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Bugfix: mark outputs as early clobber in scalar x86_64 asm

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In the existing code, the compiler is allowed to allocate the RSI register
for outputs m0, m1, or m2, which are written to before the input in RSI is
read from. Fix this by marking them as early clobber.

Reported by ehoffman2 in https://github.com/bitcoin-core/secp256k1/issues/766
This commit is contained in:
Pieter Wuille 2023-05-12 05:15:05 -04:00 committed by Jonas Nick
parent c8c0f55a11
commit 56a5d41429
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1 changed files with 1 additions and 1 deletions
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src/scalar_4x64_impl.h
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@ -389,7 +389,7 @@ static void secp256k1_scalar_reduce_512(secp256k1_scalar *r, const uint64_t *l)
"movq %%r10, %q5\n"
/* extract m6 */
"movq %%r8, %q6\n"
: "=g"(m0), "=g"(m1), "=g"(m2), "=g"(m3), "=g"(m4), "=g"(m5), "=g"(m6)
: "=&g"(m0), "=&g"(m1), "=&g"(m2), "=g"(m3), "=g"(m4), "=g"(m5), "=g"(m6)
: "S"(l), "i"(SECP256K1_N_C_0), "i"(SECP256K1_N_C_1)
: "rax", "rdx", "r8", "r9", "r10", "r11", "r12", "r13", "r14", "cc");