Bug 431154

Summary:	Kernel Sources Compile Flags
Product:	Gentoo Linux	Reporter:	Jeffrey Walton <noloader>
Component:	[OLD] Core system	Assignee:	Gentoo Linux bug wranglers <bug-wranglers>
Status:	RESOLVED WORKSFORME
Severity:	QA
Priority:	Normal
Version:	unspecified
Hardware:	AMD64
OS:	OS X
Whiteboard:
Package list:		Runtime testing required:	---

Description Jeffrey Walton 2012-08-12 23:23:00 UTC

I'm working through a Gentoo installation. I'm at Chapter 7 and 'emerge gentoo-sources' (almost there).

I see -Wall and -Wextra are being used (sample below). That's awesome - I don't ever recall seeing it in the free software world. Hats off to the folks responsible for getting the option added.

CCCMD = x86_64-pc-linux-gnu-gcc -DPERL_CORE -c -fno-strict-aliasing -pipe -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64  -std=c89 -O2 -pipe  -Wall -ansi -W -Wextra -Wdeclaration-after-statement -Wendif-labels -Wc++-compat 
`sh  cflags "optimize='-O2 -pipe'" reentr.o` -fPIC reentr.c

I noticed a couple of interesting options are not present that might be useful: -Wconversion, and -fstrict-overflow -Wstrict-overflow. I don't believe they are part of -Wall and -Wextra.

I like to use the above flags to catch problems lurking in the background, such as truncation and extension problems, and code removed due to optimizations. They are especially important on a 64-bit machine, where the developer only used a 32-bit machine for dev/qa.

Comment 1 Jeffrey Walton 2012-08-12 23:27:17 UTC

$ uname -a
Linux Gentoo-2012 3.3.0-gentoo-r1 #1 SMP Fri Mar 30 06:21:40 UTC 2012 x86_64 Intel(R) Core(TM) i7-2760QM CPU @ 2.40GHz GenuineIntel GNU/Linux

Inside a VM om Mac OS X.

Comment 2 Jeroen Roovers (RETIRED) gentoo-dev

2012-08-13 13:23:54 UTC

We didn't add these. They are upstream defaults. We strive to add ours (CFLAGS and so on) after the upstream ones to allow Gentoo users more control over them. We also strive to remove upstream CFLAGS that might clash with our CFLAGS (or lack thereof), like overzealous optimisation and architecture specific options.

You can add the compiler flags you like to the CFLAGS variable in your own make.conf, though.

Comment 3 Jeroen Roovers (RETIRED) gentoo-dev

2012-08-13 13:24:42 UTC

(In reply to comment #2)
> We didn't add these. They are upstream defaults.

In the example you presented, they are from dev-lang/perl. :)