Subject: Re: [PATCH v3 4/6] xen: Switch to byteswap
On 10/05/2022 11:15, Lin Liu wrote:
Update to use byteswap to swap bytes.
No functional change.
Signed-off-by: Lin Liu <lin.liu@xxxxxxxxxx>
---
Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
Cc: Julien Grall <julien@xxxxxxx>
Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Cc: George Dunlap <george.dunlap@xxxxxxxxxx>
Cc: Jan Beulich <jbeulich@xxxxxxxx>
Cc: Wei Liu <wl@xxxxxxx>
Changes in v3:
- Update xen/common/device_tree.c to use be32_to_cpu
- Keep const in type cast in unaligned.h
---
xen/common/device_tree.c | 44 +++++++++++++++---------------
xen/common/libelf/libelf-private.h | 6 ++--
xen/common/xz/private.h | 2 +-
xen/include/xen/unaligned.h | 24 ++++++++--------
4 files changed, 38 insertions(+), 38 deletions(-)
diff --git a/xen/common/device_tree.c b/xen/common/device_tree.c
index 4aae281e89..70d3be3be6 100644
--- a/xen/common/device_tree.c
+++ b/xen/common/device_tree.c
@@ -171,7 +171,7 @@ bool_t dt_property_read_u32(const struct dt_device_node *np,
if ( !val || len < sizeof(*out_value) )
return 0;
- *out_value = be32_to_cpup(val);
+ *out_value = be32_to_cpu(*val);
This code has been taken from Linux and I would rather prefer to keep
the *cpup* helpers to avoid any changes when backporting.
diff --git a/xen/include/xen/unaligned.h b/xen/include/xen/unaligned.h
index 0a2b16d05d..16b2e6f5f0 100644
--- a/xen/include/xen/unaligned.h
+++ b/xen/include/xen/unaligned.h
@@ -20,62 +20,62 @@
static inline uint16_t get_unaligned_be16(const void *p)
{
- return be16_to_cpup(p);
+ return be16_to_cpu(*(const uint16_t *)p)
I haven't checked the existing implementation of be16_to_cpup().
However, this new approach would allow the compiler to use a single load
instruction to read the 16-bit value from memory. So this change may
break on platform where unaligned access is forbidden (such as arm32).
}
static inline void put_unaligned_be16(uint16_t val, void *p)
{
- *(__force __be16*)p = cpu_to_be16(val);
+ *(__be16 *)p = cpu_to_be16(val);
Why did you drop the __force?
Google told me __force is used in linux kernel to suppress warning in sparse,
https://stackoverflow.com/questions/53120610/what-does-the-attribute-force-do
Is sparse also used in xen?
