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Message-ID: <20150525143503.GC20259@port70.net>
Date: Mon, 25 May 2015 16:35:04 +0200
From: Szabolcs Nagy <nsz@...t70.net>
To: musl@...ts.openwall.com
Subject: Re: ppc soft-float regression
* Alexander Monakov <amonakov@...ras.ru> [2015-05-25 16:40:46 +0300]:
> >
> > currently a libc call always uses less than 10K stack(*)
> > but the guaranteed limit is not documented (16K limit is
> > fine i guess).
>
> Not true: fmt_fp consumes more that LDBL_MAX_EXP bytes, which is 16384 on x86
> and aarch64. As I recall, there's another function with >16K static stack
> usage in the resolver, but I forget where exactly.
note the /9
uint32_t big[(LDBL_MANT_DIG+28)/29 + 1 // mantissa expansion
+ (LDBL_MAX_EXP+LDBL_MANT_DIG+28+8)/9]; // exponent expansion
you can compile musl with -fstack-usage and analyze
the output (i did that once on i386) and verify that
all stack usage is <10K (some functions have vla or
recursion where verification is harder)
(the large worst-case stack users are printf, scanf,
glob, execl, the dynamic loader does not use that much
stack: it keeps some file names and elf header in buffers
but it should use < 3K).
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