[PATCH bpf] selftests/bpf: Remove hexdump dependency

[PATCH bpf] selftests/bpf: Remove hexdump dependency

[Matthieu Baerts (NGI0)]

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,", $$i }; printf "\n"}'; \
 	 echo "};"; \
 	 echo "unsigned int test_progs_verification_cert_len = $$(wc -c < $<);") > $@
 

---
base-commit: 886bf921ecfc30f8f31341bc26560d8bf08b937b
change-id: 20260216-bpf-sft-hexdump-od-abd07a3bf026

Best regards,
-- 
Matthieu Baerts (NGI0) <matttbe@kernel.org>

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

[Mykyta Yatsenko]

On 2/16/26 16:30, Matthieu Baerts (NGI0) 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,", $$i }; printf "\n"}'; \
>   	 echo "};"; \
>   	 echo "unsigned int test_progs_verification_cert_len = $$(wc -c < $<);") > $@
>   
>
> ---
> base-commit: 886bf921ecfc30f8f31341bc26560d8bf08b937b
> change-id: 20260216-bpf-sft-hexdump-od-abd07a3bf026
>
> Best regards,
Works well.
Tested-by: Mykyta Yatsenko <yatsenko@meta.com>

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

[David Laight]

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).
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,

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

[Matthieu Baerts]

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.