Time to debug those CFLAGS people

Message

hensan · Post by **hensan** » Thu Oct 30, 2003 12:40 pm

I just saw on the gentoo portage stats page that some 3% of the people who have posted their clags there use -03 (zero three, wrong) instead of -O3 (big O three, right) in their CFLAGS, thereby making it the 20th most popular flag.

frippz · Post by **frippz** » Thu Oct 30, 2003 1:30 pm

Oh dear...
Those poor people!

guy · Post by **guy** » Thu Oct 30, 2003 1:42 pm

*Levi* wrote:Oh dear...
Those poor people!

I definitely did that my first install but was to ashamed to mention it

Moofed · Post by **Moofed** » Thu Oct 30, 2003 1:45 pm

And only ~55% use -pipe?! Is there a reason to not use -pipe?

Andersson · Post by **Andersson** » Thu Oct 30, 2003 5:55 pm

That is because many people don't bother setting the cflags at all.

TPC · Post by **TPC** » Thu Oct 30, 2003 6:36 pm

10% use -march=pentium4? I thought that was broken? is it fixed?

Zeitgeist · Post by **Zeitgeist** » Thu Oct 30, 2003 7:43 pm

-O2 is faster anyway...

Xaignar · Post by **Xaignar** » Thu Oct 30, 2003 7:57 pm

TPC wrote:10% use -march=pentium4? I thought that was broken? is it fixed?

It's fixed in the newer versions of gcc.

Evangelion · Post by **Evangelion** » Thu Oct 30, 2003 8:12 pm

If you are interested in optimizations, then I suggest that you read this

Athas · Post by **Athas** » Thu Oct 30, 2003 8:35 pm

Another thing I wonder about, is why more people put "gtk2" in their USE-flags than "X"

so · Post by so » Thu Oct 30, 2003 9:52 pm

Athas wrote:Another thing I wonder about, is why more people put "gtk2" in their USE-flags than "X"

me too

thrasher6670 · Post by **thrasher6670** » Fri Oct 31, 2003 2:55 am

so wrote:
Athas wrote:Another thing I wonder about, is why more people put "gtk2" in their USE-flags than "X"
me too

Well is is implied if not specifically specified

.

wow, people talking about my site. cool.
anything else people would like to see in the stats?

QPegasus · Post by **QPegasus** » Fri Oct 31, 2003 3:43 am

Andersson wrote:That is because many people don't bother setting the cflags at all.

Isnt -pipe enabled by default, along with -O3 and whatever processor you have?

Although, I guess a lot of people update portage, etc-update, wipe their old make.conf and dont bother transferring over their CFLAGS/USE settings.

I can understand if many people dont care about such things though, and just use Gentoo because of the number of packages in portage.

zez · Post by **zez** » Fri Oct 31, 2003 4:20 am

Athas wrote:Another thing I wonder about, is why more people put "gtk2" in their USE-flags than "X"

Actually X is listed in make.defaults so it should be on by default, right?

meowsqueak · Post by **meowsqueak** » Fri Oct 31, 2003 6:15 am

Yeah, the stats script isn't smart enough to consider those USE flags on by default. I could probably make it do that, but it depends on what the statistics are actually trying to convey...

CheshireCat · Post by **CheshireCat** » Fri Oct 31, 2003 8:15 am

dlpierce wrote:
And only ~55% use -pipe?! Is there a reason to not use -pipe?

-pipe can be slower. I believe this depends on kernel version, and probably on the code being compiled, but pipes can be slower than small temp files, which will often never get written to disk at all.

thrasher6670 · Post by **thrasher6670** » Sat Nov 01, 2003 5:54 am

i changed the script slightly, it was including people that had not set any useflags/cflags

should be more accurrate now.

Chickpea · Post by **Chickpea** » Sat Nov 01, 2003 7:11 am

Andersson wrote:That is because many people don't bother setting the cflags at all.

