On Fri, Jul 08, 2022 at 11:44:54AM +0200, Helge Deller wrote: > In the kernel image vmlinux.lds.S linker scripts the .altinstructions > and __bug_table sections are 4- or 8-byte aligned because they hold 32- > and/or 64-bit values. > > Most architectures use altinstructions and BUG() or WARN() in modules as > well, but in the module linker script (module.lds.S) those sections are > currently missing. As consequence the linker will store their content > byte-aligned by default, which then can lead to unnecessary unaligned > memory accesses by the CPU when those tables are processed at runtime. > > Usually unaligned memory accesses are unnoticed, because either the > hardware (as on x86 CPUs) or in-kernel exception handlers (e.g. on > parisc or sparc) emulate and fix them up at runtime. Nevertheless, such > unaligned accesses introduce a performance penalty and can even crash > the kernel if there is a bug in the unalignment exception handlers > (which happened once to me on the parisc architecture and which is why I > noticed that issue at all). > > This patch fixes a non-critical issue and might be backported at any time. > It's trivial and shouldn't introduce any regression because it simply > tells the linker to use a different (8-byte alignment) for those > sections by default. > > Signed-off-by: Helge Deller <deller@xxxxxx> > Link: https://lore.kernel.org/all/Yr8%2Fgr8e8I7tVX4d@p100/ Thanks! Queued onto modules-next. Luis
