '  --with-trace-file=VALUE  Trace file prefix for simple backend [trace]'
@@ -250,6 +252,7 @@ _meson_option_parse() {
     --disable-cocoa) printf "%s" -Dcocoa=disabled ;;
     --enable-coreaudio) printf "%s" -Dcoreaudio=enabled ;;
     --disable-coreaudio) printf "%s" -Dcoreaudio=disabled ;;
+    --with-coroutine=*) quote_sh "-Dcoroutine_backend=$2" ;;
     --enable-coroutine-pool) printf "%s" -Dcoroutine_pool=true ;;
     --disable-coroutine-pool) printf "%s" -Dcoroutine_pool=false ;;
     --enable-crypto-afalg) printf "%s" -Dcrypto_afalg=enabled ;;

util/meson.build

@@ -78,7 +78,7 @@ if have_block or have_ga
   util_ss.add(files('base64.c'))
   util_ss.add(files('main-loop.c'))
   util_ss.add(files('qemu-coroutine.c', 'qemu-coroutine-lock.c', 'qemu-coroutine-io.c'))
-  util_ss.add(files('coroutine-@0@.c'.format(config_host['CONFIG_COROUTINE_BACKEND'])))
+  util_ss.add(files(f'coroutine-@coroutine_backend@.c'))
   util_ss.add(files('thread-pool.c', 'qemu-timer.c'))
   util_ss.add(files('qemu-sockets.c'))
 endif