| Message ID | 1297093986-24331-1-git-send-email-enrico.scholz@sigma-chemnitz.de |
|---|---|
| State | Accepted |
| Delegated to: | Khem Raj |
| Headers | show |
diff --git a/conf/machine/include/tune-cortexm3.inc b/conf/machine/include/tune-cortexm3.inc index 6da9aee..a66a33c 100644 --- a/conf/machine/include/tune-cortexm3.inc +++ b/conf/machine/include/tune-cortexm3.inc @@ -1,4 +1,4 @@ # valid options for -march: `armv7', `armv7-m' -TARGET_CC_ARCH = "-march=armv7-m -mtune=cortex-m3 -mfpu=vfp -mfloat-abi=softfp" +TARGET_CC_ARCH = "-mthumb -mcpu=cortex-m3 -mfpu=vfp -mfloat-abi=softfp" FEED_ARCH = "armv7" BASE_PACKAGE_ARCH = "armv7"
On 2/7/11 1:33 PM, Khem Raj wrote: > On Mon, Feb 7, 2011 at 7:53 AM, Enrico Scholz > <enrico.scholz@sigma-chemnitz.de> wrote: >> Explicit '-mthumb' is required because Cortex-M3 does not support ARM >> instructions and actual flags cause gcc to fail with 'error: target CPU >> does not support ARM mode'. >> >> The '-mcpu=cortex-m3' is shorter than '-march=armv7-m -mtune=cortex-m3' >> and enables workarounds like '-mfix-cortex-m3-ldrd'. > > Does -mcpu=cortex-m3 also cause gcc to tune for cortex-m3 ? -mcpu=cortex-m3 is equivalent to -march=cortex-m3 -mtune=cortex-m3 So in this instance, it will have a side effect of potentially changing the available set of instructions.. The existing command says the only available instructions are those defined as "armv7-m", but I want to tune the instruction scheduler for execution on "cortex-m3". (I'm not an ARM expert, so I'm not sure what is reasonable in this case.. but the arguments do have slightly different meanings.) --Mark >> >> Signed-off-by: Enrico Scholz <enrico.scholz@sigma-chemnitz.de> >> --- >> conf/machine/include/tune-cortexm3.inc | 2 +- >> 1 files changed, 1 insertions(+), 1 deletions(-) >> >> diff --git a/conf/machine/include/tune-cortexm3.inc b/conf/machine/include/tune-cortexm3.inc >> index 6da9aee..a66a33c 100644 >> --- a/conf/machine/include/tune-cortexm3.inc >> +++ b/conf/machine/include/tune-cortexm3.inc >> @@ -1,4 +1,4 @@ >> # valid options for -march: `armv7', `armv7-m' >> -TARGET_CC_ARCH = "-march=armv7-m -mtune=cortex-m3 -mfpu=vfp -mfloat-abi=softfp" >> +TARGET_CC_ARCH = "-mthumb -mcpu=cortex-m3 -mfpu=vfp -mfloat-abi=softfp" >> FEED_ARCH = "armv7" >> BASE_PACKAGE_ARCH = "armv7" >> -- >> 1.7.4 >> >> >> _______________________________________________ >> Openembedded-devel mailing list >> Openembedded-devel@lists.openembedded.org >> http://lists.linuxtogo.org/cgi-bin/mailman/listinfo/openembedded-devel >> > > _______________________________________________ > Openembedded-devel mailing list > Openembedded-devel@lists.openembedded.org > http://lists.linuxtogo.org/cgi-bin/mailman/listinfo/openembedded-devel
On Mon, Feb 7, 2011 at 11:39 AM, Mark Hatle <mark.hatle@windriver.com> wrote: > On 2/7/11 1:33 PM, Khem Raj wrote: >> On Mon, Feb 7, 2011 at 7:53 AM, Enrico Scholz >> <enrico.scholz@sigma-chemnitz.de> wrote: >>> Explicit '-mthumb' is required because Cortex-M3 does not support ARM >>> instructions and actual flags cause gcc to fail with 'error: target CPU >>> does not support ARM mode'. >>> >>> The '-mcpu=cortex-m3' is shorter than '-march=armv7-m -mtune=cortex-m3' >>> and enables workarounds like '-mfix-cortex-m3-ldrd'. >> >> Does -mcpu=cortex-m3 also cause gcc to tune for cortex-m3 ? > > -mcpu=cortex-m3 is equivalent to -march=cortex-m3 -mtune=cortex-m3 is -march=cortex-m3 valid even ? my question was if we select armv7-m using -march then gcc knows stuff like oh this arch has a hardware div instruction but now if we use -mcpu will it still do it.
