On Mon, Jul 14, 2025 at 11:48:24AM +0200, Peter Zijlstra wrote:
> On Fri, Jul 11, 2025 at 10:29:18AM +0200, Jiri Olsa wrote:
> > +enum {
> > + OPT_PART,
> > + OPT_INSN,
> > + UNOPT_INT3,
> > + UNOPT_PART,
> > +};
> > +
> > +struct write_opcode_ctx {
> > + unsigned long base;
> > + int update;
> > +};
> > +
> > +static int is_call_insn(uprobe_opcode_t *insn)
> > +{
> > + return *insn == CALL_INSN_OPCODE;
> > +}
> > +
> > +static int verify_insn(struct page *page, unsigned long vaddr, uprobe_opcode_t *new_opcode,
> > + int nbytes, void *data)
> > +{
> > + struct write_opcode_ctx *ctx = data;
> > + uprobe_opcode_t old_opcode[5];
> > +
> > + uprobe_copy_from_page(page, ctx->base, (uprobe_opcode_t *) &old_opcode, 5);
> > +
> > + switch (ctx->update) {
> > + case OPT_PART:
> > + case OPT_INSN:
> > + if (is_swbp_insn(&old_opcode[0]))
> > + return 1;
> > + break;
> > + case UNOPT_INT3:
> > + if (is_call_insn(&old_opcode[0]))
> > + return 1;
> > + break;
> > + case UNOPT_PART:
> > + if (is_swbp_insn(&old_opcode[0]))
> > + return 1;
> > + break;
> > + }
> > +
> > + return -1;
> > +}
> > +
> > +static int write_insn(struct arch_uprobe *auprobe, struct vm_area_struct *vma, unsigned long vaddr,
> > + uprobe_opcode_t *insn, int nbytes, void *ctx)
> > +{
> > + return uprobe_write(auprobe, vma, vaddr, insn, nbytes, verify_insn,
> > + true /* is_register */, false /* do_update_ref_ctr */, ctx);
> > +}
> > +
> > +static void relative_call(void *dest, long from, long to)
> > +{
> > + struct __packed __arch_relative_insn {
> > + u8 op;
> > + s32 raddr;
> > + } *insn;
> > +
> > + insn = (struct __arch_relative_insn *)dest;
> > + insn->raddr = (s32)(to - (from + 5));
> > + insn->op = CALL_INSN_OPCODE;
> > +}
>
> We already have this in asm/text-patching.h, its called
> __text_gen_insn().
>
> > +
> > +static int swbp_optimize(struct arch_uprobe *auprobe, struct vm_area_struct *vma,
> > + unsigned long vaddr, unsigned long tramp)
> > +{
> > + struct write_opcode_ctx ctx = {
> > + .base = vaddr,
> > + };
> > + char call[5];
> > + int err;
> > +
> > + relative_call(call, vaddr, tramp);
>
> __text_gen_insn(call, CALL_INSN_OPCODE, vaddr, tramp, CALL_INSN_SIZE);
ok, will use that
>
> > +
> > + /*
> > + * We are in state where breakpoint (int3) is installed on top of first
> > + * byte of the nop5 instruction. We will do following steps to overwrite
> > + * this to call instruction:
> > + *
> > + * - sync cores
> > + * - write last 4 bytes of the call instruction
> > + * - sync cores
> > + * - update the call instruction opcode
>
> The sanctioned text poke sequence has another sync-core at the end.
> Please also do this.
ok
>
> > + */
> > +
> > + smp_text_poke_sync_each_cpu();
> > +
> > + ctx.update = OPT_PART;
> > + err = write_insn(auprobe, vma, vaddr + 1, call + 1, 4, &ctx);
> > + if (err)
> > + return err;
> > +
> > + smp_text_poke_sync_each_cpu();
> > +
> > + ctx.update = OPT_INSN;
> > + return write_insn(auprobe, vma, vaddr, call, 1, &ctx);
> > +}
> > +
> > +static int swbp_unoptimize(struct arch_uprobe *auprobe, struct vm_area_struct *vma,
> > + unsigned long vaddr)
> > +{
> > + uprobe_opcode_t int3 = UPROBE_SWBP_INSN;
> > + struct write_opcode_ctx ctx = {
> > + .base = vaddr,
> > + };
> > + int err;
> > +
> > + /*
> > + * We need to overwrite call instruction into nop5 instruction with
> > + * breakpoint (int3) installed on top of its first byte. We will:
> > + *
> > + * - overwrite call opcode with breakpoint (int3)
> > + * - sync cores
> > + * - write last 4 bytes of the nop5 instruction
> > + * - sync cores
> > + */
> > +
> > + ctx.update = UNOPT_INT3;
> > + err = write_insn(auprobe, vma, vaddr, &int3, 1, &ctx);
> > + if (err)
> > + return err;
> > +
> > + smp_text_poke_sync_each_cpu();
> > +
> > + ctx.update = UNOPT_PART;
> > + err = write_insn(auprobe, vma, vaddr + 1, (uprobe_opcode_t *) auprobe->insn + 1, 4, &ctx);
> > +
> > + smp_text_poke_sync_each_cpu();
> > + return err;
> > +}
>
> Please unify these two functions; it makes absolutely no sense to have
> two copies of this logic around.
will try to come up with something
thanks,
jirka
