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Re: Question about the highly optimized aspects of libc implementation

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

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.


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