From: Florian Weimer <fweimer@redhat.com>
To: Will Hawkins <whh8b@virginia.edu>, libc-help@sourceware.org
Subject: Re: Question about the highly optimized aspects of libc implementation
Date: Thu, 30 Nov 2017 08:36:00 -0000 [thread overview]
Message-ID: <fde62ca9-cc75-d065-3ab3-25b627e0f12d@redhat.com> (raw)
In-Reply-To: <CAE+MWFsT5vu4yW0zDKgyinZky=2s-i2wzK7N-fnKuQP0kGQ_Bw@mail.gmail.com>
On 11/30/2017 07:47 AM, Will Hawkins wrote:
> I've been digging through the glibc implementation and looking for
> examples of where compiler directives or hand-written assembly have
> been used to improve performance at the "expense" of standards or
> conventions.
The fcntl implementation calls va_arg on a variadic argument which might
not actually exist. The syscall function does something similar (but it
is actually implemented in machine code, so it's less of a problem).
The NSS internals in general and getaddrinfo in particular call
functions through a mis-matching function pointer (with an additional
argument added, or with a void * argument where the function is defined
with a concrete function pointer).
Calling functions such as getpwuid_r with a pointer which has not been
allocated on the heap (or reusing an existing allocation for a second
call) is probably not quite valid C due to aliasing violations.
A lot of the code which manipulates struct
sockaddr/sockaddr_in/sockaddr_in6 objects does not make the additional
copies which are needed to avoid aliasing violations.
Do you need more? I can probably go on for quite some time.
Thanks,
Florian
next prev parent reply other threads:[~2017-11-30 8:36 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-11-30 6:48 Will Hawkins
2017-11-30 6:54 ` Siddhesh Poyarekar
2017-11-30 8:22 ` Florian Weimer
2017-11-30 6:56 ` Carlos O'Donell
2017-11-30 7:00 ` Will Hawkins
2017-11-30 8:36 ` Florian Weimer [this message]
2017-12-04 1:15 ` Will Hawkins
2017-12-04 8:12 ` Siddhesh Poyarekar
2017-12-04 12:15 ` Florian Weimer
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