From: Tyler Retzlaff <roretzla@linux.microsoft.com>
To: Stephen Hemminger <stephen@networkplumber.org>
Cc: dev@dpdk.org
Subject: Re: RFC acceptable handling of VLAs across toolchains
Date: Thu, 9 Nov 2023 12:26:48 -0800 [thread overview]
Message-ID: <20231109202648.GA7506@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net> (raw)
In-Reply-To: <20231108085154.757719e4@hermes.local>
On Wed, Nov 08, 2023 at 08:51:54AM -0800, Stephen Hemminger wrote:
> On Tue, 7 Nov 2023 11:32:20 -0800
> Tyler Retzlaff <roretzla@linux.microsoft.com> wrote:
>
> > hi folks,
> >
> > i'm seeking advice. we have use of VLAs which are now optional in
> > standard C. some toolchains provide a conformant implementation and msvc
> > does not (and never will).
> >
> > we seem to have a few options, just curious about what people would
> > prefer.
> >
> > * use alloca
> >
> > * use dynamically allocated storage
> >
> > * conditional compiled code where the msvc leg uses one of the previous
> > two options
> >
> > i'll leave it simple for now, i'd like to hear input rather than provide
> > a recommendation for now.
> >
> > thanks!
>
> As an experiment did a build of current DPDK with -Wvla option.
so maybe what i will do here is put a series up that convers to alloca()
for libs and enables -Wvla as a part of the review we can discuss
case-by-case basis of keeping alloca or converting to regular C arrays?
for the items identified below i'll make the conversions as you have
suggested in v1 of the series and seek further comment.
>
> Lots of errors, some have obvious solutions like:
>
> ../drivers/net/failsafe/failsafe_intr.c: In function ‘fs_rx_event_proxy_service_install’:
> ../drivers/net/failsafe/failsafe_intr.c:142:17: warning: ISO C90 forbids variable length array ‘service_core_list’ [-Wvla]
> 142 | uint32_t service_core_list[num_service_cores];
> | ^~~~~~~~
>
> This could just be RTE_MAX_LCORES.
>
> others like rte_metrics should just use malloc() as is used already in
> that function.
>
> ../lib/metrics/rte_metrics_telemetry.c: In function ‘rte_metrics_tel_update_metrics_ethdev’:
> ../lib/metrics/rte_metrics_telemetry.c:140:9: warning: ISO C90 forbids variable length array ‘xstats_values’ [-Wvla]
> 140 | uint64_t xstats_values[num_xstats];
> | ^~~~~~~~
> ../lib/metrics/rte_metrics_telemetry.c: In function ‘rte_metrics_tel_extract_data’:
> ../lib/metrics/rte_metrics_telemetry.c:384:9: warning: ISO C90 forbids variable length array ‘stat_names’ [-Wvla]
> 384 | const char *stat_names[num_stat_names];
> | ^~~~~
>
> Others already have an implicit upper bound.
> Example is in rte_cuckoo_hash where some fields us RTE_HASH_LOOKUP_BULK_MAX
> and some use VLA.
>
> [170/2868] Compiling C object lib/librte_hash.a.p/hash_rte_cuckoo_hash.c.o
> ../lib/hash/rte_cuckoo_hash.c: In function ‘rte_hash_lookup_bulk_data’:
> ../lib/hash/rte_cuckoo_hash.c:2355:9: warning: ISO C90 forbids variable length array ‘positions’ [-Wvla]
> 2355 | int32_t positions[num_keys];
> | ^~~~~~~
> ../lib/hash/rte_cuckoo_hash.c: In function ‘rte_hash_lookup_with_hash_bulk_data’:
> ../lib/hash/rte_cuckoo_hash.c:2471:9: warning: ISO C90 forbids variable length array ‘positions’ [-Wvla]
> 2471 | int32_t positions[num_keys];
> | ^~~~~~~
>
> Would it make sense to have an rte_config.h value for maximum burst size?
> Lots of code is using nb_pkts.
>
> There is also some confusing ones like:
> ../lib/mempool/rte_mempool.c: In function ‘mempool_cache_init’:
> ../lib/mempool/rte_mempool.c:751:50: warning: ISO C90 forbids array whose size cannot be evaluated [-Wvla]
> 751 | RTE_SIZEOF_FIELD(struct rte_mempool_cache, objs[0]));
> | ^~~~~~~~~~~~~~~~~
> ../lib/eal/include/rte_common.h:498:65: note: in definition of macro ‘RTE_BUILD_BUG_ON’
> 498 | #define RTE_BUILD_BUG_ON(condition) ((void)sizeof(char[1 - 2*!!(condition)]))
> | ^~~~~~~~~
> ../lib/mempool/rte_mempool.c:751:26: note: in expansion of macro ‘RTE_SIZEOF_FIELD’
> 751 | RTE_SIZEOF_FIELD(struct rte_mempool_cache, objs[0]));
next prev parent reply other threads:[~2023-11-09 20:26 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-11-07 19:32 Tyler Retzlaff
2023-11-08 2:31 ` Stephen Hemminger
2023-11-08 3:25 ` Tyler Retzlaff
2023-11-08 8:19 ` Morten Brørup
2023-11-08 16:51 ` Stephen Hemminger
2023-11-08 17:48 ` Morten Brørup
2023-11-09 10:25 ` RFC: default burst sizes in rte_config Morten Brørup
2023-11-09 20:26 ` Tyler Retzlaff [this message]
2024-03-21 0:12 ` RFC acceptable handling of VLAs across toolchains Tyler Retzlaff
2024-04-04 17:15 ` [PATCH 0/4] RFC samples converting VLA to alloca Tyler Retzlaff
2024-04-04 17:15 ` [PATCH 1/4] latencystats: use alloca instead of vla trivial Tyler Retzlaff
2024-04-06 15:28 ` Morten Brørup
2024-04-07 9:36 ` Mattias Rönnblom
2024-04-07 17:00 ` Stephen Hemminger
2024-04-04 17:15 ` [PATCH 2/4] hash: " Tyler Retzlaff
2024-04-06 16:01 ` Morten Brørup
2024-04-04 17:15 ` [PATCH 3/4] vhost: use alloca instead of vla sizeof Tyler Retzlaff
2024-04-06 22:30 ` Morten Brørup
2024-04-04 17:15 ` [PATCH 4/4] dispatcher: use alloca instead of vla multi dimensional Tyler Retzlaff
2024-04-06 15:49 ` Morten Brørup
2024-04-07 9:31 ` [PATCH 0/4] RFC samples converting VLA to alloca Mattias Rönnblom
2024-04-07 11:07 ` Morten Brørup
2024-04-07 17:03 ` Stephen Hemminger
2024-04-08 15:27 ` Tyler Retzlaff
2024-04-08 15:53 ` Morten Brørup
2024-04-09 8:28 ` Konstantin Ananyev
2024-04-09 15:08 ` Tyler Retzlaff
2024-04-10 9:58 ` Konstantin Ananyev
2024-04-10 17:03 ` Tyler Retzlaff
2024-04-10 7:32 ` Mattias Rönnblom
2024-04-10 7:52 ` Morten Brørup
2024-04-10 17:04 ` Tyler Retzlaff
2024-04-10 7:27 ` Mattias Rönnblom
2024-04-10 17:10 ` Tyler Retzlaff
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