Date: Wed, 3 Feb 2010 16:03:12 +0200 From: Andrey Simonenko <simon@comsys.ntu-kpi.kiev.ua> To: Stefan Midjich <swehack@gmail.com> Cc: freebsd-hackers@freebsd.org Subject: Re: Does getc(3) use the read(2) syscall? Message-ID: <20100203140312.GA34290@pm513-1.comsys.ntu-kpi.kiev.ua> In-Reply-To: <e0e25d5e1002030326p5e0ef0a1q5ebc77a4e1c69b7c@mail.gmail.com> References: <e0e25d5e1002030326p5e0ef0a1q5ebc77a4e1c69b7c@mail.gmail.com>
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Hello, On Wed, Feb 03, 2010 at 12:26:02PM +0100, Stefan Midjich wrote: > I'm having trouble looking this function up in the source tree, the trail > seems to end at __sys_read which has a bunch of prototypes but i can't find > the actual function code. > > So my question is primarily, does getc use the read system call eventually? The easiest way is to write a simple program with this function and run it under ktrace and verify all calls in the output of kdump. > > But i would also love it if someone could show me where __sys_read is > defined. Quick check of the path gave me the following: getc -> __sgetc -> __srget -> __srefill -> _sread -> [._read ] -> __sread -> _read Look how Assembler files for system calls invocations are generated in the lib/libc/sys/Makefile.inc file, and look at macro variables defined in the amd64/SYS.h file. If you understand the idea, then check read.S file in the <obj>/lib/libc/ directory and the output of "nm read.So". Declaration of _read() in libc/stdio/stdio.c is done by a trick with two header files namespace.h included before and un-namespace.h included after another header files. Looks like that __sys_read in libc/ is used in directories with thread code and prototype for __sys_read is defined there.
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