Re: [PATCH v2] Reduce assembly code size of exception entry points

[Jan Beulich <jbeulich@xxxxxxxx>]

On 14.02.2024 11:35, Frediano Ziglio wrote:
> We just pushed a 8-bytes zero

This part is now somewhat stale.

> and exception constants are
> small so we can just write a single byte saving 3 bytes for
> instruction.
> With ENDBR64 this reduces the size of many entry points from 32 to
> 16 bytes (due to alignment).
> Similar code is already used in autogen_stubs.
> 
> Signed-off-by: Frediano Ziglio <frediano.ziglio@xxxxxxxxx>
> --
> v2:
> - added missing entry points;

What about entry_int82?

> @@ -653,7 +653,7 @@ END(ret_from_intr)
>          .section .init.text, "ax", @progbits
>  FUNC(early_page_fault)
>          ENDBR64
> -        movl  $X86_EXC_PF, 4(%rsp)
> +        movb  $X86_EXC_PF, 4(%rsp)
>          SAVE_ALL
>          movq  %rsp, %rdi
>          call  do_early_page_fault

Between this and the next hunk there's also entry_PF.

Jan

> @@ -898,105 +898,105 @@ END(handle_exception)
>  FUNC(entry_DE)
>          ENDBR64
>          pushq $0
> -        movl  $X86_EXC_DE, 4(%rsp)
> +        movb  $X86_EXC_DE, 4(%rsp)
>          jmp   handle_exception
>  END(entry_DE)
>  
>  FUNC(entry_MF)
>          ENDBR64
>          pushq $0
> -        movl  $X86_EXC_MF, 4(%rsp)
> +        movb  $X86_EXC_MF, 4(%rsp)
>          jmp   handle_exception
>  END(entry_MF)
>  
>  FUNC(entry_XM)
>          ENDBR64
>          pushq $0
> -        movl  $X86_EXC_XM, 4(%rsp)
> +        movb  $X86_EXC_XM, 4(%rsp)
>          jmp   handle_exception
>  END(entry_XM)
>  
>  FUNC(entry_NM)
>          ENDBR64
>          pushq $0
> -        movl  $X86_EXC_NM, 4(%rsp)
> +        movb  $X86_EXC_NM, 4(%rsp)
>          jmp   handle_exception
>  END(entry_NM)
>  
>  FUNC(entry_DB)
>          ENDBR64
>          pushq $0
> -        movl  $X86_EXC_DB, 4(%rsp)
> +        movb  $X86_EXC_DB, 4(%rsp)
>          jmp   handle_ist_exception
>  END(entry_DB)
>  
>  FUNC(entry_BP)
>          ENDBR64
>          pushq $0
> -        movl  $X86_EXC_BP, 4(%rsp)
> +        movb  $X86_EXC_BP, 4(%rsp)
>          jmp   handle_exception
>  END(entry_BP)
>  
>  FUNC(entry_OF)
>          ENDBR64
>          pushq $0
> -        movl  $X86_EXC_OF, 4(%rsp)
> +        movb  $X86_EXC_OF, 4(%rsp)
>          jmp   handle_exception
>  END(entry_OF)
>  
>  FUNC(entry_BR)
>          ENDBR64
>          pushq $0
> -        movl  $X86_EXC_BR, 4(%rsp)
> +        movb  $X86_EXC_BR, 4(%rsp)
>          jmp   handle_exception
>  END(entry_BR)
>  
>  FUNC(entry_UD)
>          ENDBR64
>          pushq $0
> -        movl  $X86_EXC_UD, 4(%rsp)
> +        movb  $X86_EXC_UD, 4(%rsp)
>          jmp   handle_exception
>  END(entry_UD)
>  
>  FUNC(entry_TS)
>          ENDBR64
> -        movl  $X86_EXC_TS, 4(%rsp)
> +        movb  $X86_EXC_TS, 4(%rsp)
>          jmp   handle_exception
>  END(entry_TS)
>  
>  FUNC(entry_NP)
>          ENDBR64
> -        movl  $X86_EXC_NP, 4(%rsp)
> +        movb  $X86_EXC_NP, 4(%rsp)
>          jmp   handle_exception
>  END(entry_NP)
>  
>  FUNC(entry_SS)
>          ENDBR64
> -        movl  $X86_EXC_SS, 4(%rsp)
> +        movb  $X86_EXC_SS, 4(%rsp)
>          jmp   handle_exception
>  END(entry_SS)
>  
>  FUNC(entry_GP)
>          ENDBR64
> -        movl  $X86_EXC_GP, 4(%rsp)
> +        movb  $X86_EXC_GP, 4(%rsp)
>          jmp   handle_exception
>  END(entry_GP)
>  
>  FUNC(entry_AC)
>          ENDBR64
> -        movl  $X86_EXC_AC, 4(%rsp)
> +        movb  $X86_EXC_AC, 4(%rsp)
>          jmp   handle_exception
>  END(entry_AC)
>  
>  FUNC(entry_CP)
>          ENDBR64
> -        movl  $X86_EXC_CP, 4(%rsp)
> +        movb  $X86_EXC_CP, 4(%rsp)
>          jmp   handle_exception
>  END(entry_CP)
>  
>  FUNC(entry_DF)
>          ENDBR64
> -        movl  $X86_EXC_DF, 4(%rsp)
> +        movb  $X86_EXC_DF, 4(%rsp)
>          /* Set AC to reduce chance of further SMAP faults */
>          ALTERNATIVE "", stac, X86_FEATURE_XEN_SMAP
>          SAVE_ALL
> @@ -1022,7 +1022,7 @@ END(entry_DF)
>  FUNC(entry_NMI)
>          ENDBR64
>          pushq $0
> -        movl  $X86_EXC_NMI, 4(%rsp)
> +        movb  $X86_EXC_NMI, 4(%rsp)
>  END(entry_NMI)
>  
>  FUNC(handle_ist_exception)
> @@ -1158,7 +1158,7 @@ END(handle_ist_exception)
>  FUNC(entry_MC)
>          ENDBR64
>          pushq $0
> -        movl  $X86_EXC_MC, 4(%rsp)
> +        movb  $X86_EXC_MC, 4(%rsp)
>          jmp   handle_ist_exception
>  END(entry_MC)
>