Messages in this thread | | | Date | Wed, 27 Apr 2022 08:54:53 -0700 | Subject | Re: [PATCH bpf-next 08/11] samples: bpf: fix shifting unsigned long by 32 positions | From | Yonghong Song <> |
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On 4/20/22 10:18 AM, Andrii Nakryiko wrote: > On Thu, Apr 14, 2022 at 3:46 PM Alexander Lobakin <alobakin@pm.me> wrote: >> >> On 32 bit systems, shifting an unsigned long by 32 positions >> yields the following warning: >> >> samples/bpf/tracex2_kern.c:60:23: warning: shift count >= width of type [-Wshift-count-overflow] >> unsigned int hi = v >> 32; >> ^ ~~ >> > > long is always 64-bit in BPF, but I suspect this is due to > samples/bpf/Makefile still using this clang + llc combo, where clang > is called with native target and llc for -target bpf. Not sure if we > are ready to ditch that complicated combination. Yonghong, do we still > need that or can we just use -target bpf in samples/bpf?
Current most bpf programs in samples/bpf do not use vmlinux.h and CO-RE. They direct use kernel header files. That is why clang C -> IR compilation still needs to be native.
We could just use -target bpf for the whole compilation but that needs to change the code to use vmlinux.h and CO-RE. There are already a couple of sample bpf programs did this.
> > >> The usual way to avoid this is to shift by 16 two times (see >> upper_32_bits() macro in the kernel). Use it across the BPF sample >> code as well. >> >> Fixes: d822a1926849 ("samples/bpf: Add counting example for kfree_skb() function calls and the write() syscall") >> Fixes: 0fb1170ee68a ("bpf: BPF based latency tracing") >> Fixes: f74599f7c530 ("bpf: Add tests and samples for LWT-BPF") >> Signed-off-by: Alexander Lobakin <alobakin@pm.me> >> --- >> samples/bpf/lathist_kern.c | 2 +- >> samples/bpf/lwt_len_hist_kern.c | 2 +- >> samples/bpf/tracex2_kern.c | 2 +- >> 3 files changed, 3 insertions(+), 3 deletions(-) >> > > [...]
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