m68k assembly question: jsr vs. bsr

m68k assembly question: jsr vs. bsr

[John Paul Adrian Glaubitz]

Hi!

Can anyone answer this question regarding the difference between "bsr" and "jsr":

> https://github.com/llvm/llvm-project/issues/60354#issuecomment-1412018845

Adrian

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Re: m68k assembly question: jsr vs. bsr

[Geert Uytterhoeven]

Hi Adrian,

On Wed, Feb 1, 2023 at 11:17 PM John Paul Adrian Glaubitz
<glaubitz@physik.fu-berlin.de> wrote:
> Can anyone answer this question regarding the difference between "bsr" and "jsr":
>
> > https://github.com/llvm/llvm-project/issues/60354#issuecomment-1412018845

"jsr" is an absolute jump to a subroutine.
"bsr" is a relative jump (8-bit, 16-bit, or 32-bit signed offset) to a
subroutine,
i.e. typically for calling a nearby function.

There's also "jbsr", which is an assembler macro that picks the most
appropriate: bsr does not need relocation, but bsr.l is 68020+ only.

Gr{oetje,eeting}s,

                        Geert

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Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

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Re: m68k assembly question: jsr vs. bsr

[Andreas Schwab]

On Feb 02 2023, Geert Uytterhoeven wrote:

> Hi Adrian,
>
> On Wed, Feb 1, 2023 at 11:17 PM John Paul Adrian Glaubitz
> <glaubitz@physik.fu-berlin.de> wrote:
>> Can anyone answer this question regarding the difference between "bsr" and "jsr":
>>
>> > https://github.com/llvm/llvm-project/issues/60354#issuecomment-1412018845
>
> "jsr" is an absolute jump to a subroutine.
> "bsr" is a relative jump (8-bit, 16-bit, or 32-bit signed offset) to a
> subroutine,
> i.e. typically for calling a nearby function.

jsr/jmp also take pcrel, but bsr/bra with 8-bit disp is shorter.

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