Re: [PATCH] vsprintf.c: Reduce sizeof struct printf_spec from 24 to8 bytes

From: Linus Torvalds
Date: Sat Mar 06 2010 - 21:25:39 EST

On Sat, 6 Mar 2010, Linus Torvalds wrote:

> the 'pointer()' function has a 200+ byte stack footprint on x86-64. And
> vsnprintf itself is about 100+ bytes. So that stack depth is way bigger
> than I would have expected.
> I'm not sure _why_ that stack footprint for 'pointer()' is so big, but I
> bet it's due to some simple inlining, and gcc (once more) sucking at it
> and not being able to combine stack frames. It's a damn shame.

Yeah, a few noinline's gets 'pointer()' to just save registers on the
stack, no need for any extra buffers (which then is ok for your recursion
case - the other subfunctions it can call have their own buffers, of
course, but they won't be in the recursive call-path except at the leaf.

vsnprintf() itself seems less obviously fixable. I'm not sure wht gcc
decides it needs 88 bytes of temp-space there.

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