Re: [PATCH v1 1/1] arch: microblaze: allocate stack space for register params

[Gopi Kumar Bulusu]

namaskaaram

Yes, please refer to Microblaze Processor Reference Guide, ABI section

https://docs.amd.com/r/en-US/ug984-vivado-microblaze-ref/Stack-Convention

dhanyavaadaaha
gopi

Sankhya Technologies
www.sankhya.com

On Tue, Apr 21, 2026 at 4:16 PM Frager, Neal <neal.frager@xxxxxxx> wrote:
>
> [AMD Official Use Only - AMD Internal Distribution Only]
>
> Hi Gopi
>
> > There should be 4 bytes for return address (place for link register) as well.
>
> I tested with 24 bytes and I boot normally with your patch and gcc v15.
> #define SYSCALL_ARGS_SIZE 24
>
> If you are sure 28 bytes are needed, I will make the patch 28 with a comment
> explaining the 6 argument registers plus the link register.
>
> > Hi Michal,
>
> > Thank you for your thorough review.
>
> > C functions are invoked with arguments without allocating stack space for
> > register params (for potential register spills). As a result kernel built
> > with gcc v15 boot hangs at the point of starting init -.
>
> > Remove -.
>
> > Fixed for v2.
>
> >
> > This patch adds necessary stack space for few C function calls from entry.S
>
> > Add necessary.
>
> > Fixed for v2.
>
> > (not all). After this patch, the kernel boots all the way to login prompt and
> > root login works. Simple commands like ps work and show normal output.
> >
> > Signed-off-by: Gopi Kumar Bulusu <mailto:gopi@xxxxxxxxxxx>
> > Tested-by: Neal Frager <mailto:neal.frager@xxxxxxx>
>
> > If you are sending it you should have sob line here.
>
> > Fixed for v2.
>
> > ---
> >   arch/microblaze/kernel/entry.S | 20 ++++++++++++++------
> >   1 file changed, 14 insertions(+), 6 deletions(-)
> >
> > diff --git a/arch/microblaze/kernel/entry.S b/arch/microblaze/kernel/entry.S
> > index 582d7256d815..2f9604640486 100644
> > --- a/arch/microblaze/kernel/entry.S
> > +++ b/arch/microblaze/kernel/entry.S
> > @@ -339,6 +339,9 @@ C_ENTRY(mb_invalidate_icache):
> >    * Trap entered via brki instruction, so BIP bit is set, and interrupts
> >    * are masked. This is nice, means we don't have to CLI before state save
> >    */
> > +
> > +#define SYSCALL_ARGS_SIZE 36
>
> > I am testing if 36 is really needed and am running a test using 24
> > for the 6 registers that are used for arguments.
>
> > +
> >   C_ENTRY(_user_exception):
> >       swi     r1, r0, TOPHYS(PER_CPU(ENTRY_SP)) /* save stack */
> >       addi    r14, r14, 4     /* return address is 4 byte after call */
> > @@ -422,16 +425,19 @@ C_ENTRY(_user_exception):
> >       lwi     r12, r12, sys_call_table
> >       /* where the trap should return need -8 to adjust for rtsd r15, 8 */
> >       addi    r15, r0, ret_from_trap-8
> > +     addik   r1, r1, -SYSCALL_ARGS_SIZE
>
> > Please check coding style here.
>
> > Fixed for v2.
>
> > I will test it on real HW and will talk to you directly about results.
>
> > Yes please.  Thank you!
>
> Best regards,
> Neal Frager
> AMD