Re: [PATCH v3 4/6] LoongArch: Add uprobes support

[Tiezhu Yang]

On 04/23/2023 09:12 PM, Huacai Chen wrote:
> Hi, Tiezhu,
>
> On Wed, Apr 19, 2023 at 5:57 PM Tiezhu Yang <yangtiezhu@xxxxxxxxxxx> wrote:
> > Uprobes is the user-space counterpart to kprobes, this commit
> > adds uprobes support for LoongArch.

...

> > +#define MAX_UINSN_BYTES                8
> > +#define UPROBE_XOL_SLOT_BYTES  MAX_UINSN_BYTES
> In old versions we define UPROBE_XOL_SLOT_BYTES to 128, why we use 8 now?

I assume "the old version" maybe comes from mips, I am not quite sure 
the backgrounds. For LoongArch, there are 2 xol slots to save 2 
instructions, each of them is 32 bit, 2*32bit=8bytes, so 
UPROBE_XOL_SLOT_BYTES can be 8.

> > +
> > +#define UPROBE_XOLBP_INSN      larch_insn_gen_break(BRK_UPROBE_XOLBP)
> > +#define UPROBE_SWBP_INSN       larch_insn_gen_break(BRK_UPROBE_BP)
> > +#define UPROBE_SWBP_INSN_SIZE  LOONGARCH_INSN_SIZE

...

> >         case BRK_UPROBE_XOLBP:
> > -               if (notify_die(DIE_UPROBE_XOL, "Uprobe_XOL", regs, bcode,
> > -                              current->thread.trap_nr, SIGTRAP) == NOTIFY_STOP)
> > +               if (uprobe_singlestep_handler(regs))
> As I know, XOL means "execute out of line", is it an alias of "single step"?

I think so, the instruction filled in xol slots is to single step, 
arm64, riscv, csky also uses "single step" for the related code, 
powerpc, s390 uses "DIE_SSTEP".

Thanks,
Tiezhu