Note as explained in [2] we need to use following nop10:
       PF1   PF2   ESC   NOPL  MOD   SIB   DISP32
NOP10: 0x66, 0x2e, 0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00 -- cs nopw 0x00000000(%rax,%rax,1)

which means we need to allow 0x2e prefix which maps to INAT_PFX_CS
attribute in is_prefix_bad function.

This isn't a bug, but could the changelog be updated to describe the
approach actually taken? The patch bypasses uprobe_init_insn() (and
therefore is_prefix_bad()) entirely when can_optimize() is true for the
nop10. The is_prefix_bad() function itself remains unchanged and still
returns true for the CS prefix.

Unoptimize path (int3_update_unoptimize):

  1) Initial optimized state:
      48 8d 64 24 80 e8 d0 d1 d2 d3
     Same as 3) above.

  2) Trap new entries before restoring the NOP bytes:
      [cc] 8d 64 24 80 e8 d0 d1 d2 d3

     From offset 0 this traps. A thread that had already executed the
     LEA can still reach the intact CALL at offset 5.

  3) Restore bytes 1..4 of the original NOP while keeping byte 0 trapped
     and byte 5 as CALL.
      cc [2e 0f 1f 84] e8 d0 d1 d2 d3

     From offset 0 this still traps. Offset 5 is still the CALL for any
     thread that was already past the first LEA byte.

  4) Publish the first byte of the original NOP:
      [66] 2e 0f 1f 84 e8 d0 d1 d2 d3

     From offset 0 this is the restored 10-byte NOP; the CALL opcode and
     displacement are now only NOP operands.  Offset 5 still decodes as
     CALL for a thread that was already there.

     Tthere is only a single target uprobe-trampoline for the given nop10
     instruction address, so the CALL instruction will not be changed across
     unoptimization/optimization cycles.

This isn't a bug, but there's a typo: "Tthere is only a single target"
should be "There is only a single target".


---
AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md

CI run summary: https://github.com/kernel-patches/bpf/actions/runs/28514315910