[PATCH 2/4] sysemu/os-win32: fix setjmp/longjmp on windows-arm64

[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.

Signed-off-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
---
 include/sysemu/os-win32.h | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/include/sysemu/os-win32.h b/include/sysemu/os-win32.h
index 5b38c7bd04..84f62d0a17 100644
--- a/include/sysemu/os-win32.h
+++ b/include/sysemu/os-win32.h
@@ -51,14 +51,28 @@ typedef struct sockaddr_un {
 extern "C" {
 #endif
 
-#if defined(_WIN64)
+#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 w64, 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. */
 # 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
-- 
2.30.2