On Tue, Jan 20, 2015 at 7:02 PM, Alan Modra <amo...@gmail.com> wrote: > On Tue, Jan 20, 2015 at 09:26:12AM -0500, David Edelsohn wrote: >> On Tue, Jan 20, 2015 at 12:41 AM, Alan Modra <amo...@gmail.com> wrote: >> > On Mon, Jan 19, 2015 at 10:43:29PM -0500, David Edelsohn wrote: >> >> On Fri, Jan 17, 2014 at 10:58 PM, Alan Modra <amo...@gmail.com> wrote: >> >> > This patch cures PR59828 by translating all the -mcpu options at once, >> >> > in order, to their equivalent assembler -m options by using a new spec >> >> > function. In the process this removes some duplication. >> >> >> >> ASM_CPU_SPEC is too fragile a mechanism. I would much prefer to >> >> expand on the ".machine" directive that I added to >> >> rs6000_file_start(). The initial implementation explicitly avoids >> >> .machine when -mcpu= or --with-cpu= is present as a conservative >> >> start. >> >> >> >> It seems much better to select a .machine directive based on the >> >> actual target ISA flag bits enabled than translating CPU command line >> >> options to ASM options. Patches to replace ASM_CPU_SPEC with .machine >> >> and expand functionality for AIX are welcome. >> > >> > This might make sense when looking only at gcc, but when considering >> > the whole toolchain I think you'll run into difficulty. gas and other >> > powerpc assemblers have always been invoked with -m options to select >> > the cpu, so if you do away with ASM_CPU_SPEC and rely on .machine then >> > you will be exercising the assembler in a new way. I am sure that >> > this will not work for all powerpc assemblers currently in use. >> >> It is stressing .machine more than that feature has been in the past, >> but it is functionality that is suppose to work. .machine already has >> been stressed more with IFUNC pushing and popping ISAs. >> >> Are you concerned about the fundamental functionality of the pseudo-op >> or a particular GAS release missing support for a particular ISA? AIX >> supports .machine, but I think that it expects slightly different >> processor names. I am not certain about LLVM-AS, but it normally is >> not fed external assembly language files. > > I'm concerned about initialisation that might happen based on a -m > option that doesn't happen with .machine. A quick look over the > gas source showed we currently have at least one case like this: > ppc_dwarf2_line_min_insn_length is only set from command line -m > options. This means that if you want debug with VLE insns, you cannot > currently invoke gas without -mvle. ".machine vle" by itself won't > work. I think there may be other similar problems with setting the > bfd arch/mach pair.
We can leave VLE unaffected and ensure that rs6000_file_start does not emit a .machine directive for VLE or emits both .machine vle and the driver retains the -mvle assembler command line option. This does not need to be one extreme or the other. We can remove as much -mcpu=XXX as we can, which should avoid most of the conflicting and duplicative directives. In the mean time, GAS can be fixed. I want to avoid duplicating the -mcpu parsing logic or the Rube Goldberg mechanism to re-generate the -mXXX assembler directive. Thanks, David