On 2/7/11 2:19 PM, Khem Raj wrote: > On Mon, Feb 7, 2011 at 11:39 AM, Mark Hatle <mark.hatle@windriver.com> wrote: >> On 2/7/11 1:33 PM, Khem Raj wrote: >>> On Mon, Feb 7, 2011 at 7:53 AM, Enrico Scholz >>> <enrico.scholz@sigma-chemnitz.de> wrote: >>>> Explicit '-mthumb' is required because Cortex-M3 does not support ARM >>>> instructions and actual flags cause gcc to fail with 'error: target CPU >>>> does not support ARM mode'. >>>> >>>> The '-mcpu=cortex-m3' is shorter than '-march=armv7-m -mtune=cortex-m3' >>>> and enables workarounds like '-mfix-cortex-m3-ldrd'. >>> >>> Does -mcpu=cortex-m3 also cause gcc to tune for cortex-m3 ? >> >> -mcpu=cortex-m3 is equivalent to -march=cortex-m3 -mtune=cortex-m3 > > is -march=cortex-m3 valid even ? my question was if we select armv7-m > using -march > then gcc knows stuff like oh this arch has a hardware div instruction > but now if we > use -mcpu will it still do it. You would have to look in the source and see if -mcpu=cortex-m3 is an "alias" for anything or simply uses the default logic of cpu == march && mtune.. (FYI, last time I looked at how this worked was a year or so ago.. so if the way GCC processes options has changed, then I'm wrong.. but it's worth looking at.. I was scolded many times by GCC developers that -mcpu= is not the same as specifically setting the arch and tune.) Usually you use march & mtune when you are trying to make a set of binaries that is capable of running on multiple cores in the same family. I see it used the most of IA and Power systems myself. --Mark
Khem Raj <raj.khem@gmail.com> writes: >> The '-mcpu=cortex-m3' is shorter than '-march=armv7-m -mtune=cortex-m3' >> and enables workarounds like '-mfix-cortex-m3-ldrd'. > > Does -mcpu=cortex-m3 also cause gcc to tune for cortex-m3 ? Yes; logic in gcc/config/arm/arm.c is: | if (i == ARM_OPT_SET_CPU || i == ARM_OPT_SET_TUNE) | arm_tune = (enum processor_type) (sel - ptr->processors); | | if (i == ARM_OPT_SET_ARCH) | target_arch_cpu = sel->core; | | if (i == ARM_OPT_SET_CPU) | selected_cpu = (enum processor_type) (sel - ptr->processors); '-mcpu' causes the highest optimization level (both for the used instruction set (--> '-march') and the "soft" optimizations (--> '-mcpu')). Enrico
Khem Raj <raj.khem@gmail.com> writes: > Can you check what does gcc emits in an assembly file when using > -mcpu=cortex-m3 in your case. If it emits sdiv instruction or not > > int foo (long a, long b) > { > return a/b; > } $ arm-linux-uclibceabi-gcc -mthumb -mcpu=cortex-m3 -mfpu=vfp -mfloat-abi=softfp -O1 -c x.c $ arm-linux-uclibceabi-objdump -d x.o 00000000 <foo>: 0: fb90 f0f1 sdiv r0, r0, r1 4: 4770 bx lr 6: bf00 nop Enrico
Explicit '-mthumb' is required because Cortex-M3 does not support ARM instructions and actual flags cause gcc to fail with 'error: target CPU does not support ARM mode'. The '-mcpu=cortex-m3' is shorter than '-march=armv7-m -mtune=cortex-m3' and enables workarounds like '-mfix-cortex-m3-ldrd'. Signed-off-by: Enrico Scholz <enrico.scholz@sigma-chemnitz.de> --- conf/machine/include/tune-cortexm3.inc | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-)