> libbpf: Change has_nop_combo to work on top of nop10
>
> We now expect nop combo with 10 bytes nop instead of 5 bytes nop,
> fixing has_nop_combo to reflect that.
>
> Fixes: 41a5c7df4466 ("libbpf: Add support to detect nop,nop5 instructions
> combo for usdt probe")
Should the Fixes tag reference commit 5c3c59c7952a ("uprobes/x86: Move
optimized uprobe from nop5 to nop10") instead? Commit 41a5c7df4466 originally
introduced has_nop_combo() with the correct nop5 check. Commit 5c3c59c7952a
later changed the kernel to use nop10 instead of nop5 for uprobe optimization
but failed to update the libbpf has_nop_combo() function accordingly, creating
a mismatch between kernel and userspace.
> Reviewed-by: Jakub Sitnicki <[email protected]>
> Signed-off-by: Jiri Olsa <[email protected]>
>
> diff --git a/tools/lib/bpf/usdt.c b/tools/lib/bpf/usdt.c
> index e3710933fd52..7e62e4d5bedd 100644
> --- a/tools/lib/bpf/usdt.c
> +++ b/tools/lib/bpf/usdt.c
[ ... ]
> @@ -596,14 +596,14 @@ static int parse_usdt_spec(struct usdt_spec *spec,
> const struct usdt_note *note,
> #if defined(__x86_64__)
> static bool has_nop_combo(int fd, long off)
> {
> - unsigned char nop_combo[6] = {
> - 0x90, 0x0f, 0x1f, 0x44, 0x00, 0x00 /* nop,nop5 */
> + unsigned char nop_combo[11] = {
> + 0x90, 0x66, 0x66, 0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00,
> 0x00,
> };
> - unsigned char buf[6];
> + unsigned char buf[11];
>
> - if (pread(fd, buf, 6, off) != 6)
> + if (pread(fd, buf, 11, off) != 11)
> return false;
> - return memcmp(buf, nop_combo, 6) == 0;
> + return memcmp(buf, nop_combo, 11) == 0;
> }
This isn't a bug, but Jakub Sitnicki suggested in v1 review to use
ARRAY_SIZE(buf) instead of repeating the scalar value 11 in multiple places.
The suggestion was included alongside the Reviewed-by tag but was not
addressed.
Reference: https://lore.kernel.org/bpf/[email protected]/
[ ... ]
---
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/26030080109
