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From: "segher at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug target/102485] -Wa,-many no longer has any effect Date: Wed, 23 Feb 2022 17:38:25 +0000 [thread overview] Message-ID: <bug-102485-4-VckIMwIK19@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-102485-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102485 Segher Boessenkool <segher at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Status|UNCONFIRMED |RESOLVED Resolution|--- |INVALID --- Comment #7 from Segher Boessenkool <segher at gcc dot gnu.org> --- > GCC already passes -m<cpu> to the assembler though. That mostly is historic. > The justification for emitting the .machine directive is given as fixing a > build breakage due to a build system that passes an incorrect -m<cpu> to the > assembler. Not really, no. That is just one tiny part of the problem. It is impossible to know what instruction sets we need ahead of time, and -many cannot work (and *does not* work: there are quite a few mnemonics that encode to different insns on different architecture versions (or for different CPUs), and we cannot know which is wanted, or which is preferred, ahead of time. > *That* is the broken code (if any) that should have been fixed. But instead > that is hacked around in a way that breaks working code that passes down > -Wa,-many option as specified. There is no working code that uses -many (accept by accident, if no problem has hit you yet). > The kernel builds with a base compatibility (say -mcpu=power4) and then has > certain code paths that are dynamically taken if running on newer CPUs which > use newer instructions with inline asm. > > This is an important usage and it's pervasive, it seems unreasonable to > break it. Adding .machine directives throughout inline asm for every > instruction not in the base compatibility class is pretty horrible. It is the only correct thing to do.
next prev parent reply other threads:[~2022-02-23 17:38 UTC|newest] Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-09-25 21:27 [Bug target/102485] New: " pc at us dot ibm.com 2021-10-04 17:26 ` [Bug target/102485] " bergner at gcc dot gnu.org 2021-10-04 18:17 ` pc at us dot ibm.com 2021-10-05 22:11 ` segher at gcc dot gnu.org 2021-10-05 22:58 ` bergner at gcc dot gnu.org 2021-10-05 23:41 ` segher at gcc dot gnu.org 2022-02-23 17:11 ` npiggin at gmail dot com 2022-02-23 17:38 ` segher at gcc dot gnu.org [this message] 2022-02-24 1:11 ` npiggin at gmail dot com 2022-02-24 1:25 ` npiggin at gmail dot com 2022-02-24 11:07 ` amodra at gmail dot com
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