Re: [PATCH v4 2/4] xen: Add files needed for minimal ppc64le build

[Jan Beulich <jbeulich@xxxxxxxx>]

On 16.06.2023 22:39, Julien Grall wrote:
> On 16/06/2023 21:24, Andrew Cooper wrote:
>>> --- /dev/null
>>> +++ b/xen/arch/ppc/ppc64/head.S
>>> @@ -0,0 +1,27 @@
>>> +/* SPDX-License-Identifier: GPL-2.0-or-later */
>>> +
>>> +.section .text.header, "ax", %progbits
>>> +
>>> +ENTRY(start)
>>> +    /*
>>> +     * Depending on how we were booted, the CPU could be running in either
>>> +     * Little Endian or Big Endian mode. The following trampoline from 
>>> Linux
>>> +     * cleverly uses an instruction that encodes to a NOP if the CPU's
>>> +     * endianness matches the assumption of the assembler (LE, in our case)
>>> +     * or a branch to code that performs the endian switch in the other 
>>> case.
>>> +     */
>>> +    tdi 0, 0, 0x48    /* Reverse endian of b . + 8          */
>>> +    b . + 44          /* Skip trampoline if endian is good  */
>>> +    .long 0xa600607d  /* mfmsr r11                          */
>>> +    .long 0x01006b69  /* xori r11,r11,1                     */
>>> +    .long 0x00004039  /* li r10,0                           */
>>> +    .long 0x6401417d  /* mtmsrd r10,1                       */
>>> +    .long 0x05009f42  /* bcl 20,31,$+4                      */
>>> +    .long 0xa602487d  /* mflr r10                           */
>>> +    .long 0x14004a39  /* addi r10,r10,20                    */
>>> +    .long 0xa6035a7d  /* mtsrr0 r10                         */
>>> +    .long 0xa6037b7d  /* mtsrr1 r11                         */
>>> +    .long 0x2400004c  /* rfid                               */
>>> +
>>> +    /* Now that the endianness is confirmed, continue */
>>> +1:  b 1b
>>
>> .size start, . - start
>> .type start, %function
> 
> Shouldn't we introduce ENDPROC()/END() to avoid open-coding these two 
> lines everywhere?

A proposal for this is pending, see "x86: annotate entry points with
type and size". That proposal extends to asking whether to use this
scheme uniformly, not just for x86.

Jan