Russell King - ARM Linux <linux@xxxxxxxxxxxxxxxx> writes: > 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. Then what do you mean? The compiler either emits the instructions or it doesn't. If it doesn't, what the assembler accepts is irrelevant. -- Måns Rullgård mans@xxxxxxxxx -- 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
