On Fri, Nov 15, 2024 at 11:57:24AM -0800, Andrii Nakryiko wrote:
> On Fri, Nov 15, 2024 at 2:51 AM Sidong Yang <sidong.yang@xxxxxxxxxx> wrote:
> >
> > The hash_combine() could be trapped when compiled with sanitizer like "zig cc".
> > This patch changes parameters to __u32 to fix it.
>
> Can you please elaborate? What exactly are you fixing? "Undefined"
> signed integer overflow? I can consider changing long to unsigned
> long, but I don't think we should downgrade from long all the way to
> 32-bit u32. I'd rather keep all those 64 bits for hash.
Hi, Andrii.
Actually I'm using libbpf-rs with maturin build that makes python package for
rust. It seems that it uses zig cc for cross compilation. It compiles libbpf
like this command.
CC="zig cc" make CFLAGS="-fsanitize-trap"
And hash_combine's result is like below.
0000000000063860 <hash_combine>:
63860: 55 push %rbp
63861: 48 89 e5 mov %rsp,%rbp
63864: 48 89 7d f8 mov %rdi,-0x8(%rbp)
63868: 48 89 75 f0 mov %rsi,-0x10(%rbp)
6386c: b8 1f 00 00 00 mov $0x1f,%eax
63871: 48 0f af 45 f8 imul -0x8(%rbp),%rax
63876: 48 89 45 e8 mov %rax,-0x18(%rbp)
6387a: 0f 90 c0 seto %al
6387d: 34 ff xor $0xff,%al
6387f: a8 01 test $0x1,%al
63881: 0f 85 05 00 00 00 jne 6388c <hash_combine+0x2c>
-> 63887: 67 0f b9 40 0c ud1 0xc(%eax),%eax
6388c: 48 8b 45 e8 mov -0x18(%rbp),%rax
63890: 48 03 45 f0 add -0x10(%rbp),%rax
63894: 48 89 45 e0 mov %rax,-0x20(%rbp)
63898: 0f 90 c0 seto %al
6389b: 34 ff xor $0xff,%al
6389d: a8 01 test $0x1,%al
6389f: 0f 85 04 00 00 00 jne 638a9 <hash_combine+0x49>
638a5: 67 0f b9 00 ud1 (%eax),%eax
638a9: 48 8b 45 e0 mov -0x20(%rbp),%rax
638ad: 5d pop %rbp
638ae: c3 ret
638af: 90 nop
When I'm using libbpf-rs, it receives SIGILL for ud1 instruction.
It seems more appropriate to use u64 instead of u32, doesn't it?
I'll work on it.
Thanks,
Sidong
>
> pw-bot: cr
>
> >
> > Signed-off-by: Sidong Yang <sidong.yang@xxxxxxxxxx>
> > ---
> > tools/lib/bpf/btf.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
> > index 8befb8103e32..11ccb5aa4958 100644
> > --- a/tools/lib/bpf/btf.c
> > +++ b/tools/lib/bpf/btf.c
> > @@ -3548,7 +3548,7 @@ struct btf_dedup {
> > struct strset *strs_set;
> > };
> >
> > -static long hash_combine(long h, long value)
> > +static __u32 hash_combine(__u32 h, __u32 value)
> > {
> > return h * 31 + value;
> > }
> > --
> > 2.42.0
> >
> >
