Re: [PATCH bpf] selftests/bpf: Remove hexdump dependency

[Matthieu Baerts <matttbe@kernel.org>]

Hi David,

Thank you for the review!

On 17/02/2026 12:29, David Laight wrote:
> On Mon, 16 Feb 2026 17:30:34 +0100
> "Matthieu Baerts (NGI0)" <matttbe@kernel.org> 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) <matttbe@kernel.org>
>> ---
>> 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).

Good catch!

> That may not matter, it is valid C, but not C++ (unless they've changed
> the rules recently).
Is it an issue here? From what I see, this verification_cert.h file is
only used in test_progs.c.

> od could be used with:
> 	sed -e 's/ /,  0x/g; s/$/,/; s/^[0-7]*,//'
> which outputs an empty line as well as the trailing ','.

If adding an extra empty line is not a "visual" issue, I'm happy to
change to this shorter sed command if preferred!

> Both removable with a more complex command line.

Indeed. But if they don't cause issues, no need to remove them, right?

Cheers,
Matt
-- 
Sponsored by the NGI0 Core fund.