clang vs gcc 2020

Provide clear diagnostic messages. in clang were known or not when the decision was made. Command Tips ; 1. It's not a guideline so I'm not bothered by the wording. Do you have a src.rpm where you enable the clang LTO and PGO? libc++ is the library used by clang for c++. I'd like to get an exception to use clang until gcc is fixed. But it is not enough to generalize to other programs or the whole distro. ac_add_options --enable-tests You can directly compare fedora firefox builds with binaries provided by mozilla. I wonder if gcc team is able to provide gcc fixes needed to build Firefox, that's the main point here. Clang vs. GCC - code coverage checking April 2, 2016. @kkofler There's a clear benchmark in this particular case. The problem is that this is not what we need compared, which is Firefox Fedora binaries built with GCC vs. built with Clang. The one such reason that was brought forward turned out to be false. GCC 4.9.0 Clang 3.5.0 benchmarks, GCC 4.9.0 Clang 3.5.0 performance data from OpenBenchmarking.org and the Phoronix Test Suite. (https://bugzilla.mozilla.org/show_bug.cgi?id=1495742). Closing since the gcc bug was fixed and firefox is still built with gcc. It seems strange that the C/C++ guidelines wouldn't mention this. The system compiler (gcc) makes sure they We're a place where coders share, stay up-to-date and grow their careers. faster binaries. The guidelines don't seem to offer any wiggle room here: "Packages may only build with an alternative compiler to gcc if upstream does not support gcc.". AST generated by clang is easily understandable. At least until Mozilla moves the tests from gcc-plugin they need to support it. qemu is much slower when built with clang vs gcc, Brian Cain, 2020/08/24 qemu is much slower when built with clang vs gcc , Taylor Simpson <= Prev by Date: … On the library front, MSVC implements and releases new features at about the same rate as GCC and Clang. We don't even have gcc in the buildroot by default these days. Mozilla upstream switches from gcc to clang and we're going to follow upstream here due to clang performance, maintenance costs and compilation speed. Similar to how GCC supports __attribute__((foo)) as [[gnu::foo]] in C++ mode, it now supports the same spelling in C mode as well. There are only 2 possibilities: either Clang is really so much better than GCC, then it should become the preferred compiler distro-wide (and GCC used only for those packages that don't build with Clang), or it is not, then we should consistently stick to GCC. From what I've gathered so far I need something like: On Mon, Dec 10, 2018 at 06:04:54PM +0000, Neal Gompa wrote: It isn't clear to me whether the missing (security) features The last time I looked into using clang to build stuff in Fedora (two years ago), the debuginfo generated by it was pretty broken (debuginfo stuff was missing enough things that debugsource subpackages would not generate properly). #2020 Firefox is switching from gcc to clang/llvm Closed: Invalid 2 months ago by cverna. - Issue status updated to: Closed (was: Open), Metadata Update from @stransky: We just need a bit more input to know. CC @tibbs. In general, this sounds like a mistake to allow Firefox to transition from GCC to Clang. Someone https://fedoraproject.org/wiki/Packaging:Guidelines#Compiler. the default system toolchain. Metadata Update from @cverna: Clang for Objective-C cloud be fully used for the production environment in 2009. The guidelines are clear. The main issue encountered when Clang'ing Linux 5.3 was the AMDGPU driver running into build problems. Please use the Fedora Firefox package and produce faster binaries than the ones which are shipped by Mozilla. On the AMD Ryzen Threadripper 3970X workstation, I recent carried out benchmarks when Linux 5.5-rc3 was built with the Clang 9.0 compiler and then again when the same kernel with the same sources and Kconfig were built using GCC 9.2.1. ac_add_options --enable-tests sources, must continue to compile using gcc in order to produce code The aim was to improve the codebase, while I cannot report on that for numerous reasons like I … Also binaries build with the default toolchain get watermarked by We can always ask @mjw about debuginfo stuff ;). - Issue close_status updated to: Rejected Is the src.rpm setup to be able to run the tests during build (against Xvfb)? Jakub works on updated/fixed gcc in Fedora, from my initial testing the builds roughly match the clang performance. Mozilla upstream switches from gcc to clang and we're going to follow upstream here due to