Conditional makefile: help

This is a discussion on Conditional makefile: help within the Tech Board forums, part of the Community Boards category; Hello everybody! I hope somebody could help me to solve this iussue: I should create a makefile which, according to ...

  1. #1
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    Conditional makefile: help

    Hello everybody!
    I hope somebody could help me to solve this iussue: I should create a makefile which, according to the gcc version installed on the machine where the make will be run, will set or not the flag "-fno-stack-protector" (for gcc versions < 4.1, this flag doesn't exist since SSP is not present in gcc and i would get an error).
    How could I do such a makefile?
    Thanks in advance!
    Bye!

  2. #2
    and the hat of int overfl Salem's Avatar
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    Collect the output of `gcc -v`, then use something to extract the version number.
    Use that as the basis of your decision.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
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  3. #3
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    Quote Originally Posted by Salem View Post
    Collect the output of `gcc -v`, then use something to extract the version number.
    Use that as the basis of your decision.
    hello! 1st of all, thanks for answering!
    my problem is exactly how to parse the result of gcc -v and decide for the flags in a makefile... I am not really experienced with makefiles... Any hints?
    Thanks again!

  4. #4
    Captain Crash brewbuck's Avatar
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    Quote Originally Posted by smoking81 View Post
    hello! 1st of all, thanks for answering!
    my problem is exactly how to parse the result of gcc -v and decide for the flags in a makefile... I am not really experienced with makefiles... Any hints?
    Thanks again!
    The "gcc --version" command sucks, because the format of its output changes from version to version. Instead, check to see if gcc actually supports the option:

    Code:
    -include .cflags
    CFLAGS  = $(STACK_FLAGS) -W -Wall
    
    all:
            echo My CFLAGS is $(CFLAGS)
    
    .cflags:
            gcc -c -fno-stack-protector check.c
            echo "STACK_FLAGS=-fno-stack-protector" > .cflags
    We trigger a failure-protected inclusion of .cflags. This file has a rule which calls gcc on a dummy file with the flag to be checked. If this call succeeds, the next command in the .cflags rule runs, which creates a mini-makefile containing a variable STACK_FLAGS with the appropriate option. If, on the other hand, gcc does not support the option, processing of the .cflags rule aborts and the .cflags file does not get created, thus the flag does not get set.

    I included an "all" target so you can test if it works.

  5. #5
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    There is a piece of version checking code for gcc in this:
    http://lxr.xensource.com/lxr/source/Config.mk

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