[PATCH] x86/bitmap: Compile with -Wsign-conversion

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

Use pragmas to able the warning in this file only.  All supported versions of
Clang understand this, while older GCCs simply ignore it.

bitmap_find_free_region() is the only function which isn't sign-convert
clean.  This highlights a latent bug in that it can't return successfully for
a bitmap larger than 2G.

Add an extra check, and explicit cast to silence the warning.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: George Dunlap <George.Dunlap@xxxxxxxxxx>
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Stefano Stabellini <sstabellini@xxxxxxxxxx>
CC: Wei Liu <wl@xxxxxxx>
CC: Julien Grall <julien@xxxxxxx>

Slightly RFC.  This is our first use of pragmas like this.
---
 xen/common/bitmap.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/xen/common/bitmap.c b/xen/common/bitmap.c
index 18e23e2f0e18..b14f8a3b3030 100644
--- a/xen/common/bitmap.c
+++ b/xen/common/bitmap.c
@@ -14,6 +14,9 @@
 #include <xen/lib.h>
 #include <asm/byteorder.h>
 
+#pragma GCC diagnostic warning "-Wsign-conversion"
+#pragma clang diagnostic warning "-Wsign-conversion"
+
 /*
  * bitmaps provide an array of bits, implemented using an an
  * array of unsigned longs.  The number of valid bits in a
@@ -263,7 +266,7 @@ int bitmap_find_free_region(unsigned long *bitmap, unsigned 
int bits, unsigned i
        unsigned int pages = 1 << order;
        unsigned int i;
 
-       if(pages > BITS_PER_LONG)
+       if (pages > BITS_PER_LONG || bits >= INT_MAX)
                return -EINVAL;
 
        /* make a mask of the order */
@@ -278,7 +281,7 @@ int bitmap_find_free_region(unsigned long *bitmap, unsigned 
int bits, unsigned i
                if((bitmap[index] & (mask << offset)) == 0) {
                        /* set region in bimap */
                        bitmap[index] |= (mask << offset);
-                       return i;
+                       return (int)i;
                }
        }
        return -ENOMEM;
-- 
2.30.2