[U-Boot] instruction "xchgb" for x86_64

[James Wang]

> 
> Hi,
> 
> (James please can you use plain-text email for the mailing list?)
  
OK. Thanks Simon for pointing out this. I am using outlook, so most likely will have "newline" difference. Hope can find a way out for this.
 
> 
> For chromebook_link64 I get:
> 
> output: '/usr/local/google/home/sjg/cosarm/src/third_party/u-
> boot/files/arch/x86/include/asm/byteorder.h:
> Assembler messages:
> /usr/local/google/home/sjg/cosarm/src/third_party/u-
> boot/files/arch/x86/include/asm/byteorder.h:22:
> Error: register type mismatch for `xchg'
> make[2]: *** [/usr/local/google/home/sjg/cosarm/src/third_party/u-
> boot/files/scripts/Makefile.build:278:
> net/tftp.o] Error 1
> make[2]: *** Waiting for unfinished jobs....
> /usr/local/google/home/sjg/cosarm/src/third_party/u-boot/files/net/net.c:
> In function 'net_process_received_packet':
> /usr/local/google/home/sjg/cosarm/src/third_party/u-
> boot/files/net/net.c:1324:1:
> error: extended registers have no high halves  }  ^
> /usr/local/google/home/sjg/cosarm/src/third_party/u-
> boot/files/arch/x86/include/asm/byteorder.h:
> Assembler messages:
> /usr/local/google/home/sjg/cosarm/src/third_party/u-
> boot/files/arch/x86/include/asm/byteorder.h:22:
> Error: register type mismatch for `xchg'
> /usr/local/google/home/sjg/cosarm/src/third_party/u-
> boot/files/arch/x86/include/asm/byteorder.h:22:
> Error: register type mismatch for `xchg'
> /usr/local/google/home/sjg/cosarm/src/third_party/u-
> boot/files/arch/x86/include/asm/byteorder.h:22:
> Error: register type mismatch for `xchg'
> make[2]: *** [/usr/local/google/home/sjg/cosarm/src/third_party/u-
> boot/files/scripts/Makefile.build:278:
> net/net.o] Error 1
> make[1]: *** [/usr/local/google/home/sjg/cosarm/src/third_party/u-
> boot/files/Makefile:1588:
> net] Error 2
> make[1]: *** Waiting for unfinished jobs....
> make: *** [Makefile:148: sub-make] Error 2
> 
> Perhaps there is another way to fix this?
> 

I tested two toolchains: 
1. With gcc version 7.3-win32 20180312 (the MinGW-w64 cross compiling), it can assemble the xchgb without error.
2. With gcc version 7.3.0 (Ubuntu 7.3.0-27ubuntu1~18.04), it uses /usr/include/x86_64-linux-gnu/asm/byteorder.h, (not the one in uboot), and that file is only to include the <little_endian.h> file

As the assembler you use reports error for xchgb  (no matter what's the cause), we may use ONLY the C version of implementation and remove the assembly version and relevant  CONFIG_IS_ENABLED checking (if performance is not critical here)?

How do you think, Simon and Bin?

Best regards
James Wang Jinmin