On Mon, 16 Feb 2026 17:30:34 +0100
"Matthieu Baerts (NGI0)" <[email protected]> wrote:
> The verification signature header generation requires converting a
> binary certificate to a C array. Previously this only worked with xxd,
> and a switch to hexdump has been done in commit b640d556a2b3
> ("selftests/bpf: Remove xxd util dependency").
>
> hexdump is a more common utility program, yet it might not be installed
> by default. When it is not installed, BPF selftests build without
> errors, but tests_progs is unusable: it exits with the 255 code and
> without any error messages. When manually reproducing the issue, it is
> not too hard to find out that the generated verification_cert.h file is
> incorrect, but that's time consuming. When digging the BPF selftests
> build logs, this line can be seen amongst thousands others, but ignored:
>
> /bin/sh: 2: hexdump: not found
>
> Here, od is used with awk, instead of hexdump with sed. od is coming
> from the core utils package, and this new od command produces the same
> output when using od from GNU coreutils, uutils, and even busybox. This
> is more portable, and it produces the same results as what was done
> before with hexdump (without trailing whitespaces as a bonus).
>
> Fixes: b640d556a2b3 ("selftests/bpf: Remove xxd util dependency")
> Signed-off-by: Matthieu Baerts (NGI0) <[email protected]>
> ---
> Originally, I was going to add a check to stop the build if hexdump was
> not available, but switching to 'od' seems to be a better solution while
> not adding a new dependency.
>
> Because test_progs was not reporting why it became unusable, I added a
> Fixes tag to have this backported, to help others. Feel free to remove
> it, or even drop the patch if you prefer to stick with hexdump.
> ---
> tools/testing/selftests/bpf/Makefile | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/tools/testing/selftests/bpf/Makefile
> b/tools/testing/selftests/bpf/Makefile
> index c6bf4dfb1495..5a618d14243e 100644
> --- a/tools/testing/selftests/bpf/Makefile
> +++ b/tools/testing/selftests/bpf/Makefile
> @@ -723,7 +723,7 @@ $(VERIFICATION_CERT) $(PRIVATE_KEY): $(VERIFY_SIG_SETUP)
> # Generates a header with C array declaration, containing
> test_progs_verification_cert bytes
> $(VERIFY_SIG_HDR): $(VERIFICATION_CERT)
> $(Q)(echo "unsigned char test_progs_verification_cert[] = {"; \
> - hexdump -v -e '12/1 " 0x%02x," "\n"' $< | sed 's/0x ,//g;
> $$s/,$$//'; \
> + od -v -t 'xC' -w12 $< | awk 'NF > 1 {for (i=2; i<=NF; i++) { printf "
> 0x%s,", $$i }; printf "\n"}'; \
That is subtly different.
The hexdump version deletes the final ',' from the last full line.
But not a partial line because there are trailing spaces (from before
the '0x ,' that get removed).
That may not matter, it is valid C, but not C++ (unless they've changed
the rules recently).
od could be used with:
sed -e 's/ /, 0x/g; s/$/,/; s/^[0-7]*,//'
which outputs an empty line as well as the trailing ','.
Both removable with a more complex command line.
David
> echo "};"; \
> echo "unsigned int test_progs_verification_cert_len = $$(wc -c <
> $<);") > $@
>
>
> ---
> base-commit: 886bf921ecfc30f8f31341bc26560d8bf08b937b
> change-id: 20260216-bpf-sft-hexdump-od-abd07a3bf026
>
> Best regards,
