arm one-shot chacha_armv6 stores data below stack pointer

[yumkam]

E.g.

chacha-opt/app/extensions/chacha/chacha_armv6-32.inc

Line 440 in d69e5ac

stmia sp!, {r4-r5}

This stores data below stack pointer, then move pointer back, and expect same data still there.

chacha-opt/app/extensions/chacha/chacha_armv6-32.inc

Line 445 in d69e5ac

sub sp, sp, #48

I could be wrong, but as I don't see anything like amd64's "red zone" in arm ABI documentation, so this looks incorrect (application cannot rely on data stored below sp, even temporarily).
Same apply to

chacha-opt/app/extensions/chacha/chacha_neon-32.inc

Line 829 in d69e5ac

stmia sp!, {r4-r7}