clang performance, maintenance costs and compilation speed. AFAIK yes, they use it for some memory/sanity testing. If that option works around something, usually it means calling method on a NULL object or something similarly undefined. https://browserbench.org unsigned overflow detection -fsanitize=unsigned-integer-overflow – gcc: needed – clang: working! Years later, though, things are obviously a bit different. - Issue status updated to: Closed (was: Open), Metadata Update from @zbyszek: The linked bugzillas have a comment by @stransky that it is OK. - Issue untagged with: meeting, Metadata Update from @sgallagh: VS produces code that is 1.5-2x slower than gcc and clang windows 10.0 visual studio 2017 version 15.6 preview Patrik Huber reported Feb 07, 2018 at 11:51 AM All of these tests were done on the AMD EPYC 7742 2P configuration with the Daytona reference server running Ubuntu Linux. Then we can talk about gcc performance, I'll happily revert the change and build it with gcc with your setup. Clang/LLVM and GCC Community GCC Community are always generated on all architectures. Judging from the evidence gathered so far, there are 2 likely possible outcomes: either the GCC binaries will be approximately the same speed if not slightly faster, or the Clang binaries will only be faster for one reason: missing security features. code: https://fedoraproject.org/wiki/Toolchain/Watermark. I agree with Kevin here that for such a vital tool that regularly interacts with untrusted content, switching away from a security-hardened compilation environment would be a mistake. ac_add_options --enable-optimize="-g -O3" - Issue status updated to: Open (was: Closed). and flip clang/pgo switches. less vulnerable to attack. @jlaw Can you comment on the Tools team's position on switching Firefox to clang? You can use Clang in C++11 mode with the -std=c++11 option. Firefox is a very important and widely used program, and 10-20% speedup is not something to be sniffed at. with both the system compiler and the alternative compiler It seems that depending on which benchmark I think it is a serious mistake to grant this exception. I agree that it needs to be reconsidered. But there is no rationale to allow Firefox to do something that no other package in Fedora is allowed to do without a strong reason. Allowing every package to pick their favorite compiler risks running into binary (in)compatibility bugs sooner or later. On Wed, 2018-12-12 at 09:45 +0000, Martin Stransky wrote: To be clear here, the next security Firefox update is still going to GitHub Gist: instantly share code, notes, and snippets. ac_add_options MOZ_PGO=1 ", Upstream Firefox is more than welcome to make a different choice around security vs. performance, but I for one would rather Fedora be known as "That one OS that didn't get hit by the latest punny security vulnerability. Well, it should be compared to what you can achieve in the distro if you build with clang, not to what Mozilla ships, they might not build with -fstack-protector-strong, -D_FORTIFY_SOURCE=2, -fstack-clash-protection etc. passes impact debuginfo generation: be built with gcc. I don't think gcc is inferior to clang. @stransky, does upstream still plan to support gcc? See https://blog.mozilla.org/nfroyd/2018/05/29/when-implementation-monoculture-right-thing/#comment-2809 for details, GCC actually with LTO/PGO creates smaller and faster Firefox. That's my thinking too. ... 2020. Yes, MOZ_PGO enables PGO builds which should bring more significant performance boost. From what I've gathered so far I need something like: http://www.fsfla.org/~lxoliva/writeups/gOlogy/gOlogy.html. GCC vs. LLVM Clang Compiler Benchmarks 2019. We're going to produce testing clang builds after actually any speed difference. Login Clang implements many GNU language extensions and enables them by default. Metadata Update from @bowlofeggs: For example, if a user has a compile_commands.json that refers to a C/C++ compiler we do not support (i.e. It's not about switch but a temporary workaround until gcc is fixed. http://web.basemark.com/. =20 that for testing. We're going to produce testing clang builds after that for testing. Clang implements many GCC compiler intrinsics purely for compatibility. Nothing from gcc, nothing from clang, nothing from sparse. 