On Fri, 25 Oct 2024 at 21:15, Eric Biggers <ebiggers@xxxxxxxxxx> wrote: > > From: Eric Biggers <ebiggers@xxxxxxxxxx> > > Instead of registering the crc32-$arch and crc32c-$arch algorithms if > the arch-specific code was built, only register them when that code was > built *and* is not falling back to the base implementation at runtime. > > This avoids confusing users like btrfs which checks the shash driver > name to determine whether it is crc32c-generic. > I think we agree that 'generic' specifically means a C implementation that is identical across all architectures, which is why I updated my patch to export -arch instead of wrapping the C code in yet another driver just for the fuzzing tests. So why is this a problem? If no optimizations are available at runtime, crc32-arch and crc32-generic are interchangeable, and so it shouldn't matter whether you use one or the other. You can infer from the driver name whether the C code is being used, not whether or not the implementation is 'fast', and the btrfs hack is already broken on arm64. > (It would also make sense to change btrfs to test the crc32_optimization > flags itself, so that it doesn't have to use the weird hack of parsing > the driver name. This change still makes sense either way though.) > Indeed. That hack is very dubious and I'd be inclined just to ignore this. On x86 and arm64, it shouldn't make a difference, given that crc32-arch will be 'fast' in the vast majority of cases. On other architectures, btrfs may use the C implementation while assuming it is something faster, and if anyone actually notices the difference, we can work with the btrfs devs to do something more sensible here. > Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx> > --- > crypto/crc32_generic.c | 8 ++++++-- > crypto/crc32c_generic.c | 8 ++++++-- > 2 files changed, 12 insertions(+), 4 deletions(-) > > diff --git a/crypto/crc32_generic.c b/crypto/crc32_generic.c > index cc064ea8240e..cecd01e4d6e6 100644 > --- a/crypto/crc32_generic.c > +++ b/crypto/crc32_generic.c > @@ -155,19 +155,23 @@ static struct shash_alg algs[] = {{ > .base.cra_ctxsize = sizeof(u32), > .base.cra_module = THIS_MODULE, > .base.cra_init = crc32_cra_init, > }}; > > +static int num_algs; > + > static int __init crc32_mod_init(void) > { > /* register the arch flavor only if it differs from the generic one */ > - return crypto_register_shashes(algs, 1 + IS_ENABLED(CONFIG_CRC32_ARCH)); > + num_algs = 1 + ((crc32_optimizations & CRC32_LE_OPTIMIZATION) != 0); > + > + return crypto_register_shashes(algs, num_algs); > } > > static void __exit crc32_mod_fini(void) > { > - crypto_unregister_shashes(algs, 1 + IS_ENABLED(CONFIG_CRC32_ARCH)); > + crypto_unregister_shashes(algs, num_algs); > } > > subsys_initcall(crc32_mod_init); > module_exit(crc32_mod_fini); > > diff --git a/crypto/crc32c_generic.c b/crypto/crc32c_generic.c > index 04b03d825cf4..47d694da9d4a 100644 > --- a/crypto/crc32c_generic.c > +++ b/crypto/crc32c_generic.c > @@ -195,19 +195,23 @@ static struct shash_alg algs[] = {{ > .base.cra_ctxsize = sizeof(struct chksum_ctx), > .base.cra_module = THIS_MODULE, > .base.cra_init = crc32c_cra_init, > }}; > > +static int num_algs; > + > static int __init crc32c_mod_init(void) > { > /* register the arch flavor only if it differs from the generic one */ > - return crypto_register_shashes(algs, 1 + IS_ENABLED(CONFIG_CRC32_ARCH)); > + num_algs = 1 + ((crc32_optimizations & CRC32C_OPTIMIZATION) != 0); > + > + return crypto_register_shashes(algs, num_algs); > } > > static void __exit crc32c_mod_fini(void) > { > - crypto_unregister_shashes(algs, 1 + IS_ENABLED(CONFIG_CRC32_ARCH)); > + crypto_unregister_shashes(algs, num_algs); > } > > subsys_initcall(crc32c_mod_init); > module_exit(crc32c_mod_fini); > > -- > 2.47.0 > >