Re: New assembler warnings with binutils 2.29
On 08/14/2017 07:45 AM, Ramana Radhakrishnan wrote: > On Mon, Aug 14, 2017 at 11:34:45AM +0100, Catalin Marinas wrote: >>> >>> 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! > > I've submitted the patch upstream and would appreciate any testing of kernel > builds to double check that this fixes the issue at hand. > > https://sourceware.org/ml/binutils/2017-08/msg00160.html I verified on a local build that this makes the warnings go away. Thanks, Laura > > > Ramana
Re: New assembler warnings with binutils 2.29
On Mon, Aug 14, 2017 at 11:34:45AM +0100, Catalin Marinas wrote: > > > > 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! I've submitted the patch upstream and would appreciate any testing of kernel builds to double check that this fixes the issue at hand. https://sourceware.org/ml/binutils/2017-08/msg00160.html Ramana > > -- > Catalin
Re: New assembler warnings with binutils 2.29
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 > > > 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 .reqx30 // 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
Re: New assembler warnings with binutils 2.29
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 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 .reqx30 // 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 :) > > > > 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. 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. I'll do a test run and post it on the lists and point you guys to it (probably now after lunch as I have a couple of meetings to run to) so that you could also test it and let us know if there are any issues. regards Ramana
Re: New assembler warnings with binutils 2.29
On Fri, Aug 11, 2017 at 10:26:06AM +0100, Ard Biesheuvel wrote: > On 11 August 2017 at 10:22, Catalin Marinas 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 .reqx30 // 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... > > > > 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: a) binutils reverts the change b) we stop using lr etc. in Linux for good (since you can't tell which gas supports them) c) we replace .req with #define in the kernel My preference is (a) but we can go for (c) as being more under our control. -- Catalin
Re: New assembler warnings with binutils 2.29
On 11 August 2017 at 10:34, Arnd Bergmann wrote: > On Fri, Aug 11, 2017 at 11:26 AM, Ard Biesheuvel > wrote: >> On 11 August 2017 at 10:22, Catalin Marinas 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 .reqx30 // 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... >>> >>> 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 x30 with lr achieves the opposite of the Of course, I meant replacing lr with x30 in our code. >> 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? > > adding the author of the change to cc > > https://sourceware.org/git/?p=binutils-gdb.git;a=commitdiff;h=62e20ed45e3da5f3ba695e4ee109317668180fe6 > > There probably was some reasoning behind the change and an > intended method for using it. > > Arnd
Re: New assembler warnings with binutils 2.29
On Fri, Aug 11, 2017 at 11:26 AM, Ard Biesheuvel wrote: > On 11 August 2017 at 10:22, Catalin Marinas 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 .reqx30 // 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... >> >> 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 x30 with lr 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? adding the author of the change to cc https://sourceware.org/git/?p=binutils-gdb.git;a=commitdiff;h=62e20ed45e3da5f3ba695e4ee109317668180fe6 There probably was some reasoning behind the change and an intended method for using it. Arnd
Re: New assembler warnings with binutils 2.29
On 11 August 2017 at 10:22, Catalin Marinas 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 .reqx30 // 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... > > 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 x30 with lr 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?
Re: New assembler warnings with binutils 2.29
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 .reqx30 // 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... 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. -- Catalin
New assembler warnings with binutils 2.29
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 .reqx30 // link register https://kojipkgs.fedoraproject.org//packages/kernel/4.13.0/0.rc2.git2.1.fc27/data/logs/aarch64/build.log has an example log. As far as I can tell this doesn't affect anything at runtime. Any ideas? Thanks, Laura