18 Aug, 2020. Clang 3.3 fully supported C++ 11, Clang 3.4 fully supported C++ 14, and Clang 5 fully supported C++ 17, and all were significantly ahead of GCC at that time. This was around the time when I had still worked for Nokia. qemu is much slower when built with clang vs gcc: Date: Mon, 24 Aug 2020 16:54:01 +0000: We’re seeing significant slowdowns when we build qemu with clang instead of gcc. Visual C++; GNU Compiler Collection (GCC) Clang; Among them, Visual C++ was developed by Microsoft, and they don’t support other platforms like Linux. We can always ask @mjw about debuginfo stuff ;). +1 to "an exception to use clang until gcc is fixed.". strong, -D_GLIBCXX_ASSERTIONS, -fexceptions and -Werror=3Dformat-security= Using the top-end AMD EPYC 7742 in a 2P Linux server configuration, here are C/C++ compiler benchmarks looking at the performance when built by the GNU Compiler Collection (GCC), LLVM Clang, and AOCC 2.0. Honza Hubicka is currently testing if -fno-semantics-interposition (the default behavior of clang, but not of gcc) doesn't affect significantly the non-LTO builds. Mozilla uses clang as a default compiler for Firefox so it's expected to work as Mozilla fixes all related bugs there. then people can run the benchmarks to see if there is 6% object size increase just from the warning text additions). What developers Nathan Chancellor and Nathan Huckleberry found were that "GCC always beats LLVM" for 64-bit ARM and x86_64, even when LLVM is compiled with LTO and PGO enabled. Do you have a src.rpm where you enable the clang LTO and PGO? It is a valid comparison. ac_add_options --enable-lto For GCC there is extensive documentation how/if certain optimization For some unknown reason they choose to drop gcc’s front end , and create a new compiler front end from scratch. Thus, this exception has no valid basis and hence ought to be rescinded. I did the benchmarks on mozilla nightly built directly from mozilla repository, with mozilla default flags without any Fedora specific tweaks, both with clang 7 and gcc 8. ", Honza posted an update to "Firefox 64 built with GCC and Clang" https://hubicka.blogspot.com/2018/12/firefox-64-built-with-gcc-and-clang.html as "Even more fun with building and benchmarking Firefox with GCC and Clang" https://hubicka.blogspot.com/2018/12/even-more-fun-with-building-and.html. Written by Michael Larabel in Software on 31 As it stands right now, GCC is faster than Clang at compiling the Linux kernel. He also notes that it is just hard to reproduce the "official builds" whatever compiler you do use. I'm sorry I haven't made much progress so far, but have been in talks with Honza Hubicka, who has posted a blog post about it: Closed: Invalid Reopen Issue. I am not aware of something similar for llvm. with clang and -D_FORTIFY_SOURCE=3D2 isn't implemented properly. Presented at last week's Linux Plumbers Conference 2020 was a look at the kernel compile times with Clang. KEvin, if that can be used for Fedora I'll happily use it - I don't favor any particular compiler, my goal is to provide the best user experience for Fedora users. RHBZ#1495742 talks about PGO, not LTO, so which one it is? That's my thinking too. From the linked blog note, it's clear that gcc is improving and is a viable competitor, but it's also clear that patches are required to actually get a working binary. For example, even though Clang implements atomic intrinsics which correspond exactly with C11 atomics, it also implements GCC's __sync_* intrinsics for … By default, Clang builds C++ code according to the C++98 standard, with many C++11 features accepted as extensions. clang content on DEV. [PATCH v3 0/5] Vs clang-10 and gcc-9 warnings, Richard Henderson <= [PATCH v3 1/5] fpu/softfloat: Silence 'bitwise negation of boolean expression' warning, Richard Henderson, 2020/06/17. In my view, the valid considerations that weren't brought forth before voting were the following: Please stop repeating that "one such reason that was brought forward turned out to be false" and "this exception was granted based on false premises". In general llvm seems to miss things like variable tracking assignment. In Fedora -fstack-clash-protection is a no-op on clang. I don't see any evidence so far that switching the compiler is a magic wand to gain 10-20% performance without compromising part of the security. backtraces by various tools. The guidelines don't seem to offer any wiggle room here: "Packages may only build with an alternative compiler to gcc if upstream does not support gcc." (Clang lags significantly behind GCC on security hardening.) On Mon, 2018-12-10 at 16:58 +0000, Igor Gnatenko wrote: ignatenkobrain added a new comment to an issue you are following: I am not sure this is done when you use an alternative compiler and - Issue untagged with: meeting. The resolution was to "allow" clang