[PATCH v7 13/15] lib/bootconfig: use signed type for offset in xbc_init_node()

[Josh Law <objecting@objecting.org>]

  lib/bootconfig.c:415:32: warning: conversion to 'long unsigned int'
  from 'long int' may change the sign of the result [-Wsign-conversion]

Pointer subtraction yields ptrdiff_t (signed), which was stored in
unsigned long.  The original unsigned type implicitly caught a negative
offset (data < xbc_data) because the wrapped value would exceed
XBC_DATA_MAX.  Make this intent explicit by using a signed long and
adding an offset < 0 check to the WARN_ON condition.

Signed-off-by: Josh Law <objecting@objecting.org>
---
 lib/bootconfig.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/lib/bootconfig.c b/lib/bootconfig.c
index 3c5b6ad32a54..119c3d429c1f 100644
--- a/lib/bootconfig.c
+++ b/lib/bootconfig.c
@@ -412,9 +412,9 @@ const char * __init xbc_node_find_next_key_value(struct xbc_node *root,
 
 static int __init xbc_init_node(struct xbc_node *node, char *data, uint16_t flag)
 {
-	unsigned long offset = data - xbc_data;
+	long offset = data - xbc_data;
 
-	if (WARN_ON(offset >= XBC_DATA_MAX))
+	if (WARN_ON(offset < 0 || offset >= XBC_DATA_MAX))
 		return -EINVAL;
 
 	node->data = (uint16_t)offset | flag;
-- 
2.34.1