semihosting: add guest_error logging for failed opens

This usually indicates the semihosting call was expecting to find
something but didn't.

Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20250116160306.1709518-2-alex.bennee@linaro.org>

semihosting/syscalls.c

@@ -7,6 +7,7 @@
  */
 
 #include "qemu/osdep.h"
+#include "qemu/log.h"
 #include "cpu.h"
 #include "gdbstub/syscalls.h"
 #include "semihosting/guestfd.h"
@@ -287,6 +288,7 @@ static void host_open(CPUState *cs, gdb_syscall_complete_cb complete,
 
     ret = open(p, host_flags, mode);
     if (ret < 0) {
+        qemu_log_mask(LOG_GUEST_ERROR, "%s: failed to open %s\n", __func__, p);
         complete(cs, -1, errno);
     } else {
         int guestfd = alloc_guestfd();