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What is different of the function call and return manner between  ARM Linux kernel and ARM applications？

Heron Zhang
Note: This was originally posted on 29th August 2012 at http://forums.arm.com

Hi,

When I disassamble the ARM Linux kernel for ARMv7(tegra 2),I found that a lot of function return using ldm command,just like   ldm sp,  {fp, sp, pc},but in the applications ( SPECCPU2006 for arm),the function return mostly using bx or b.Why that happened? Is the kernel Makefile used some gcc arguments that can lead the compiler to optimize the kernel?
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  • Arm Employee Badge
    Note: This was originally posted on 29th August 2012 at http://forums.arm.com

    One note....
    The rules changed in v7. Per-v7 data processing instructions couldn't cause a state (ARM/Thumb) change. So "mov pc, lr" couldn't return you a function in a different instruction set. From v7 onwards, any data processing instruction with the pc as the destination CAN change state. So  it now doesn't matter.
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  • Arm Employee Badge
    Note: This was originally posted on 29th August 2012 at http://forums.arm.com

    One note....
    The rules changed in v7. Per-v7 data processing instructions couldn't cause a state (ARM/Thumb) change. So "mov pc, lr" couldn't return you a function in a different instruction set. From v7 onwards, any data processing instruction with the pc as the destination CAN change state. So  it now doesn't matter.
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