[PATCH v2 bpf 08/11] samples/bpf: fix false-positive right-shift underflow warnings

[Alexander Lobakin <alobakin@pm.me>]

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@fb.com>
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(-)

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