[PULL v2 8/8] sysemu/os-win32: fix setjmp/longjmp on windows-arm64

[Richard Henderson <richard.henderson@linaro.org>]

From: Pierrick Bouvier <pierrick.bouvier@linaro.org>

Windows implementation of setjmp/longjmp is done in
C:/WINDOWS/system32/ucrtbase.dll. Alas, on arm64, it seems to *always*
perform stack unwinding, which crashes from generated code.

By using alternative implementation built in mingw, we avoid doing stack
unwinding and this fixes crash when calling longjmp.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Acked-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20230221153006.20300-3-pierrick.bouvier@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 include/sysemu/os-win32.h | 28 ++++++++++++++++++++++++----
 meson.build               | 21 +++++++++++++++++++++
 2 files changed, 45 insertions(+), 4 deletions(-)

diff --git a/include/sysemu/os-win32.h b/include/sysemu/os-win32.h
index 5b38c7bd04..97d0243aee 100644
--- a/include/sysemu/os-win32.h
+++ b/include/sysemu/os-win32.h
@@ -51,14 +51,34 @@ typedef struct sockaddr_un {
 extern "C" {
 #endif
 
-#if defined(_WIN64)
-/* On w64, setjmp is implemented by _setjmp which needs a second parameter.
+#if defined(__aarch64__)
+/*
+ * On windows-arm64, setjmp is available in only one variant, and longjmp always
+ * does stack unwinding. This crash with generated code.
+ * Thus, we use another implementation of setjmp (not windows one), coming from
+ * mingw, which never performs stack unwinding.
+ */
+#undef setjmp
+#undef longjmp
+/*
+ * These functions are not declared in setjmp.h because __aarch64__ defines
+ * setjmp to _setjmpex instead. However, they are still defined in libmingwex.a,
+ * which gets linked automatically.
+ */
+extern int __mingw_setjmp(jmp_buf);
+extern void __attribute__((noreturn)) __mingw_longjmp(jmp_buf, int);
+#define setjmp(env) __mingw_setjmp(env)
+#define longjmp(env, val) __mingw_longjmp(env, val)
+#elif defined(_WIN64)
+/*
+ * On windows-x64, setjmp is implemented by _setjmp which needs a second parameter.
  * If this parameter is NULL, longjump does no stack unwinding.
  * That is what we need for QEMU. Passing the value of register rsp (default)
- * lets longjmp try a stack unwinding which will crash with generated code. */
+ * lets longjmp try a stack unwinding which will crash with generated code.
+ */
 # undef setjmp
 # define setjmp(env) _setjmp(env, NULL)
-#endif
+#endif /* __aarch64__ */
 /* QEMU uses sigsetjmp()/siglongjmp() as the portable way to specify
  * "longjmp and don't touch the signal masks". Since we know that the
  * savemask parameter will always be zero we can safely define these
diff --git a/meson.build b/meson.build
index bc7e5b1d15..6a139e7085 100644
--- a/meson.build
+++ b/meson.build
@@ -2466,6 +2466,27 @@ if targetos == 'windows'
     }''', name: '_lock_file and _unlock_file'))
 endif
 
+if targetos == 'windows'
+  mingw_has_setjmp_longjmp = cc.links('''
+    #include <setjmp.h>
+    int main(void) {
+      /*
+       * These functions are not available in setjmp header, but may be
+       * available at link time, from libmingwex.a.
+       */
+      extern int __mingw_setjmp(jmp_buf);
+      extern void __attribute__((noreturn)) __mingw_longjmp(jmp_buf, int);
+      jmp_buf env;
+      __mingw_setjmp(env);
+      __mingw_longjmp(env, 0);
+    }
+  ''', name: 'mingw setjmp and longjmp')
+
+  if cpu == 'aarch64' and not mingw_has_setjmp_longjmp
+    error('mingw must provide setjmp/longjmp for windows-arm64')
+  endif
+endif
+
 ########################
 # Target configuration #
 ########################
-- 
2.34.1