tcg: Fix error reporting on mprotect() failure in tcg_region_init()

tcg_region_init() calls one of qemu_mprotect_rwx(),
qemu_mprotect_rw(), and mprotect(), then reports failure with
error_setg_errno(&error_fatal, errno, ...).

The use of &error_fatal is undesirable.  qapi/error.h advises:

 * Please don't error_setg(&error_fatal, ...), use error_report() and
 * exit(), because that's more obvious.

The use of errno is wrong.  qemu_mprotect_rwx() and qemu_mprotect_rw()
wrap around qemu_mprotect__osdep().  qemu_mprotect__osdep() calls
mprotect() on POSIX, VirtualProtect() on Windows, and reports failure
with error_report().  VirtualProtect() doesn't set errno.  mprotect()
does, but error_report() may clobber it.

Fix tcg_region_init() to report errors only when it calls mprotect(),
and rely on qemu_mprotect_rwx()'s and qemu_mprotect_rw()'s error
reporting otherwise.  Use error_report(), not error_setg().

Fixes: 22c6a9938f (tcg: Merge buffer protection and guard page protection)
Fixes: 6bc144237a (tcg: Use Error with alloc_code_gen_buffer)
Cc: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-ID: <20250923091000.3180122-3-armbru@redhat.com>
Reviewed-by: Akihiko Odaki <odaki@rsg.ci.i.u-tokyo.ac.jp>

tcg/region.c

@@ -832,13 +832,16 @@ void tcg_region_init(size_t tb_size, int splitwx, unsigned max_threads)
             } else {
 #ifdef CONFIG_POSIX
                 rc = mprotect(start, end - start, need_prot);
+                if (rc) {
+                    error_report("mprotect of jit buffer: %s",
+                                 strerror(errno));
+                }
 #else
                 g_assert_not_reached();
 #endif
             }
             if (rc) {
-                error_setg_errno(&error_fatal, errno,
-                                 "mprotect of jit buffer");
+                exit(1);
             }
         }
         if (have_prot != 0) {