sim: callback: add a getpid interface

Rather than hit the OS interface directly, use the existing callback
layer so the instantiator can decide behavior.

include/sim/ChangeLog

@@ -1,3 +1,7 @@
+2021-06-22  Mike Frysinger  <vapier@gentoo.org>
+
+	* sim/callback.h (struct host_callback_struct): Add getpid.
+
 2021-05-14  Mike Frysinger  <vapier@gentoo.org>
 
 	* sim/callback.h (struct host_callback_struct): Change lseek return and

include/sim/callback.h

@@ -91,6 +91,7 @@ struct host_callback_struct
   int (*to_lstat) (host_callback *, const char *, struct stat *);
   int (*ftruncate) (host_callback *, int, int64_t);
   int (*truncate) (host_callback *, const char *, int64_t);
+  int (*getpid) (host_callback *);
   int (*pipe) (host_callback *, int *);
 
   /* Called by the framework when a read call has emptied a pipe buffer.  */

sim/common/ChangeLog

@@ -1,3 +1,9 @@
+2021-06-22  Mike Frysinger  <vapier@gentoo.org>
+
+	* callback.c (os_getpid): New function.
+	(default_callback): Add os_getpid.
+	* syscall.c (cb_syscall): Change getpid to cb->getpid.
+
 2021-06-22  Mike Frysinger  <vapier@gentoo.org>
 
 	* Make-common.in (VPATH): Use $(srcdir).

sim/common/callback.c

@@ -556,6 +556,17 @@ os_truncate (host_callback *p, const char *file, int64_t len)
 #endif
 }
 
+static int
+os_getpid (host_callback *p)
+{
+  int result;
+
+  result = getpid ();
+  /* POSIX says getpid always succeeds.  */
+  p->last_errno = 0;
+  return result;
+}
+
 static int
 os_pipe (host_callback *p, int *filedes)
 {
@@ -737,6 +748,8 @@ host_callback default_callback =
   os_ftruncate,
   os_truncate,
 
+  os_getpid,
+
   os_pipe,
   os_pipe_empty,
   os_pipe_nonempty,

sim/common/syscall.c

@@ -579,7 +579,8 @@ cb_syscall (host_callback *cb, CB_SYSCALL *sc)
       break;
 
     case CB_SYS_getpid:
-      result = getpid ();
+      /* POSIX says getpid always succeeds.  */
+      result = (*cb->getpid) (cb);
       break;
 
     case CB_SYS_time :