Messages in this thread | | | Date | Wed, 25 Jun 2008 08:53:10 -0400 (EDT) | From | Mikulas Patocka <> | Subject | Re: [10 PATCHES] inline functions to avoid stack overflow |
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On Wed, 25 Jun 2008, Helge Hafting wrote:
> Mikulas Patocka wrote: >> Hi >> >> Here I'm sending 10 patches to inline various functions. >> >> To give you some understanding of sparc64, every function there uses big >> stack frame (at least 192 bytes). 128 bytes are required by architecture >> (16 64-bit registers), 48 bytes are there due to mistake of Sparc64 ABI >> designers (calling function has to allocate 48 bytes for called function) >> and 16 bytes are some dubious padding. > I guess there is no way around those 128 bytes required by hardware - but > is it necessary to allocate the 48 bytes of "mistake" and the dubious > padding? > > Linux kernel functions don't call any outside functions, and are not called > from > outside either. So violating the ABI should be ok - there is nothing else to > be compatible to. Similiar to how x86 experimented with --mregparm to get > a little more performance from changing the kernel calling convention. > Helge Hafting
So, ask gcc developers to do kernel-specific ABI with only 128-byte stack frame.
BTW. could some gcc developer explain the reason for additional 16-bytes on stack on sparc64? 64-bit ABI mandates 176 bytes, but gcc allocates 192 bytes.
Even worse, gcc doesn't use these additional bytes. If you try this:
extern void f(int *i); void g() { int a; f(&a); }
, it allocates additional 16 bytes for the variable "a" (so there's total 208 bytes), even though it could place the variable into 48-byte ABI-mandated area that it inherited from the caller or into it's own 16-byte padding that it made when calling "f".
Mikulas
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