kernel: fix case of EAX getting clobbered after sigreturn.

kernel/arch/i386/memory.c

@@ -612,7 +612,9 @@ PUBLIC void delivermsg(struct proc *rp)
 		r = OK;
 	}
 
-	rp->p_reg.retreg = r;
+	if(!(rp->p_misc_flags & MF_CONTEXT_SET)) {
+		rp->p_reg.retreg = r;
+	}
 }
 
 PRIVATE char *flagstr(u32_t e, const int dir)

kernel/proc.h

@@ -224,6 +224,7 @@ struct proc {
 #define MF_FPU_INITIALIZED	0x1000  /* process already used math, so fpu
 					 * regs are significant (initialized)*/
 #define MF_SENDING_FROM_KERNEL	0x2000 /* message of this process is from kernel */
+#define MF_CONTEXT_SET	0x4000 /* don't touch context */
 
 /* Magic process table addresses. */
 #define BEG_PROC_ADDR (&proc[0])

kernel/system/do_sigreturn.c

@@ -65,6 +65,8 @@ PUBLIC int do_sigreturn(struct proc * caller, message * m_ptr)
   }
 #endif
 
+  rp->p_misc_flags |= MF_CONTEXT_SET;
+
   return(OK);
 }
 #endif /* USE_SIGRETURN */