Re: [PATCH 2/3] LoongArch: Add prologue unwinder support

[zhangqing]

On 2022/7/29 上午10:03, Youling Tang wrote:
> On 07/28/2022 10:05 PM, Qing Zhang wrote:
> > It unwind the stack frame based on prologue code analyze.
> > CONFIG_KALLSYMS is needed, at least the address and length
> > of each function.
> >
> > Three stages when we do unwind,
> >   (1)unwind_start(), the prapare of unwinding, fill unwind_state.
> >   (2)unwind_done(), judge whether the unwind process is finished or not.
> >   (3)unwind_next_frame(), unwind the next frame.
> >
> > Dividing unwinder helps to add new unwinders in the future, eg:
> > unwind_frame, unwind_orc .etc
> >
> > Signed-off-by: Qing Zhang <zhangqing@xxxxxxxxxxx>
> >
> > +
> > +    while (ip < ip_end) {
> > +        if (is_ra_save_ins(ip)) {
> > +            frame_ra = ip->reg2i12_format.immediate;
> Because the immediate member in struct reg2i12_format is defined as an
> unsigned type, the value obtained by frame_ra here can only be a
> positive number.
>
> > +            break;
> > +        }
> > +        if (is_branch_insn(*ip))
> > +            break;
> > +        ip++;
> > +    }
> > +
> > +    if (frame_ra < 0) {
> In addition to judging whether the initial value of frame_ra is
> negative, we also want to judge whether the previously assigned
> frame_ra is negative.
>
> Save the ra value to the stack in the prologue, offset must be a
> positive number, so we can add another judgment to is_ra_save_ins, the
> code is as follows:
> +static inline bool is_ra_save_ins(union loongarch_instruction *ip)
> +{
> +    /* st.d $ra, $sp, offset */
> +    return ip->reg2i12_format.opcode == std_op &&
> +        ip->reg2i12_format.rj == LOONGARCH_GPR_SP &&
> +        ip->reg2i12_format.rd == LOONGARCH_GPR_RA &&
> +        !(ip->reg2i12_format.immediate & (1 << 11));
> +}

Hi,
youling

you are right and I will send v2.

Thanks,
Qing