mirror of
https://github.com/hardkernel/linux.git
synced 2026-06-03 01:36:52 +09:00
43c249ea0b
The workaround for 'asm goto' miscompilation introduces a compiler barrier quirk that inhibits many useful compiler optimizations. For example, __try_cmpxchg_user compiles to: 11375: 41 8b 4d 00 mov 0x0(%r13),%ecx 11379: 41 8b 02 mov (%r10),%eax 1137c: f0 0f b1 0a lock cmpxchg %ecx,(%rdx) 11380: 0f 94 c2 sete %dl 11383: 84 d2 test %dl,%dl 11385: 75 c4 jne 1134b <...> 11387: 41 89 02 mov %eax,(%r10) where the barrier inhibits flags propagation from asm when compiled with gcc-12. When the mentioned quirk is removed, the following code is generated: 11553: 41 8b 4d 00 mov 0x0(%r13),%ecx 11557: 41 8b 02 mov (%r10),%eax 1155a: f0 0f b1 0a lock cmpxchg %ecx,(%rdx) 1155e: 74 c9 je 11529 <...> 11560: 41 89 02 mov %eax,(%r10) The refered compiler bug: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58670 was fixed for gcc-4.8.2. Current minimum required version of GCC is version 5.1 which has the above 'asm goto' miscompilation fixed, so remove the workaround. Link: https://lkml.kernel.org/r/20220624141412.72274-1-ubizjak@gmail.com Signed-off-by: Uros Bizjak <ubizjak@gmail.com> Cc: Ingo Molnar <mingo@kernel.org> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.