On Tue, Nov 24, 2015 at 12:29:06PM +0000, Måns Rullgård wrote: > Russell King - ARM Linux <linux@xxxxxxxxxxxxxxxx> writes: > > > On Tue, Nov 24, 2015 at 12:10:02PM +0000, Måns Rullgård wrote: > >> Russell King - ARM Linux <linux@xxxxxxxxxxxxxxxx> writes: > >> > >> > On Tue, Nov 24, 2015 at 11:38:53AM +0100, Arnd Bergmann wrote: > >> >> I suggested using -mcpu=cortex-a15 because there are old gcc versions > >> >> that don't know about -march=armv7ve or -march=armv7-a+idiv yet, but > >> >> that do understand -mcpu=cortex-a15. > >> > > >> > That's not all. The bigger problem is that there are toolchains out > >> > there which accept these options, but do _not_ support IDIV in either > >> > ARM or Thumb mode. I'm afraid that makes it impossible to add this > >> > feature to the mainline kernel in this form: we need to run a test > >> > build to check that -march=armv7ve or what-not really does work > >> > through both GCC and GAS. > >> > >> If the compiler accepts the option but doesn't actually emit any div > >> instructions, is there any real harm? > > > > That's not what I've found. I've found that asking the assembler > > to accept idiv instructions appears to be ignored, which is something > > completely different. > > > > Further to this, what it comes down to is the stupid idea that the > > compiler should embed .arch / .cpu in the assembly output, which has > > the effect of overriding the command line arguments given to it via > > -Wa. So, giving -Wa,-mcpu=cortex-a15 is a total no-op, because the > > first thing in the assembly output is: > > > > .arch armv7-a > > > > which kills off any attempt to set the assembly level ISA from the > > command line. > > Oh, you mean the compiler knows about the instructions but the assembler > doesn't or isn't passed the right options. It's infuriating when that > happens. No, that isn't what I meant. -- FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up according to speedtest.net. -- To unsubscribe from this list: send the line "unsubscribe linux-arm-msm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
