Replace all setjmp()/longjmp() with sigsetjmp()/siglongjmp()

The setjmp() function doesn't specify whether signal masks are saved and
restored; on Linux they are not, but on BSD (including MacOSX) they are.
We want to have consistent behaviour across platforms, so we should
always use "don't save/restore signal mask" (this is also generally
going to be faster). This also works around a bug in MacOSX where the
signal-restoration on longjmp() affects the signal mask for a completely
different thread, not just the mask for the thread which did the longjmp.
The most visible effect of this was that ctrl-C was ignored on MacOSX
because the CPU thread did a longjmp which resulted in its signal mask
being applied to every thread, so that all threads had SIGINT and SIGTERM
blocked.

The POSIX-sanctioned portable way to do a jump without affecting signal
masks is to siglongjmp() to a sigjmp_buf which was created by calling
sigsetjmp() with a zero savemask parameter, so change all uses of
setjmp()/longjmp() accordingly. [Technically POSIX allows sigsetjmp(buf, 0)
to save the signal mask; however the following siglongjmp() must not
restore the signal mask, so the pair can be effectively considered as
"sigjmp/longjmp which don't touch the mask".]

For Windows we provide a trivial sigsetjmp/siglongjmp in terms of
setjmp/longjmp -- this is OK because no user will ever pass a non-zero
savemask.

The setjmp() uses in tests/tcg/test-i386.c and tests/tcg/linux-test.c
are left untouched because these are self-contained singlethreaded
test programs intended to be run under QEMU's Linux emulation, so they
have neither the portability nor the multithreading issues to deal with.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <rth@twiddle.net>
Tested-by: Stefan Weil <sw@weilnetz.de>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>

2 files changed, 9 insertions, 1 deletions

diff --git a/include/exec/cpu-defs.h b/include/exec/cpu-defs.h
index ae64590cdf..3dc96568ac 100644
--- a/include/exec/cpu-defs.h
+++ b/include/exec/cpu-defs.h
@@ -184,7 +184,7 @@ typedef struct CPUWatchpoint {
     struct GDBRegisterState *gdb_regs;                                  \
                                                                         \
     /* Core interrupt code */                                           \
-    jmp_buf jmp_env;                                                    \
+    sigjmp_buf jmp_env;                                                 \
     int exception_index;                                                \
                                                                         \
     CPUArchState *next_cpu; /* next CPU sharing TB cache */                 \
diff --git a/include/sysemu/os-win32.h b/include/sysemu/os-win32.h
index bf9edeb9ab..71f5fa0a91 100644
--- a/include/sysemu/os-win32.h
+++ b/include/sysemu/os-win32.h
@@ -63,6 +63,14 @@
 # undef setjmp
 # define setjmp(env) _setjmp(env, NULL)
 #endif
+/* 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
+ * in terms of setjmp/longjmp on Win32.
+ */
+#define sigjmp_buf jmp_buf
+#define sigsetjmp(env, savemask) setjmp(env)
+#define siglongjmp(env, val) longjmp(env, val)
 
 /* Declaration of ffs() is missing in MinGW's strings.h. */
 int ffs(int i);