| Message ID | 20200621142559.GA25517@stranger.qboosh.pl |
|---|---|
| State | Changes Requested |
| Delegated to: | BPF Maintainers |
| Headers | show |
| Series | fix libbpf hashmap with size_t shorter than long long | expand |
On Sun, Jun 21, 2020 at 7:34 AM Jakub Bogusz <qboosh@pld-linux.org> wrote: > > Hello, > > I noticed that _bpftool crashes when building kernel tools (5.7.x) for > 32-bit targets because in libbpf hashmap implementation hash_bits() > function returning numbers exceeding hashmap buckets capacity. > > Attached patch fixes this problem. > Thanks! But this was already fixed by Arnaldo Carvalho de Melo <acme@kernel.org> in 8ca8d4a84173 ("libbpf: Define __WORDSIZE if not available"). > > Regards, > > -- > Jakub Bogusz http://qboosh.pl/
On Mon, Jun 22, 2020 at 10:44:56PM -0700, Andrii Nakryiko wrote: > On Sun, Jun 21, 2020 at 7:34 AM Jakub Bogusz <qboosh@pld-linux.org> wrote: > > > > Hello, > > > > I noticed that _bpftool crashes when building kernel tools (5.7.x) for > > 32-bit targets because in libbpf hashmap implementation hash_bits() > > function returning numbers exceeding hashmap buckets capacity. > > > > Attached patch fixes this problem. > > > > Thanks! But this was already fixed by Arnaldo Carvalho de Melo <acme@kernel.org> > in 8ca8d4a84173 ("libbpf: Define __WORDSIZE if not available"). No, it's not: This change worked around __WORDSIZE not always being available. But the issue on (I)LP32 platforms is that 64-bit value is shifted by (32-bits) instead of (64-bits). (__SIZEOF_LONG__ * 8) is 32 on such architectures (i686, arm). I used __SIZEOF_LONG_LONG__ to get proper bit shift both on (I)LP32 and LP64 architectures. Should I provide an updated patch to apply on top of acme change? Regards,
On Tue, Jun 23, 2020 at 12:29 PM Jakub Bogusz <qboosh@pld-linux.org> wrote: > > On Mon, Jun 22, 2020 at 10:44:56PM -0700, Andrii Nakryiko wrote: > > On Sun, Jun 21, 2020 at 7:34 AM Jakub Bogusz <qboosh@pld-linux.org> wrote: > > > > > > Hello, > > > > > > I noticed that _bpftool crashes when building kernel tools (5.7.x) for > > > 32-bit targets because in libbpf hashmap implementation hash_bits() > > > function returning numbers exceeding hashmap buckets capacity. > > > > > > Attached patch fixes this problem. > > > > > > > Thanks! But this was already fixed by Arnaldo Carvalho de Melo <acme@kernel.org> > > in 8ca8d4a84173 ("libbpf: Define __WORDSIZE if not available"). > > No, it's not: > This change worked around __WORDSIZE not always being available. > > But the issue on (I)LP32 platforms is that 64-bit value is shifted by > (32-bits) instead of (64-bits). > > (__SIZEOF_LONG__ * 8) is 32 on such architectures (i686, arm). > I used __SIZEOF_LONG_LONG__ to get proper bit shift both on (I)LP32 and > LP64 architectures. > Ah, I see. I actually mentioned __SIZEOF_ constants on the original fix patch. But I think in this case it has to use __SIZEOF_SIZE_T, which on 32-bit should be 4, right? > Should I provide an updated patch to apply on top of acme change? Yes, that would be good. But I think there is no need to penalize 32-bit arches with use of 64-bit long longs, and instead it's better to use #ifdef for 32-bit case vs 64-bit case. The multiplication constant will change, of course, should be 2654435769. I'd appreciate it if you can do the patch, thanks! > > > Regards, > > -- > Jakub Bogusz http://qboosh.pl/
On Tue, Jun 23, 2020 at 12:40:02PM -0700, Andrii Nakryiko wrote: > On Tue, Jun 23, 2020 at 12:29 PM Jakub Bogusz <qboosh@pld-linux.org> wrote: > > > > On Mon, Jun 22, 2020 at 10:44:56PM -0700, Andrii Nakryiko wrote: > > > On Sun, Jun 21, 2020 at 7:34 AM Jakub Bogusz <qboosh@pld-linux.org> wrote: > > > > > > > > Hello, > > > > > > > > I noticed that _bpftool crashes when building kernel tools (5.7.x) for > > > > 32-bit targets because in libbpf hashmap implementation hash_bits() > > > > function returning numbers exceeding hashmap buckets capacity. > > > > > > > > Attached patch fixes this problem. > > > > > > > > > > Thanks! But this was already fixed by Arnaldo Carvalho de Melo <acme@kernel.org> > > > in 8ca8d4a84173 ("libbpf: Define __WORDSIZE if not available"). > > > > No, it's not: > > This change worked around __WORDSIZE not always being available. > > > > But the issue on (I)LP32 platforms is that 64-bit value is shifted by > > (32-bits) instead of (64-bits). > > > > (__SIZEOF_LONG__ * 8) is 32 on such architectures (i686, arm). > > I used __SIZEOF_LONG_LONG__ to get proper bit shift both on (I)LP32 and > > LP64 architectures. > > > > Ah, I see. I actually mentioned __SIZEOF_ constants on the original > fix patch. But I think in this case it has to use __SIZEOF_SIZE_T, > which on 32-bit should be 4, right? After changing constant to 32-bit, yes (to be precise, it should use maximum of __SIZEOF_SIZE_T__ and __SIZEOF_LONG__ if constant is specified with UL suffix; there is no constant suffix available for size_t). > > Should I provide an updated patch to apply on top of acme change? > > Yes, that would be good. But I think there is no need to penalize > 32-bit arches with use of 64-bit long longs, and instead it's better > to use #ifdef for 32-bit case vs 64-bit case. The multiplication > constant will change, of course, should be 2654435769. I'd appreciate > it if you can do the patch, thanks! OK, so now the patch provides two variants: - "long long" case for LP64 architectures - "long" case for (I)LP32 architectures (selected basing of __SIZEOF_ constants) matter) Regards,
On Sat, Jun 27, 2020 at 2:07 AM Jakub Bogusz <qboosh@pld-linux.org> wrote: > > On Tue, Jun 23, 2020 at 12:40:02PM -0700, Andrii Nakryiko wrote: > > On Tue, Jun 23, 2020 at 12:29 PM Jakub Bogusz <qboosh@pld-linux.org> wrote: > > > > > > On Mon, Jun 22, 2020 at 10:44:56PM -0700, Andrii Nakryiko wrote: > > > > On Sun, Jun 21, 2020 at 7:34 AM Jakub Bogusz <qboosh@pld-linux.org> wrote: > > > > > > > > > > Hello, > > > > > > > > > > I noticed that _bpftool crashes when building kernel tools (5.7.x) for > > > > > 32-bit targets because in libbpf hashmap implementation hash_bits() > > > > > function returning numbers exceeding hashmap buckets capacity. > > > > > > > > > > Attached patch fixes this problem. > > > > > > > > > > > > > Thanks! But this was already fixed by Arnaldo Carvalho de Melo <acme@kernel.org> > > > > in 8ca8d4a84173 ("libbpf: Define __WORDSIZE if not available"). > > > > > > No, it's not: > > > This change worked around __WORDSIZE not always being available. > > > > > > But the issue on (I)LP32 platforms is that 64-bit value is shifted by > > > (32-bits) instead of (64-bits). > > > > > > (__SIZEOF_LONG__ * 8) is 32 on such architectures (i686, arm). > > > I used __SIZEOF_LONG_LONG__ to get proper bit shift both on (I)LP32 and > > > LP64 architectures. > > > > > > > Ah, I see. I actually mentioned __SIZEOF_ constants on the original > > fix patch. But I think in this case it has to use __SIZEOF_SIZE_T, > > which on 32-bit should be 4, right? > > After changing constant to 32-bit, yes (to be precise, it should use maximum > of __SIZEOF_SIZE_T__ and __SIZEOF_LONG__ if constant is specified with > UL suffix; there is no constant suffix available for size_t). > > > > Should I provide an updated patch to apply on top of acme change? > > > > Yes, that would be good. But I think there is no need to penalize > > 32-bit arches with use of 64-bit long longs, and instead it's better > > to use #ifdef for 32-bit case vs 64-bit case. The multiplication > > constant will change, of course, should be 2654435769. I'd appreciate > > it if you can do the patch, thanks! > > OK, so now the patch provides two variants: > - "long long" case for LP64 architectures > - "long" case for (I)LP32 architectures > (selected basing of __SIZEOF_ constants) > matter) > > Change looks good, thanks! But it would be more convenient for everyone if you submitted it not as an attachment, but as a proper patch email message. Acked-by: Andrii Nakryiko <andriin@fb.com> > Regards, > > -- > Jakub Bogusz http://qboosh.pl/
--- linux-5.7/tools/lib/bpf/hashmap.h.orig 2020-06-01 01:49:15.000000000 +0200 +++ linux-5.7/tools/lib/bpf/hashmap.h 2020-06-21 15:22:07.298466419 +0200 @@ -10,17 +10,12 @@ #include <stdbool.h> #include <stddef.h> -#ifdef __GLIBC__ -#include <bits/wordsize.h> -#else -#include <bits/reg.h> -#endif #include "libbpf_internal.h" static inline size_t hash_bits(size_t h, int bits) { /* shuffle bits and return requested number of upper bits */ - return (h * 11400714819323198485llu) >> (__WORDSIZE - bits); + return (h * 11400714819323198485llu) >> (__SIZEOF_LONG_LONG__ * 8 - bits); } typedef size_t (*hashmap_hash_fn)(const void *key, void *ctx);