Yes, it’s undefined behavior for __builtin_clz with 0 input.
And it seems rare to initialize bihash with 0 bucket, but not sure of the input
for other use cases with min_log2/max_log2.
Or, there could be a “ASSERT (x != 0)” in min_log2/max_log2 to alert 0 input.
[1]
https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html
Built-in Function: int __builtin_clz (unsigned int x)
Returns the number of leading 0-bits in x, starting at the most significant bit
position. If x is 0, the result is undefined.
Thanks.
From: vpp-dev@lists.fd.io On Behalf Of NUAA?? via
lists.fd.io
Sent: Monday, October 10, 2022 11:11 AM
To: vpp-dev@lists.fd.io
Subject: [vpp-dev] vpp-2206 bug
Hi, vpp experts
when i use bihash_init_8_8 ( p, "test"，0，0）function in arm64 machine, it will
cause abort()
gcc version is 9.3.0
the reason is when buckets is 0, src/vppinfra/clib.h min_log2() function will
use count_leading_zero(0), but return value is different between x86 and
arm64，x86 is 63 but arm64 is 64, it is a undefined behavior for compiler, so
min_log2() need add a judgement with it
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