[U-Boot] instruction "xchgb" for x86_64
James.Wang at rohde-schwarz.com
Wed Aug 14 05:08:49 UTC 2019
This is James and am working on u-boot to bring back MinGW tool chain for cross compiling host tools for Windows on Linux. After complete the code, I plan to generate a patch for community review.
During work, I face an compiling error in file <arch/x86/include/asm/byteorder.h> with macro CONFIG_IS_ENABLED. After some background study, seems this macro should not be available when compiling host tools.
After check history, it's from 909780506773a9b09ae88cb267dbfa6a8d0caa7b on 2017-01-16 22:04:04, Below is the log message
x86: Fix up byteorder.h for x86_64
Remove the very old x86 code and add support for 64-bit.
Signed-off-by: Simon Glass <sjg at chromium.org<mailto:sjg at chromium.org>>
Reviewed-by: Bin Meng bmeng.cn at gmail.com<mailto:bmeng.cn at gmail.com>
Below are the relevant changes.
+#define _constant_swab16(x) ((__u16)( \
+ (((__u16)(x) & (__u16)0x00ffU) << 8) | \
+ (((__u16)(x) & (__u16)0xff00U) >> 8)))
static __inline__ __u16 ___arch__swab16(__u16 x)
+ return _constant_swab16(x);
__asm__("xchgb %b0,%h0" /* swap bytes */ \
: "=q" (x) \
: "0" (x)); \
I am not familiar with x86 instructions and not understand the purpose of this change, is it because instruction "xchgb" not available on 64-bit architecture or something else?
James Wang Jinmin
Rohde & Schwarz Asia Pte Ltd
9 Changi Business Park Vista, #01-01, Singapore 486 041
DID: 65-6307 0374 Fax: 65-6307 0300
[ONE logo 2018_email]
Privileged/Confidential information may be contained in this message.
If you are not the intended recipient, Please notify the sender immediately and
you must not use the message for any purpose nor disclose it to anyone.
P Please consider the environment before printing this email. <http://www.rohde-schwarz.com.sg/>
-------------- next part --------------
A non-text attachment was scrubbed...
Size: 13947 bytes
More information about the U-Boot