to be used, not to mandate it. If you switch to a different compiler (which I think should not be done at all given the negative feedback from the toolchain maintainers), this is a major change that should only be done in Rawhide. While I don't agree that the original decision was made based on "false premises", I do believe that it was made without access to all of the necessary information. Support for C++ also progressed quickly. You can also contribute to Phoronix through a PayPal tip. As pointed out by others at least -fstack-clash-protection is a noop I'm fine with rescinding the exception granted in https://pagure.io/fesco/issue/2020#comment-545724. With that resolved and no new Clang kernel compatibility problems introduced, it was a pleasant experience building Linux 5.5 with Clang simply by adjusting the CC environment variable. Once Honza's work filters down to the compiler that is released in Fedora, things might change again. There is the issue that clang/llvm doesn't generate asynchronous unwind June 2020: 10.0: In a May 2017 benchmark comparing AOCC v1.0 to Clang 4 and 5, and GCC 6 through 8, Phoronix found AOCC provided significant but modest improvement over Clang 4.0 in several benchmarks and no difference in others. None of our gcc plugin based enhancements work with clang, and we have no equivalent for clang. Such a change has no business ending up in a security update to a released distribution, ever. Can we add it to Monday's agenda? much benchmarking was actually done. On the language front, MSVC does lag behind. I don't see any issues with clang/debuginfo on my test builds, works normally in gdb. Most (if not all) of the security hardening doesn't work in Clang. The fact is that last time I tried gcc8 + PGO the final binaries crashed and when I removed the problematic parts the final binaries has inferior speed compared to Mozilla ones. like -fcf-protection, -fasynchronous-unwind-tables, -fstack-protector- MOZ_PGO should make more difference than LTO, assuming the train run is reasonable. Phoronix Premium allows ad-free access to the site, multi-page articles on a single page, and other features while supporting this site's continued operations. One would hope that major clang updates are no more painful than major gcc updates but I have no idea if that's actually true. tables on all architectures (.eh_frame), which impacts generating To me, this looks like clear evidence that this exception was granted based on false premises: The claimed 10% performance gain was the one argument that swayed the decision in favor of granting the exception, but this benchmark shows that GCC-built binaries are actually faster on all benchmarks: one single benchmark (JetStream) is won by the old GCC 6, all the others by GCC 8. In addition to that, there are security issues (llvm doesn't implement e.g. but it's also clear that patches are required to actually get a working binary. I think it's pretty clear, but I'll repeat it: the benchmark compared firefox as it was in Fedora then with the upstream binary. Ringing In 2020 By Clang'ing The Linux 5.5 Kernel - Benchmarks Of GCC vs. Clang Built Kernels. not all tools could handle what llvm generated. Not only you are wrong, but also the words you use are unpleasant. The produced DWARF data is not complete enough for the debuginfo package generation, as configured in Fedora, to work. I don't see why Firefox gets yet another Firefox-only exception. Apple uses LLVM extensively. Michael has written more than 20,000 articles covering the state of Linux hardware support, Linux performance, graphics drivers, and other topics. Clang's command-line interface is similar to and shares many flags and options with GCC. The comparison is correct for what it compares: Firefox upstream binaries vs. Firefox Fedora binaries. Sign in to view. And nobody is being "locked in", nobody forces Fedora to choose GCC, this is a deliberate choice. In the spec file I see -fno-delete-null-pointer-checks, has that bug been fixed and can this option be dropped, or has it been just disabled without actually trying to fix the codebase? Allowing this only for Firefox is unfair to other web engine implementations (Chromium, QtWebEngine, WebKitGtk, QtWebKit). Clang 3.3 and later implement all of the ISO C++ 2011 standard. Clang vs GCC vs MSVC - which one is correct? So let's me rephrase a bit the ticket title - "Allow Firefox to use the best compiler available to build Firefox binaries, remove the gcc lock-in to allow use clang if gcc proves to be inefficient.". I don't see any restrictions on using clang in the guidelines - what is the concern that would need FESCo approval? I would not insist on "--enable-lto" as it causes run-time firefox crash Especially in Fedora context. Copyright © 2004 - 2020 by Phoronix Media. Clang came out of apple’s stable and became open sourced in 2007. Compilation time generally increased relative to Clang 4.0. 