Stack usage (in gv_stashpvn and others)

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Moin,

once again in gv_stashpvn:

Perl_gv_stashpvn(pTHX_ const char *name, U32 namelen, I32 create)
{
    char smallbuf[256];
    char *tmpbuf;
    HV *stash;
    GV *tmpgv;

The intention is good, a small buffer on the stack is used to avoid a 
malloc/free. The coverage http://www.maddingue.net/perlcover/--gv-c.html 
says the larger buffer is only needed 6 times.

However, I wonder whether the buffer couldn't be shrunk a bit. 256 Bytes 
is quite a bit, on systems with small stacks ( 8 or 4 Kbyte), this will 
stress the stack. Especially because stashpvn calls fetchpvn_flags, which 
also contains a 256 Byte stack buffer (around line 764), meaning whoever 
calls gv_stashpvn needs to have about 550 byte left on the stack, or bad 
things will happen.

(I am not sure how the compiler will allocate the buffer in 
gv_fetchpvn_flags because it is in a loop in the inside, but it will 
probably use the worst case and always allocate it once from the stack)

So, I propose to change the buffers to [128], that should suffice for the 
normal usage case, and shrink the stack usage a bit.

It would be good if we could find out how much stack each function uses, I 
know the linux kernel developers looked at this data to put stack usage 
on a diet.

Comments?

Best wishes,

Tels

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• Stack usage (in gv_stashpvn and others) by Tels
• Re: Stack usage (in gv_stashpvn and others) by Tels
• Re: Stack usage (in gv_stashpvn and others) by Rafael Garcia-Suarez