plugins: make test/example plugins work on windows

Generate a qemu_plugin_api.lib delay import lib on windows, for
windows qemu plugins to link against.

Implement an example dll load fail hook to link up the API functions
correctly when a plugin is loaded on windows.

Update the build scripts for the test and example plugins to use these
things.

Signed-off-by: Greg Manning <gmanning@rapitasystems.com>
Acked-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20231102172053.17692-3-gmanning@rapitasystems.com>
[AJB: use find_program for dlltool, s/Windows/windows/]
Cc: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20231106185112.2755262-15-alex.bennee@linaro.org>

configure

@@ -1666,6 +1666,9 @@ fi
 if test "$targetos" = darwin; then
   echo "CONFIG_DARWIN=y" >> contrib/plugins/$config_host_mak
 fi
+if test "$targetos" = windows; then
+  echo "CONFIG_WIN32=y" >> contrib/plugins/$config_host_mak
+fi
 
 # tests/tcg configuration
 (config_host_mak=tests/tcg/config-host.mak

contrib/plugins/Makefile

@@ -22,7 +22,14 @@ NAMES += hwprofile
 NAMES += cache
 NAMES += drcov
 
-SONAMES := $(addsuffix .so,$(addprefix lib,$(NAMES)))
+ifeq ($(CONFIG_WIN32),y)
+SO_SUFFIX := .dll
+LDLIBS += $(shell $(PKG_CONFIG) --libs glib-2.0)
+else
+SO_SUFFIX := .so
+endif
+
+SONAMES := $(addsuffix $(SO_SUFFIX),$(addprefix lib,$(NAMES)))
 
 # The main QEMU uses Glib extensively so it's perfectly fine to use it
 # in plugins (which many example do).
@@ -35,15 +42,20 @@ all: $(SONAMES)
 %.o: %.c
 	$(CC) $(CFLAGS) $(PLUGIN_CFLAGS) -c -o $@ $<
 
-lib%.so: %.o
-ifeq ($(CONFIG_DARWIN),y)
+ifeq ($(CONFIG_WIN32),y)
+lib%$(SO_SUFFIX): %.o win32_linker.o ../../plugins/qemu_plugin_api.lib
+	$(CC) -shared -o $@ $^ $(LDLIBS)
+else ifeq ($(CONFIG_DARWIN),y)
+lib%$(SO_SUFFIX): %.o
 	$(CC) -bundle -Wl,-undefined,dynamic_lookup -o $@ $^ $(LDLIBS)
 else
+lib%$(SO_SUFFIX): %.o
 	$(CC) -shared -o $@ $^ $(LDLIBS)
 endif
 
+
 clean:
-	rm -f *.o *.so *.d
+	rm -f *.o *$(SO_SUFFIX) *.d
 	rm -Rf .libs
 
 .PHONY: all clean

contrib/plugins/win32_linker.c

@@ -0,0 +1,34 @@
+/*
+ * Copyright (C) 2023, Greg Manning <gmanning@rapitasystems.com>
+ *
+ * This hook, __pfnDliFailureHook2, is documented in the microsoft documentation here:
+ * https://learn.microsoft.com/en-us/cpp/build/reference/error-handling-and-notification
+ * It gets called when a delay-loaded DLL encounters various errors.
+ * We handle the specific case of a DLL looking for a "qemu.exe",
+ * and give it the running executable (regardless of what it is named).
+ *
+ * This work is licensed under the terms of the GNU LGPL, version 2 or later.
+ * See the COPYING.LIB file in the top-level directory.
+ */
+
+#include <windows.h>
+#include <delayimp.h>
+
+FARPROC WINAPI dll_failure_hook(unsigned dliNotify, PDelayLoadInfo pdli);
+
+
+PfnDliHook __pfnDliFailureHook2 = dll_failure_hook;
+
+FARPROC WINAPI dll_failure_hook(unsigned dliNotify, PDelayLoadInfo pdli) {
+    if (dliNotify == dliFailLoadLib) {
+        /* If the failing request was for qemu.exe, ... */
+        if (strcmp(pdli->szDll, "qemu.exe") == 0) {
+            /* Then pass back a pointer to the top level module. */
+            HMODULE top = GetModuleHandle(NULL);
+            return (FARPROC) top;
+        }
+    }
+    /* Otherwise we can't do anything special. */
+    return 0;
+}
+

plugins/meson.build

@@ -14,6 +14,25 @@ if not enable_modules
 endif
 
 if get_option('plugins')
+  if targetos == 'windows'
+    dlltool = find_program('dlltool', required: true)
+
+    # Generate a .lib file for plugins to link against.
+    # First, create a .def file listing all the symbols a plugin should expect to have
+    # available in qemu
+    win32_plugin_def = configure_file(
+      input: files('qemu-plugins.symbols'),
+      output: 'qemu_plugin_api.def',
+      capture: true,
+      command: ['sed', '-e', '0,/^/s//EXPORTS/; s/[{};]//g', '@INPUT@'])
+    # then use dlltool to assemble a delaylib.
+    win32_qemu_plugin_api_lib = configure_file(
+      input: win32_plugin_def,
+      output: 'qemu_plugin_api.lib',
+      command: [dlltool, '--input-def', '@INPUT@',
+                '--output-delaylib', '@OUTPUT@', '--dllname', 'qemu.exe']
+    )
+  endif
   specific_ss.add(files(
     'loader.c',
     'core.c',

tests/plugin/meson.build

@@ -1,9 +1,17 @@
 t = []
 if get_option('plugins')
   foreach i : ['bb', 'empty', 'insn', 'mem', 'syscall']
-    t += shared_module(i, files(i + '.c'),
-                       include_directories: '../../include/qemu',
-                       dependencies: glib)
+    if targetos == 'windows'
+      t += shared_module(i, files(i + '.c') + '../../contrib/plugins/win32_linker.c',
+                        include_directories: '../../include/qemu',
+                        objects: [win32_qemu_plugin_api_lib],
+                        dependencies: glib)
+
+    else
+      t += shared_module(i, files(i + '.c'),
+                        include_directories: '../../include/qemu',
+                        dependencies: glib)
+    endif
   endforeach
 endif
 if t.length() > 0