Re: [Tinycc-devel] [PATCH 2/2] x86_64-asm: support endbr64 instruction

[grischka]

On 29.09.2024 09:58, Yao Zi via Tinycc-devel wrote:
> endbr64 has no operand but comes with a ModR/M byte. Handle it in the
> same way as *fence instructions.

If you know what you're doing then please push
-> https://repo.or.cz/w/tinycc.git

Thanks, -- gr


> Signed-off-by: Yao Zi <ziyao@disroot.org>
> ---
>   i386-asm.c   | 12 +++++++++---
>   x86_64-asm.h |  3 +++
>   2 files changed, 12 insertions(+), 3 deletions(-)
>
> diff --git a/i386-asm.c b/i386-asm.c
> index 33783d5f..a3e16fb8 100644
> --- a/i386-asm.c
> +++ b/i386-asm.c
> @@ -1002,15 +1002,21 @@ again:
>       modrm_index = -1;
>       modreg_index = -1;
>       if (pa->instr_type & OPC_MODRM) {
> +#ifdef TCC_TARGET_X86_64
>         if (!nb_ops) {
>             /* A modrm opcode without operands is a special case (e.g. mfence).
> -              It has a group and acts as if there's an register operand 0
> -              (ax).  */
> +              It has a group and acts as if there's an register operand */
>             i = 0;
>             ops[i].type = OP_REG;
> -           ops[i].reg = 0;
> +           if (pa->sym == TOK_ASM_endbr64)
> +             ops[i].reg = 2; // dx
> +           else if (pa->sym >= TOK_ASM_lfence && pa->sym <= TOK_ASM_sfence)
> +             ops[i].reg = 0; // ax
> +           else
> +             tcc_error("bad MODR/M opcode without operands");
>             goto modrm_found;
>         }
> +#endif
>           /* first look for an ea operand */
>           for(i = 0;i < nb_ops; i++) {
>               if (op_type[i] & OP_EA)
> diff --git a/x86_64-asm.h b/x86_64-asm.h
> index e4655a7a..883232ea 100644
> --- a/x86_64-asm.h
> +++ b/x86_64-asm.h
> @@ -538,6 +538,9 @@ ALT(DEF_ASM_OP2(movhps, 0x0f17, 0, OPC_MODRM, OPT_SSE, 
> OPT_EA | OPT_REG32 ))
>       DEF_ASM_OP0L(mfence, 0x0fae, 6, OPC_MODRM)
>       DEF_ASM_OP0L(sfence, 0x0fae, 7, OPC_MODRM)
>       DEF_ASM_OP1(clflush, 0x0fae, 7, OPC_MODRM, OPT_EA)
> +
> +    /* Control-Flow Enforcement */
> +    DEF_ASM_OP0L(endbr64, 0xf30f1e, 7, OPC_MODRM)
>   #undef ALT
>   #undef DEF_ASM_OP0
>   #undef DEF_ASM_OP0L