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BLAKE2b has a state of 16 64-bit words. Add the message data in and
there are 32 64-bit words. With the current code where all the rounds
are unrolled to enable constant-folding of the blake2b_sigma values,
this results in a very large code size on 32-bit kernels, including a
recurring issue where gcc uses a large amount of stack.
There's just not much benefit to this unrolling when the code is already
so large. Let's roll up the rounds when !CONFIG_64BIT.
To avoid having to duplicate the code, just write the code once using a
loop, and conditionally use 'unrolled_full' from <linux/unroll.h>.
Then, fold the now-unneeded ROUND() macro into the loop. Finally, also
remove the now-unneeded override of the stack frame size warning.
Code size improvements for blake2b_compress_generic():
Size before (bytes) Size after (bytes)
------------------- ------------------
i386, gcc 27584 3632
i386, clang 18208 3248
arm32, gcc 19912 2860
arm32, clang 21336 3344
Running the BLAKE2b benchmark on a !CONFIG_64BIT kernel on an x86_64
processor shows a 16384B throughput change of 351 => 340 MB/s (gcc) or
442 MB/s => 375 MB/s (clang). So clearly not much of a slowdown either.
But also that microbenchmark also effectively disregards cache usage,
which is important in practice and is far better in the smaller code.
Note: If we rolled up the loop on x86_64 too, the change would be
7024 bytes => 1584 bytes and 1960 MB/s => 1396 MB/s (gcc), or
6848 bytes => 1696 bytes and 1920 MB/s => 1263 MB/s (clang).
Maybe still worth it, though not quite as clearly beneficial.
Fixes: 91d689337f ("crypto: blake2b - add blake2b generic implementation")
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20251205050330.89704-1-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>
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