[PATCH] build: fix libpcap detection with unusable header

[Bruce Richardson]

On Tue, Jul 07, 2026 at 04:30:28PM +0300, Maayan Kashani wrote:
> The libpcap detection only checked that the library was present, that
> <pcap.h> could be included, and that a trivial program links. None of
> these fail when a distribution ships a libpcap-devel package whose
> <pcap.h> is empty (present but declaring nothing) while libpcap.so is
> installed: has_header() passes on an empty file and the link test does
> not reference any pcap symbol. RTE_HAS_LIBPCAP was then set and the
> pcap-dependent code (bpf_convert.c, port source/sink, dumpcap) failed
> to build with errors such as:
> 

Why would a distribution ship a devel package with an empty header file for
pcap.h? Is that expected behaviour in some scenario that I'm unaware of,
because it seems strange to me?

/Bruce

>   bpf_convert.c: error: invalid use of undefined type
>                  'const struct bpf_insn'
> 
> Require an actual pcap declaration (pcap_create) to be visible in the
> header before enabling libpcap support, so a broken or empty header
> disables the optional pcap features instead of breaking the build.
> 
> Fixes: d6024c0a6757 ("build: cleanup libpcap dependent components")
> Cc: stable at dpdk.org
> 
> Signed-off-by: Maayan Kashani <mkashani at nvidia.com>
> ---
>  config/meson.build | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/config/meson.build b/config/meson.build
> index d7f5e55c18f..4bfb8535781 100644
> --- a/config/meson.build
> +++ b/config/meson.build
> @@ -290,7 +290,10 @@ if not pcap_dep.found()
>      # pcap got a pkg-config file only in 1.9.0
>      pcap_dep = cc.find_library(pcap_lib, required: false)
>  endif
> -if (pcap_dep.found() and cc.has_header('pcap.h', dependencies: pcap_dep)
> +# has_header() passes even when pcap.h is empty; require a real declaration.
> +if (pcap_dep.found()
> +        and cc.has_header_symbol('pcap.h', 'pcap_create', dependencies: pcap_dep,
> +                args: '-D_GNU_SOURCE')
>          and cc.links(min_c_code, dependencies: pcap_dep))
>      dpdk_conf.set('RTE_HAS_LIBPCAP', 1)
>      dpdk_extra_ldflags += '-l at 0@'.format(pcap_lib)
> -- 
> 2.21.0
>