Re: [PATCH v3 12/22] x86/traps: Introduce FRED entrypoints

[Jan Beulich <jbeulich@xxxxxxxx>]

On 04.10.2025 00:53, Andrew Cooper wrote:
> --- a/xen/arch/x86/include/asm/asm_defns.h
> +++ b/xen/arch/x86/include/asm/asm_defns.h
> @@ -315,6 +315,71 @@ static always_inline void stac(void)
>          subq  $-(UREGS_error_code-UREGS_r15+\adj), %rsp
>  .endm
>  
> +/*
> + * Push and clear GPRs
> + */
> +.macro PUSH_AND_CLEAR_GPRS
> +        push  %rdi
> +        xor   %edi, %edi
> +        push  %rsi
> +        xor   %esi, %esi
> +        push  %rdx
> +        xor   %edx, %edx
> +        push  %rcx
> +        xor   %ecx, %ecx
> +        push  %rax
> +        xor   %eax, %eax
> +        push  %r8
> +        xor   %r8d, %r8d
> +        push  %r9
> +        xor   %r9d, %r9d
> +        push  %r10
> +        xor   %r10d, %r10d
> +        push  %r11
> +        xor   %r11d, %r11d
> +        push  %rbx
> +        xor   %ebx, %ebx
> +        push  %rbp
> +#ifdef CONFIG_FRAME_POINTER
> +/* Indicate special exception stack frame by inverting the frame pointer. */
> +        mov   %rsp, %rbp
> +        notq  %rbp
> +#else
> +        xor   %ebp, %ebp
> +#endif
> +        push  %r12
> +        xor   %r12d, %r12d
> +        push  %r13
> +        xor   %r13d, %r13d
> +        push  %r14
> +        xor   %r14d, %r14d
> +        push  %r15
> +        xor   %r15d, %r15d
> +.endm
> +
> +/*
> + * POP GPRs from a UREGS_* frame on the stack.  Does not modify flags.
> + *
> + * @rax: Alternative destination for the %rax value on the stack.
> + */
> +.macro POP_GPRS rax=%rax
> +        pop   %r15
> +        pop   %r14
> +        pop   %r13
> +        pop   %r12
> +        pop   %rbp
> +        pop   %rbx
> +        pop   %r11
> +        pop   %r10
> +        pop   %r9
> +        pop   %r8
> +        pop   \rax

For placing the entry_ssp field I came back looking here. I notice there
was a v2 comment regarding the rax macro parameter. Besides there being
a limitation on which registers may be used, a %rsp-relative memory
operand can't be (cleanly) used either. I think if you really want to
retain that parameter, some warning needs adding to the comment.

Jan