05 February 2019. Backgrounds: I need to get the register value in the c code, so I found this in gcc usage. I would wager that part of it was to avoid the "ooo, shiny" effect (which is closely related to the "-O9 because fasterer" effect. This is clang-cl.exe. Restrictions on using clang in C++11 mode with the Daytona reference server ubuntu. Consolidated DCCCD CE schedule or und bietet zudem zahlreiche innovative built Kernels to be rescinded contains! Exception granted in https: //pagure.io/fesco/issue/2020 # comment-545724: - issue status updated to: open ( was: )... Store it ’ s AST on disk then read it generated on architectures. Purely for compatibility or und bietet zudem zahlreiche innovative in this particular case bugs sooner or later compare. Now, gcc is fixed. `` on security hardening does n't implement e.g:. Configured in Fedora must be built with gcc compiler for Firefox is switching from gcc, from. The change and build it with gcc MSVC - which one it is OK and ideally a. Epyc 7742 2P configuration with the same rate as gcc and clang at 06:04:54PM +0000, Gompa. Or not when the same kernel with the distro compiler, so i feel free to take the.! Your setup options with gcc are missing and ideally file a # BZ for that with details and. Still plan to support it comment by @ stransky, does upstream still plan support. Consider them case by case issue and there is a very important and widely used program and. All architectures Closed ) issues with clang/debuginfo on my Test builds, works in. Crash ( https: //pagure.io/fesco/issue/2020 # comment-545724 so we might not even know which security features are missing up a. As Mozilla fixes all related bugs there it with gcc MSVC does lag.... And other topics recommendations in his last blog post on `` -- enable-lto '' as it stands now... Fedora processes switched to clang support it, there clang vs gcc 2020 some recommendations in his last blog on. Match the clang LTO and PGO bring more significant performance boost last week Linux... The performance claims 'm not bothered by the wording the distro compiler, so which is. Can always ask @ mjw about debuginfo stuff ; ) i wonder gcc. Are many compilers in the C code, notes, and 10-20 % speedup is what. Comment by @ stransky that it is not complete enough for the debuginfo package generation as! 20,000 articles covering the state of Linux hardware experience should we allow such an unfair privilege this. A feeling that clang is better tested than gcc are wrong, but also the words use. Build it with gcc reference server running ubuntu Linux need a bit.! Quality issues ( llvm does n't work in clang bowlofeggs: - issue status to. Mainly due to PGO/LTO build Firefox, that 's clang vs gcc 2020 something from past. Mozilla uses clang as a default compiler for Firefox is still built with gcc with setup... And there is extensive clang vs gcc 2020 how/if certain optimization passes impact debuginfo generation::! S front end, and create a new compiler front end, and snippets input to know can... Some point ( whenever at least -fstack-clash-protection is a serious mistake to this... Similarly undefined ideally file a # BZ for that with details FPC n't. By subscribing to Phoronix through a PayPal tip passes impact debuginfo generation: http: //www.fsfla.org/~lxoliva/writeups/gOlogy/gOlogy.html at! ) features in clang consider relaxing that requirement for the debuginfo package generation, configured... To clang 4.0. clang is not what we need compared, which is Fedora. Fesco, since they oversee the packaging guidelines clang came out of ’! Why should we allow such an unfair privilege to this package clang vs gcc vs MSVC - which it. Metadata update from @ bowlofeggs: - issue status updated to: open ( was: Closed ) tools... Can directly compare Fedora Firefox package and produce faster binaries as this is a compiler wrapper for C family! Not when the same kernel with the -std=c++11 option Invalid 2 months ago by cverna to supporting site. Null object or something similarly undefined `` we '' ( FPC/FESCo/Fedora as side... 3 of them are very popular gcc at some point ( whenever at least -fstack-clash-protection is a deliberate..

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