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Linux From Scratch This Forum is for the discussion of LFS.
LFS is a project that provides you with the steps necessary to build your own custom Linux system.


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Old 07-08-2003, 12:53 AM   #1
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binutils: from the book 4.1

There is something stated regarding binutils which goes like this:
This package is known to behave badly when you have changed its default optimization flags (including the -march and -mcpu options). Therefore, if you have defined any environment variables that override default optimizations, such as CFLAGS and CXXFLAGS, we recommend unsetting or modifying them when building binutils.
I'm having problems compiling binutils, I can't recall the error right now because I'm at work.

But can someone explain to me what CFLAGS and CXXFLAGS are and how do I go about unsetting their default values (and setting them back again after successfully compiling binutils)?

Thanks in advance.
Old 07-08-2003, 01:23 PM   #2
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I'm afraid I don't know what CFLAGS and CXXFLAGS control except that they influence how a package is compiled.

You can find out what they contain just like any other environment variable. Just type:
echo $CFLAGS

If you don't get any output or get an 'undefined' message, they aren't set to anything. If they do have something in them, then write it down. To remove their contents, type:

After you compile, you can put them back by typing this:
export CFLAGS=old_cflags_value
export CXXFLAGS=old_cxxflags_value

What's the text of the error you're getting?
Old 07-08-2003, 11:03 PM   #3
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Those flags are used to supply additional options to the compilers pre-processor linker etc.

CFLAGS is used by the c compiler
CXXFLAGS is used by the c++ compiler
LDFLAGS are passed to the linker
CPPFLAGS are passed to the c preprocessor

Anything set in these environment variables will be added to the gcc command line during compilation.

Best check the gcc doco for the myriad of options you can use.

Most common for CFLAGS/CXXFLAGS is specifying an optimisation level ( -O2 ), forcing gcc to comunicate via a pipe instead of creating files ( -pipe ) setting architecture ( -march=blah ) setting cpu ( -mcpu=blah ) specifying locations to search for headers ( -I/opt/include )

LDFLAGS is used to pass options when the linker is invoked, commonly used are stripping debugging symbols ( -s ), compiling statically ( -static ) and many many more.

Binutils CFLAGS ARE best left alone, but you are pretty safe if you only use CFLAGS="-O2 -pipe"

Most likely you won't have any CFLAGS etc set in your environment anyway if you have a relatively standard .profile/.bash_profile/.cshrc
Old 07-09-2003, 09:53 PM   #4
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Thanks guys... anyway, I restarted from my LFS attempt again. But again, I'm thankful that you explained to me the meaning of these flags.

Much appreciated.

So far everything is working out much better than my first attempt.


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