Question

I am running on a CentOS 5.7 system.

I downloaded a source package and a .spec file from someone else. I am trying to build a RPM from the source using a vanilla command like:

% rpmbuild -ba ~/rpmbuild/SPECS/foo.spec
...
Configuration summary:
======================

  Host type................: x86_64-redhat-linux-gnu
  CC.......................: gcc
  CFLAGS...................: -O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector --param=ssp-buffer-size=4 -m64 -mtune=generic -Werror

  Package..................: sudosh2
  Version..................: 1.0.4

  Installation prefix......: /usr
  Man directory............: /usr/share/man
  sysconfdir...............: /etc
  recording input..........: no

However, this build is failing. The code is a little sloppy and is generating some warnings. Some part of this toolchain is enabling -Werror flag, which makes “all warnings into errors.” Thus, the build fails with an error:

gcc -DHAVE_CONFIG_H -I. -I..     -O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector --param=ssp-buffer-size=4 -m64 -mtune=generic -Werror -MT parse.o -MD -MP -MF .deps/parse.Tpo -c -o parse.o parse.c
cc1: warnings being treated as errors
sudosh.c: In function 'main':
sudosh.c:486: warning: unused variable 'written'
sudosh.c:112: warning: unused variable 'found'
cc1: warnings being treated as errors
parse.c: In function 'parse':
parse.c:20: warning: unused variable 'y'
parse.c:14: warning: unused variable 'opt'
parse.c:14: warning: unused variable 'cmt'
parse.c:14: warning: unused variable 'arg'
parse.c:10: warning: unused variable 'i'
parse.c:10: warning: unused variable 'line_number'
make[2]: *** [sudosh.o] Error 1

I know the proper fix is for the author to fix the code, but I want to work around this problem in the short term. I need a working RPM.

It looks like either ./configure or autoconf is automatically adding the -Werror flag. How can I disable the -Werror flags for my builds, short of editing the Makefile myself?

Update in response to @pwan’s answer:

The .spec file is pretty generic, and doesn’t specify any special flags:

%build
%configure \
    --program-prefix="%{?_program_prefix}"
%{__make} %{?_smp_mflags}

Answer 1

How can I disable the -Werror flags for my builds, short of editing
the Makefile myself?

The GCC manual has the solution in 3.8 Options to Request or Suppress Warnings:

You can request many specific warnings with options beginning -W',
for example -Wimplicit to request warnings on implicit declarations.
Each of these specific warning options also has a negative form
beginning-Wno-‘ to turn off warnings; for example, -Wno-implicit.
This manual lists only one of the two forms, whichever is not the
default.

So, setting -Wno-error the CFLAGS environment variable did the trick for me. Now that I know what I’m looking for, I can see that Stackoverflow has a wealth of answers: https://stackoverflow.com/search?q=%22-Wno-%22 , specifically how to disable specific warning when -Wall is enabled.

In my specific case, the build was failing due to ‘warning: unused variable”, and I can suppress those specific warnings with -Wno-unused-variable.

Since I’m using rpmbuild, I need to put this in the .spec file as suggested by @pwan. The only way I could figure this out was to:

1. Build the rpm once:

   rpmbuild -v -bb ~/rpmbuild/SPECS/sudosh.spec
   

2. Search for the CFLAGS which is generated by ./configure

   Configuration summary:
   ======================
   
     Host type................: x86_64-redhat-linux-gnu
     CC.......................: gcc
     CFLAGS...................: -O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector --param=ssp-buffer-size=4 -m64 -mtune=generic -Werror
   

3. And manually append these CFLAGS to my .spec file, into the `%configure% section:

   %configure \
       --program-prefix="%{?_program_prefix}"
   #%{__make} %{?_smp_mflags}
   %{__make} %{?_smp_mflags} CFLAGS="-O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector --param=ssp-buffer-size=4 -m64 -mtune=generic -Werror -pedantic-errors -Wno-unused-variable -ansi -std=c99"
   

The above is a little hack-ish, because if the ./configure script is changed upstream I may need to re-adjust the CFLAGS in my .spec file.