arm: smh: Return errno on error

Instead of printing in what are now library functions, try to return a
numeric error code. This also adjust some functions (such as read) to
behave more similarly to read(2). For example, we now return the number
of bytes read instead of failing immediately on a short read.
Signed-off-by: NSean Anderson <sean.anderson@seco.com>

arch/arm/lib/semihosting.c

@@ -21,6 +21,7 @@
 #define SYSCLOSE	0x02
 #define SYSREAD		0x06
 #define SYSFLEN		0x0C
+#define SYSERRNO	0x13
 
 /*
  * Call the handler
@@ -39,10 +40,24 @@ static noinline long smh_trap(unsigned int sysnum, void *addr)
 	return result;
 }
 
-/*
- * Open a file on the host. Mode is "r" or "rb" currently. Returns a file
- * descriptor or -1 on error.
+/**
+ * smh_errno() - Read the host's errno
+ *
+ * This gets the value of the host's errno and negates it. The host's errno may
+ * or may not be set, so only call this function if a previous semihosting call
+ * has failed.
+ *
+ * Return: a negative error value
  */
+static int smh_errno(void)
+{
+	long ret = smh_trap(SYSERRNO, NULL);
+
+	if (ret > 0 && ret < INT_MAX)
+		return -ret;
+	return -EIO;
+}
+
 long smh_open(const char *fname, enum smh_open_mode mode)
 {
 	long fd;
@@ -61,9 +76,7 @@ long smh_open(const char *fname, enum smh_open_mode mode)
 	/* Open the file on the host */
 	fd = smh_trap(SYSOPEN, &open);
 	if (fd == -1)
-		printf("%s: ERROR fd %ld for file \'%s\'\n", __func__, fd,
-		       fname);
-
+		return smh_errno();
 	return fd;
 }
 
@@ -86,19 +99,9 @@ long smh_read(long fd, void *memp, size_t len)
 	read.len = len;
 
 	ret = smh_trap(SYSREAD, &read);
-	if (ret < 0) {
-		/*
-		 * The ARM handler allows for returning partial lengths,
-		 * but in practice this never happens so rather than create
-		 * hard to maintain partial read loops and such, just fail
-		 * with an error message.
-		 */
-		printf("%s: ERROR ret %ld, fd %ld, len %zu memp %p\n",
-		       __func__, ret, fd, len, memp);
-		return -1;
-	}
-
-	return 0;
+	if (ret < 0)
+		return smh_errno();
+	return len - ret;
 }
 
 /*
@@ -112,9 +115,8 @@ long smh_close(long fd)
 
 	ret = smh_trap(SYSCLOSE, &fd);
 	if (ret == -1)
-		printf("%s: ERROR fd %ld\n", __func__, fd);
-
-	return ret;
+		return smh_errno();
+	return 0;
 }
 
 /*
@@ -128,8 +130,7 @@ long smh_flen(long fd)
 
 	ret = smh_trap(SYSFLEN, &fd);
 	if (ret == -1)
-		printf("%s: ERROR ret %ld, fd %ld\n", __func__, ret, fd);
-
+		return smh_errno();
 	return ret;
 }
 
@@ -141,28 +142,32 @@ static int smh_load_file(const char * const name, ulong load_addr,
 	long ret;
 
 	fd = smh_open(name, MODE_READ | MODE_BINARY);
-	if (fd == -1)
-		return -1;
+	if (fd < 0)
+		return fd;
 
 	len = smh_flen(fd);
 	if (len < 0) {
 		smh_close(fd);
-		return -1;
+		return len;
 	}
 
 	ret = smh_read(fd, (void *)load_addr, len);
 	smh_close(fd);
 
-	if (ret == 0) {
+	if (ret == len) {
 		*end_addr = load_addr + len - 1;
 		printf("loaded file %s from %08lX to %08lX, %08lX bytes\n",
 		       name,
 		       load_addr,
 		       *end_addr,
 		       len);
-	} else {
-		printf("read failed\n");
-		return 0;
+	} else if (ret >= 0) {
+		ret = -EAGAIN;
+	}
+
+	if (ret < 0) {
+		printf("read failed: %ld\n", ret);
+		return ret;
 	}
 
 	return 0;