Messages in this thread | | | Date | Fri, 04 Aug 2017 20:44:43 +0200 | From | Daniel Borkmann <> | Subject | Re: [PATCH] samples/bpf: Fix cross compiler error with bpf sample |
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On 08/04/2017 08:33 PM, Joel Fernandes wrote: > On Fri, Aug 4, 2017 at 6:58 AM, Daniel Borkmann <daniel@iogearbox.net> wrote: >> On 08/04/2017 07:46 AM, Joel Fernandes wrote: >>> >>> When cross-compiling the bpf sample map_perf_test for aarch64, I find that >>> __NR_getpgrp is undefined. This causes build errors. Fix it by allowing >>> the >>> deprecated syscall in the sample. >>> >>> Signed-off-by: Joel Fernandes <joelaf@google.com> >>> --- >>> samples/bpf/map_perf_test_user.c | 2 ++ >>> 1 file changed, 2 insertions(+) >>> >>> diff --git a/samples/bpf/map_perf_test_user.c >>> b/samples/bpf/map_perf_test_user.c >>> index 1a8894b5ac51..6e6fc7121640 100644 >>> --- a/samples/bpf/map_perf_test_user.c >>> +++ b/samples/bpf/map_perf_test_user.c >>> @@ -8,7 +8,9 @@ >>> #include <sched.h> >>> #include <stdio.h> >>> #include <sys/types.h> >>> +#define __ARCH_WANT_SYSCALL_DEPRECATED >>> #include <asm/unistd.h> >>> +#undef __ARCH_WANT_SYSCALL_DEPRECATED >> >> >> So the only arch that sets __ARCH_WANT_SYSCALL_DEPRECATED >> is score: >> >> $ git grep -n __ARCH_WANT_SYSCALL_DEPRECATED >> arch/score/include/uapi/asm/unistd.h:7:#define >> __ARCH_WANT_SYSCALL_DEPRECATED >> include/uapi/asm-generic/unistd.h:837:#ifdef >> __ARCH_WANT_SYSCALL_DEPRECATED >> include/uapi/asm-generic/unistd.h:899:#endif /* >> __ARCH_WANT_SYSCALL_DEPRECATED */ >> >> But even if this would make aarch64 compile, the syscall >> numbers don't match up: >> >> $ git grep -n __NR_getpgrp include/uapi/asm-generic/unistd.h >> include/uapi/asm-generic/unistd.h:841:#define __NR_getpgrp 1060 >> include/uapi/asm-generic/unistd.h:843:__SYSCALL(__NR_getpgrp, sys_getpgrp) >> >> The only thing that can be found on arm64 is: >> >> $ git grep -n __NR_getpgrp arch/arm64/ >> arch/arm64/include/asm/unistd32.h:154:#define __NR_getpgrp 65 >> arch/arm64/include/asm/unistd32.h:155:__SYSCALL(__NR_getpgrp, sys_getpgrp) >> >> In arch/arm64/include/asm/unistd.h, it does include the >> uapi/asm/unistd.h when compat is not set, but without the >> __ARCH_WANT_SYSCALL_DEPRECATED. That doesn't look correct >> unless I'm missing something, hmm, can't we just attach the >> kprobes to a different syscall, one that is not deprecated, >> so that we don't run into this in the first place? > > Yes, I agree that's better. I think we can use getpgid. I'll try to > whip something today and send it out.
Ok, cool. Please make sure that this doesn't clash with anything else attached to map_perf_test_kern.c already given the obj file is loaded first with the attachment points.
> I also wanted to fix something else, HOSTCC is set to gcc, but I want > the boostrap part of the sample to run an ARM so I have to make HOSTCC > my cross-compiler. Right now I'm hacking it to point to the arm64 gcc > however I think I'd like to add a 'cross compile mode' or something > whether HOSTCC points to CROSS_COMPILE instead. I'm happy to discuss > any ideas to get this fixed too.
Yeah, sounds like a good idea to add such possibility. In case of cross compiling to a target arch with different endianess, you might also need to specifically select bpfeb (big endian) resp. bpfel (little endian) as clang target. (Just bpf target uses host endianess.)
Thanks, Joel!
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