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Date: Thu, 21 Apr 2022 00:39:41 +0000 From: Alexander Lobakin <alobakin@...me> To: Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org> Cc: Alexander Lobakin <alobakin@...me>, Maciej Fijalkowski <maciej.fijalkowski@...el.com>, Song Liu <songliubraving@...com>, Kumar Kartikeya Dwivedi <memxor@...il.com>, bpf@...r.kernel.org, netdev@...r.kernel.org, linux-kernel@...r.kernel.org Subject: [PATCH v2 bpf 08/11] samples/bpf: fix false-positive right-shift underflow warnings 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; ^ ~~ sizeof(long) is always 8 for the BPF architecture, so this is not correct, but the BPF samples Makefile still uses the Clang native + LLC combo which enforces that. Until the samples are switched to `-target bpf`, do it the usual way: shift by 16 two times (see upper_32_bits() macro in the kernel). 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") Acked-by: Song Liu <songliubraving@...com> Signed-off-by: Alexander Lobakin <alobakin@...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(-) diff --git a/samples/bpf/lathist_kern.c b/samples/bpf/lathist_kern.c index 4adfcbbe6ef4..9744ed547abe 100644 --- a/samples/bpf/lathist_kern.c +++ b/samples/bpf/lathist_kern.c @@ -53,7 +53,7 @@ static unsigned int log2(unsigned int v) static unsigned int log2l(unsigned long v) { - unsigned int hi = v >> 32; + unsigned int hi = (v >> 16) >> 16; if (hi) return log2(hi) + 32; diff --git a/samples/bpf/lwt_len_hist_kern.c b/samples/bpf/lwt_len_hist_kern.c index 1fa14c54963a..bf32fa04c91f 100644 --- a/samples/bpf/lwt_len_hist_kern.c +++ b/samples/bpf/lwt_len_hist_kern.c @@ -49,7 +49,7 @@ static unsigned int log2(unsigned int v) static unsigned int log2l(unsigned long v) { - unsigned int hi = v >> 32; + unsigned int hi = (v >> 16) >> 16; if (hi) return log2(hi) + 32; else diff --git a/samples/bpf/tracex2_kern.c b/samples/bpf/tracex2_kern.c index 5bc696bac27d..6bf22056ff95 100644 --- a/samples/bpf/tracex2_kern.c +++ b/samples/bpf/tracex2_kern.c @@ -57,7 +57,7 @@ static unsigned int log2(unsigned int v) static unsigned int log2l(unsigned long v) { - unsigned int hi = v >> 32; + unsigned int hi = (v >> 16) >> 16; if (hi) return log2(hi) + 32; else -- 2.36.0
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