On 7/29/20 12:13 PM, Jesper Dangaard Brouer wrote:
The BPF UAPI header file <linux/bpf.h> includes <linux/types.h>, which gives BPF-programs access to types e.g. __u32, __u64, __u8, etc. On Ubuntu/Debian when compiling with clang option[1] "-target bpf" the compile fails because it cannot find the file <asm/types.h>, which is included from <linux/types.h>. This is because Ubuntu/Debian tries to support multiple architectures on a single system[2]. On x86_64 the file <asm/types.h> is located in /usr/include/x86_64-linux-gnu/, which the distro compiler will add to it's search path (/usr/include/<triplet> [3]). Note, it works if not specifying target bpf, but as explained in kernel doc[1] the clang target bpf should really be used (to avoid other issues). There are two workarounds: (1) To have an extra include dir on Ubuntu (which seems too x86 specific) like: CFLAGS += -I/usr/include/x86_64-linux-gnu .
How about non x86 architecture? It will be something like /usr/include/aarch64-linux-gnu? Do you think we could have some header file conflict
since this directory may contain a lot other header files as well?
Or (2) install the package gcc-multilib on Ubuntu.
I think having a /usr/include/bpf-unknown-none and the distro add this path to the compiler has target bpf. In this way, only necessary header files will be put there. Less potential issues. But in either case, it will be good if this level of details are hidden from the user.I am not super familiar with the distro packaging of a particular compiler and its include directories. The above is just my 2 cents.
The question is: Should Ubuntu/Debian have a /usr/include/<triplet> directory for BPF? (as part of their multi-arch approach) Or should clang use the compile-host's triplet for the /usr/include/triplet path even when giving clang -target bpf option? p.s. GCC choose 'bpf-unknown-none' target triplet for BPF. Links: [1] https://www.kernel.org/doc/html/latest/bpf/bpf_devel_QA.html#q-clang-flag-for-target-bpf [2] https://urldefense.proofpoint.com/v2/url?u=https-3A__wiki.ubuntu.com_MultiarchSpec&d=DwICAg&c=5VD0RTtNlTh3ycd41b3MUw&r=DA8e1B5r073vIqRrFz7MRA&m=ZEguArah72427WZMt53NXZa8LuQEGJKvCOgjH96NggQ&s=5xL0VWya8ULHcj4pfw6oxqHoKWIXNfJnj2G7rdaQyR8&e= [3] https://urldefense.proofpoint.com/v2/url?u=https-3A__wiki.osdev.org_Target-5FTriplet&d=DwICAg&c=5VD0RTtNlTh3ycd41b3MUw&r=DA8e1B5r073vIqRrFz7MRA&m=ZEguArah72427WZMt53NXZa8LuQEGJKvCOgjH96NggQ&s=mym8eKus7o0PzfkC2-IMyPU84OwVb2_A4ky2JHcdexQ&e=
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