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Full Discussion: A question regarding the gcc compiler ...
Top Forums Programming A question regarding the gcc compiler ... Post 302476289 by Corona688 on Wednesday 1st of December 2010 10:30:04 AM
Old 12-01-2010
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...
This User Gave Thanks to Corona688 For This Post:
Praveen_218
 

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LEARN ABOUT DEBIAN

cxref-cpp

cxref-cpp(1)						      General Commands Manual						      cxref-cpp(1)

NAME

       cxref-cpp - A modified C preprocessor to use with cxref.

SYNOPSIS

       cxref-cpp ...

DESCRIPTION

       To  improve  the  output  that  is available for the source code for cross-referencing a modified version of the GNU CPP v2.7.2 is supplied
       (named cxref-cpp).

       This modified C preprocessor allows for a finer control over some features of the preprocessing that are not important for a compiler.	In
       a  standard  preprocessor, the preprocessor directives are intended for use only by the preprocessor, so passing the information through is
       not important.

       With cxref-cpp, there are some features that are different to the standard GNU CPP:

	      Compared to gcc versions earlier than version 2.8.0 there is an extra option that will output the #include  lines  from  the  source
	      file.  In version 2.8.0 and later this option is present.

	      Comments	trailing  a  #include  or  a  #define are not preserved by all versions of gcc even if the -C option is used.  This is not
	      important while compiling, but is useful for documenting.

	      The cxref-cpp program will take on the personality of the installed version of gcc so that the gcc header files can be parsed.  This
	      means  that it includes the same default include directory paths and macro definitions.  The file that contains these definitions is
	      called cxref-cpp.defines and is installed by the cxref-cpp-configure program or specified by  the  -cxref-cpp-defines  command  line
	      option.

OPTIONS

       The same as for gcc, apart from '-cxref-cpp-defines' described above.

SEE ALSO

       cxref(1), cxref-cpp-configure(1), gcc(1)

								    May 9, 2004 						      cxref-cpp(1)
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