| Message ID | 20211115011313.GA43897@embeddedor (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | kbuild: Fix -Wimplicit-fallthrough=5 error for GCC 5.x and 6.x | expand |
On Sun, Nov 14, 2021 at 5:08 PM Gustavo A. R. Silva <gustavoars@kernel.org> wrote: > > -Wimplicit-fallthrough=5 was under cc-option because it was only > available in GCC 7.x and newer so the build is now broken for GCC 5.x > and 6.x: Annoying. And I obviously never saw it because I don't carry ancient compiler versions. That said: > - default "-Wimplicit-fallthrough=5" if CC_IS_GCC > + default "-Wimplicit-fallthrough=5" if $(cc-option,-Wimplicit-fallthrough=5) I think it would be better to keep the CC_IS_GCC part of the test, for the simple reason that the clang "make config" is already very slow. I'm not sure why, but it's annoyingly noticeable, and I've complained about clang performance before in this area (and the likely cause is the default build for clang being this horribly inefficient shared library setup, so it spends ages just doing dynamic linking) Whenever I do "make oldconfig" with a clang build, and my machine is under any reasonable load (typically because I'm also doing another build in another terminal at the same time), it takes several seconds. Doing the same thing with gcc is noticeably much faster. In fact, it doesn't even need to be a very loaded machine, this is basically an empty "re-do config" with gcc vs clang (basically same config, except obviously for compiler-induced config differences): gcc$ time make oldconfig real 0m0.929s clang$ time make oldconfig real 0m1.917s Two seconds may not seem like a lot, but when the machine is under my usual build load, that almost 2s easily becomes a "do I need to go for coffee" delay, since I'm just waiting for the config to finish before I start the build (since I may end up having to answer questions). And yeah, it's sad how much faster gcc is. There was a time when the clang people were proud of their compile-time performance. Pepperidge farm remembers. Anyway, I'd prefer to not ask for the clang build to do even more work, since we know it will fail that '=5' case. Linus
diff --git a/init/Kconfig b/init/Kconfig index 036b750e8d8a..85882c317235 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -887,7 +887,7 @@ config CC_HAS_INT128 config CC_IMPLICIT_FALLTHROUGH string - default "-Wimplicit-fallthrough=5" if CC_IS_GCC + default "-Wimplicit-fallthrough=5" if $(cc-option,-Wimplicit-fallthrough=5) default "-Wimplicit-fallthrough" if CC_IS_CLANG && $(cc-option,-Wunreachable-code-fallthrough) #