Messages in this thread | | | Date | Mon, 14 Aug 2017 11:34:45 +0100 | From | Catalin Marinas <> | Subject | Re: New assembler warnings with binutils 2.29 |
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On Mon, Aug 14, 2017 at 10:55:48AM +0100, Ramana Radhakrishnan wrote: > On Mon, Aug 14, 2017 at 09:59:02AM +0100, Catalin Marinas wrote: > > On Fri, Aug 11, 2017 at 10:26:06AM +0100, Ard Biesheuvel wrote: > > > On 11 August 2017 at 10:22, Catalin Marinas <catalin.marinas@arm.com> wrote: > > > > On Thu, Aug 10, 2017 at 01:13:22PM -0700, Laura Abbott wrote: > > > >> Fedora rawhide recently upgraded to binutils 2.29 and this seems > > > >> to produce new warnings: > > > >> > > > >> ./arch/arm64/include/asm/assembler.h: Assembler messages: > > > >> ./arch/arm64/include/asm/assembler.h:125: Warning: ignoring attempt to redefine built-in register 'lr' > > > >> > > > >> This is > > > >> > > > >> /* > > > >> * Register aliases. > > > >> */ > > > >> lr .req x30 // link register > > > > > > > > Strange, does gas now think 'lr' is a general purpose register (aliased > > > > to x30)? It never was and IIRC the toolchain people many years ago > > > > refused to add it, hence the alias above in the kernel. I wonder if they > > > > added 'fp' as well... > > I don't remember the reasons why it was refused in the past. Asking around I > can't seem to find anyone who remembers why either and it would be much > quicker to fix the problem in binutils than any of this archeology :)
I don't have the old emails around either ;).
> > > > We could remove the alias and replace all 'lr' instances with 'x30' > > > > throughout the kernel (no too many) or we add some #ifdef around the > > > > above based on the binutils version. > > > > This is annoying. Replacing lr with x30 achieves the opposite of the > > > intent of the binutils change. And using #ifdefs is inaccurate, > > > because you can't really test the binutils version only the GCC > > > version, and those are not tightly coupled. > > > > Can you .unreq it? > > > > Not really, with an older binutils I get: > > > > arch/arm64/include/asm/assembler.h:125: Error: unknown register alias 'lr' > > > > I personally consider this a binutils bug. After 6+ years (probably not > > all public) of building the kernel just fine, all of a sudden certain > > strings became reserved in gas. Three options: > > IIRC the ABI states that LR is an alias for X30, FP is an alias for X29, > IP0 an alias for X16 and IP1 an alias for X17.
It's unfortunate that binutils never define them, so we ended up with .req in the kernel.
> The warning is unfortunate - looking at the implementation of the > .req directive in gas it's something controlled in the aarch64 backend > and thus we could change gas to make LR (and friends) an internal alias thus > removing the warning. > > Any attempts to realias these to the correct meaning as per the AAPCS > continues to work from my limited testing of a prototype patch so far.
This would be great. Thanks Ramana!
-- Catalin
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