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Arnd Bergmann
065f978a0e
During randconfig testing, I came across a lot of warnings for the newly added carryless multiplication function triggering excessive stack usage from spilling temporary variables to the stack: lib/crypto/gf128hash.c:166:1: error: stack frame size (1192) exceeds limit (1024) in 'polyval_mul_generic' [-Werror,-Wframe-larger-than] In addition to the possible risk of overflowing the kernel stack, the generated object code surely performs very poorly. This only happens on architectures that don't provide uint128_t (which should be all 32-bit architectures on modern compilers), but though I tested random x86 and arm configs, I only saw this with arm's CONFIG_THUMB2_KERNEL, which adds more pressure to the register allocator. The testing was done using clang-22, I don't know if gcc has the same problem. Marking clmul32() as noinline_for_stack experimentally shows all of the affected builds to completely solve the problem, reducing the stack usage to a few bytes as expected. Since u64 arithmetic frequently leads to compilers badly optimizing 32-bit targets, keeping clmul32 out of line is likely to help on other 32-bit configurations as well when they run into this problem, though it may also result in a small performance degradation in configurations that would benefit from inlining. Signed-off-by: Arnd Bergmann <arnd@arndb.de> Link: https://patch.msgid.link/20260611125952.3387258-1-arnd@kernel.org Signed-off-by: Eric Biggers <ebiggers@kernel.org>