gcc vs clang: why do you stay or switch?

CaptainBlood · Advocate Joined: 24 Jan 2010 Posts: 3952

More and more topics have clang as an origin of issue.
Likely only because more and more users are switching. no judging on clang here.

I've just noticed stage3 has a LLVM version.

LTO kernel requires clang as gcc in this respect is simply not there.

IIUC clang is expected to compile faster in many cases which would be a time-saver when testing source packages or ebuilds.

As far as performance is concerned I know there are packages which do perform much faster when build with clang.
Defining such a list isn't a easy task.

There can be other reasons, unlisted there. :roll:

Anyone having switched at package level or globally to share reasons of choice, whatever their stage3 was?

Thks 4 ur attention, interest & support.
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Zucca · Posted: Sun Dec 01, 2024 11:19 am Post subject:

I've used musl+llvm toolchain on amd64. And I'm about to set up one once again. Last time I ran it, it needed some extra work with some of the packages. And I needed to mask gcc.
I do run (not updated recently) glibc+llvm on my MacBook Air M2 which is arm64 obviously. I have hopes llvm could give better optimizations on Apple ARM since Apple itself uses llvm quite a lot. There hasn't been problems, but I don't use it very much because of the lack of memory (only 8G with no possibility to upgrade).
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Goverp · Advocate Joined: 07 Mar 2007 Posts: 2183

I switched to Clang 'cos it uses less space to compile qtwebengine, and hence can compile it faster. Having done that for qtwebengine, I thought I'd try it on more and more stuff until now it's my default*. My reason for that is Clang & LLVM are much newer than gcc, and (as Captain Blood mentioned, works better with LTO), and I assume large software suffers with age.
Also, AFAIK the only way to compile a kernel with LTO is with Clang.

* I say "default", as I have a package.env file for those where Clang breaks, but I know that the Gentoo devs also override the use of Clang for packages they know are broken, so I probably use Clang rather less often than I think!
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CaptainBlood · Advocate Joined: 24 Jan 2010 Posts: 3952

Spanik · Veteran Joined: 12 Dec 2003 Posts: 1006 Location: Belgium

I have a couple of packages that I use clang because when compiling them with gcc I hit a hardware issue with the cpu (AMD Epyc). So more a workaround then anything else.
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mirekm · Posted: Mon Dec 02, 2024 9:12 am Post subject:

I stay on gcc. The main reason is security. For gcc there is hardened version.
The other thing is that clang allow bad quality code to work, and you will never know where is a hole allowing attack to your computer.

Hu · Administrator Joined: 06 Mar 2007 Posts: 22768

Both gcc and clang allow bad quality code to compile, as long as the code is standards-compliant. It is fairly straightforward to write a program that both compilers will accept, but that has serious security problems when exposed to untrusted input. Therefore, I think it is not fair to blame clang for allowing bad quality code to work.

CaptainBlood · Advocate Joined: 24 Jan 2010 Posts: 3952

mirekm · Posted: Tue Dec 03, 2024 6:25 am Post subject:

mirekm · Posted: Tue Dec 03, 2024 6:30 am Post subject:

[quote]So IIUC ebuild hardened kernel is currently gcc only, right?
/quote]

This I don't know. I didn't try to compile kernel with clang. As far I remember, on newest kernels there were patches to compile it with clang.

bstaletic · Guru Joined: 05 Apr 2014 Posts: 382

CaptainBlood · Advocate Joined: 24 Jan 2010 Posts: 3952

Hu · Administrator Joined: 06 Mar 2007 Posts: 22768

To extend on bstaletic's response to mirekm's comments about Chromium, I would add that if gcc is rejecting these files, and clang is accepting them, then it seems more likely that gcc is being strict about requiring correct inputs and clang is being sloppy and allowing invalid inputs. However, mirekm's earlier post read to me more like a complaint that clang was allowing insecure code to succeed. There is an important distinction between code which is unsafe to run because it may do something bad versus code that is safe to run, but painful to read and compile. Assuming mirekm's comments about Chromium are accurate, we know only that some unspecified version is painful to compile. It might be perfectly safe and secure to run once it is compiled. Without a specific version and specific error messages, we cannot determine the true extent of the problems with Chromium.