A question regarding the gcc compiler ... Post: 302476289

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Top Forums Programming A question regarding the gcc compiler ... Post 302476289 by Corona688 on Wednesday 1st of December 2010 10:30:04 AM

12-01-2010

Registered User

So, you're trawling the entire /usr/lib/ directory? by default gcc uses these and only these:

Code:

# Compiling with -static to make it more obvious which things it uses
$ echo "main() { return(42); }" > 42.c
$ strace -f gcc -static 42.c -o 42 2> 42.log
$  grep "\.[ao]" 42.log | grep open | egrep -v "ENOENT|/tmp"
[pid  7741] open("/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/../../../crt1.o", O_RDONLY|O_LARGEFILE) = 4
[pid  7741] open("/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/../../../crti.o", O_RDONLY|O_LARGEFILE) = 5
[pid  7741] open("/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/crtbeginT.o", O_RDONLY|O_LARGEFILE) = 6
[pid  7741] open("/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/libgcc.a", O_RDONLY|O_LARGEFILE) = 8
[pid  7741] open("/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/libgcc_eh.a", O_RDONLY|O_LARGEFILE) = 9
[pid  7741] open("/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/../../../libc.a", O_RDONLY|O_LARGEFILE) = 10
[pid  7741] open("/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/crtend.o", O_RDONLY|O_LARGEFILE) = 11
[pid  7741] open("/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/../../../crtn.o", O_RDONLY|O_LARGEFILE) = 12

Try a library it'll have to look for, like pthread:

Code:

# Yes, I'm aware the code is nonsense.  Nothing better's needed
$ echo "main() { return(pthread_create(42)); }" > 42.c
$ gcc 42.c
/tmp/cckAe1dw.o: In function `main':
42.c:(.text+0x19): undefined reference to `pthread_create'
collect2: ld returned 1 exit status

...It didn't find it. gcc only looks inside what it's told to look inside -- by default a very small set of libraries encompassing stdio, libc, a few math builtins, that's it. It has to be explicitly told to check in libpthread.so (or libpthread.a when linking statically) like

Code:

$ gcc -lpthread 42.c
$

So gcc never had any special superfast linker finding thing. It's just been told where to look. When you start linking in dozens of libraries, you'll indeed find gcc having to do a lot more work...

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LEARN ABOUT DEBIAN

sitepods

SITEPODS(1p)						User Contributed Perl Documentation					      SITEPODS(1p)

NAME

       sitepods - print out the paths to the modules that this site added

DESCRIPTION

       This program shows the paths to module pods that are in the site_perl directories.

EXAMPLES

	   $ sitepods
	   /usr/local/devperl/lib/site_perl/5.00554/i686-linux/XML/Parser/Expat.pm
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       You can also run this using alternate perl binaries, like so:

	   $ oldperl -S sitepods
	   ....

SEE ALSO

       faqpods(1), modpods(1), pods(1), podpath(1), and stdpod(1).

AUTHORS and COPYRIGHTS
       Copyright (C) 1999 Tom Christiansen.

       Copyright (C) 2006-2008 Mark Leighton Fisher.

       This is free software; you can redistribute it and/or modify it under the terms of either: (a) the GNU General Public License as published
       by the Free Software Foundation; either version 1, or (at your option) any later version, or (b) the Perl "Artistic License".  (This is the
       Perl 5 licensing scheme.)

       Please note this is a change from the original pmtools-1.00 (still available on CPAN), as pmtools-1.00 were licensed only under the Perl
       "Artistic License".

perl v5.10.1							    2010-02-22							      SITEPODS(1p)

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