• Locked Locked
  • Replies 4 replies
  • Subscribers 119 subscribers
  • Views 3385 views
  • Users 0 members are here
2025 survey

We are running a survey to help us improve the experience for all of our members. If you see the survey appear, please take the time to tell us about your experience if you can.

Options
Related
How was your experience today?
This discussion has been locked.
You can no longer post new replies to this discussion. If you have a question you can start a new discussion

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?
Parents
  • Note: This was originally posted on 29th August 2012 at http://forums.arm.com

    Thank you very much.

    Besides that two ways you said,an uncommon way is :Mov pc,XX.  The compiler is not intelligent,so there must be reason using different ways to return.I guss it is determined by the function itself,maybe in the kernel functions there is some different declare manners.Thanks again.

    I think it may just be the functions you looked at.

    There are several ways to return from a function in ARM/Thumb.  The most common (at least in my experience) are "BX lr" and "LDM sp!, {...., sp}".  Although the second one often gets written as "PUSH {....., pc}" depends on which tools you are using.  I suspect if you kept looking long enough you would find examples of each in both the kernel and the app.

    The "B ..." is a little more interesting.  I suspect that this is a compiler optimization called "tail calling" - again there is no reason why you this couldn't be present in both the kernel and the app.  http://en.wikipedia.org/wiki/Tail_call
Reply
  • Note: This was originally posted on 29th August 2012 at http://forums.arm.com

    Thank you very much.

    Besides that two ways you said,an uncommon way is :Mov pc,XX.  The compiler is not intelligent,so there must be reason using different ways to return.I guss it is determined by the function itself,maybe in the kernel functions there is some different declare manners.Thanks again.

    I think it may just be the functions you looked at.

    There are several ways to return from a function in ARM/Thumb.  The most common (at least in my experience) are "BX lr" and "LDM sp!, {...., sp}".  Although the second one often gets written as "PUSH {....., pc}" depends on which tools you are using.  I suspect if you kept looking long enough you would find examples of each in both the kernel and the app.

    The "B ..." is a little more interesting.  I suspect that this is a compiler optimization called "tail calling" - again there is no reason why you this couldn't be present in both the kernel and the app.  http://en.wikipedia.org/wiki/Tail_call
Children
No data