Maybe because we dont understand what they do....at least in my case that is. I have only recently started using them

slarti` · Post by **slarti`** » Sat Nov 01, 2003 11:35 am

I really need to tidy my CFLAGS up. They work well, but I repeat myself quite a lot...

Code: Select all

CFLAGS="-march=athlon-xp -mmmx -msse -m3dnow -Os -pipe -fomit-frame-pointer -fforce-addr -fprefetch-loop-arrays -falign-functions=16 -falign-labels=1 -falign-loops=16 -falign-jumps=16 -fstack-protector -mfpmath=sse,387"

I think most of the -m*'s are implied by -march anyway, so I can probably get rid of those.

How many of these flags are already implied?

hensan · Post by **hensan** » Sat Nov 01, 2003 1:25 pm

sonic_ wrote:How many of these flags are already implied?

-mmmx, -msse and -m3dnow are implied by your -march

Also I see you use -Os, nothing wrong with that. But since you then explicitly enable all the flags that makes -Os different from -O2 (except -freorder-blocks), you might as well use -O2 and remove -falign-functions, -falign-jumps, -falign-loops, -falign-labels, -freorder-blocks and -fprefetch-loop-arrays. These flags have quite good values by default, so you don't really gain much by defining your own values.

I couldn't find -fstack-protector in the gcc documentation, whats that all about?

Azaghal · Post by **Azaghal** » Sat Nov 01, 2003 1:37 pm

I've yet to notice a difference between different CFLAGS...

And no, I don't use -03

Stu_28 · Post by **Stu_28** » Sat Nov 01, 2003 1:55 pm

hensan wrote:
sonic_ wrote:How many of these flags are already implied?
-mmmx, -msse and -m3dnow are implied by your -march

Also I see you use -Os, nothing wrong with that. But since you then explicitly enable all the flags that makes -Os different from -O2 (except -freorder-blocks), you might as well use -O2 and remove -falign-functions, -falign-jumps, -falign-loops, -falign-labels, -freorder-blocks and -fprefetch-loop-arrays. These flags have quite good values by default, so you don't really gain much by defining your own values.

I couldn't find -fstack-protector in the gcc documentation, whats that all about?

You missed -fomit-frame-pointer, it's in all the O's. And the -fstack-protector is ProPolice ( http://www.research.ibm.com/trl/projects/security/ssp/ ).

hensan · Post by **hensan** » Sat Nov 01, 2003 2:39 pm

From the GCC manual:

-O also turns on -fomit-frame-pointer on machines where doing so does not interfere with debugging.

x86 processors need the frame pointer for debugging, so -fomit-frame-pointer is not turned on by default.

fp2099 · Post by **fp2099** » Thu Nov 06, 2003 11:11 pm

I actually use different flags for different things...
i used make.conf.stable to system and make.conf.optimum to world
make.conf.stable has
-mcpu=athlon-tbird -O2 -fomit-frame-pointer
and the other has
-march=athlon-tbird -O3 -pipe pipe-fforce-addr -fomit-frame-pointer -funroll-loops -falign-functions=4 -maccumulate-outgoing-args

At the time this seemed to be a smart move... now... er...

curtis119 · Post by **curtis119** » Sat Nov 08, 2003 8:36 pm

I just wanted to say thank you for making the gentoo-portage website. It is a great resource and is a REAL improvement over the basic online portage database at gentoo.org. I hope that the developers (or the web-admin - whoever makes those decisions) will integrate it into gentoo.org. (hint hint).

Again Thanks for the great work!!

ps. I have tried a lot of different cflag combinations and the one that seems to give the best performance overall is "-march=pentium4 -Os -pipe -fomit-frame-pointer -msse2" It gives the fastest startup times to Gnome, the least amount of app crashes and everything just seems to run smoother (subjectivly speaking).

One of the things I noticed about using "-fexpensive-optimizations" is that Nautilus crashes when I delete something with the right-click menu, no matter what other flags are used.

Time to debug those CFLAGS people

Time to debug those CFLAGS people

errr...