Re: [PATCH] xen/link: Move SCHEDULER_ARRAY into .rodata

[Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>]

On 11/13/26 8:31 AM, Orzel, Michal wrote:
> On 12-Nov-26 19:36, Andrew Cooper wrote:
> > This is a list of pointers which is only ever read.
> I think that's not true. See sched_test_func() macro in scheduler_init() that
> assigns NULL in case the scheduler does not implement the required hook.
The same happens a few lines below if the scheduler's global_init() fails.

Neither NULL assignment can trigger today (both global_init()
implementations return 0 and all in-tree schedulers provide the
hooks), but I think the writes need dropping first, and the entries want 
to become "const struct sched_ops *const" (both in REGISTER_SCHEDULER() 
and the __{start,end}_schedulers_array declarations) so the compiler 
enforces the property.  It would also be nice to rename .data.schedulers 
to .rodata.schedulers while moving it.
The linker script placement itself looks fine to me.

~ Oleksii
> > In the ARM linker file, fix some adjacent misalignment.
> >
> > Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> > ---
> > CC: Jan Beulich <jbeulich@xxxxxxxx>
> > CC: Roger Pau Monné <roger@xxxxxxxxxxxxxx>
> > CC: Teddy Astie <teddy.astie@xxxxxxxxxx>
> > CC: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> > CC: Julien Grall <julien@xxxxxxx>
> > CC: Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>
> > CC: Bertrand Marquis <bertrand.marquis@xxxxxxx>
> > CC: Michal Orzel <michal.orzel@xxxxxxx>
> > CC: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
> > CC: Baptiste Le Duc <baptiste.le-duc@xxxxxxxxxx>
> > CC: Timothy Pearson <tpearson@xxxxxxxxxxxxxxxxxxxxx>
> > ---
> >   xen/arch/arm/xen.lds.S   | 6 +++---
> >   xen/arch/ppc/xen.lds.S   | 2 +-
> >   xen/arch/riscv/xen.lds.S | 2 +-
> >   xen/arch/x86/xen.lds.S   | 2 +-
> >   4 files changed, 6 insertions(+), 6 deletions(-)
> >
> > diff --git a/xen/arch/arm/xen.lds.S b/xen/arch/arm/xen.lds.S
> > index 613511390ff4..d1bb6c62d208 100644
> > --- a/xen/arch/arm/xen.lds.S
> > +++ b/xen/arch/arm/xen.lds.S
> > @@ -51,9 +51,10 @@ SECTIONS
> >   
> >     . = ALIGN(PAGE_SIZE);
> >     .rodata : {
> > -        _srodata = .;          /* Read-only data */
> > +       _srodata = .;          /* Read-only data */
> >   
> > -        BUGFRAMES
> > +       BUGFRAMES
> > +       SCHEDULER_ARRAY
> >   
> >          *(.rodata)
> >          *(.rodata.*)
> > @@ -93,7 +94,6 @@ SECTIONS
> >     .data : {                    /* Data */
> >          *(.data.page_aligned)
> >   
> > -       SCHEDULER_ARRAY
> >          HYPFS_PARAM
> >   
> >          *(.data .data.*)
> > diff --git a/xen/arch/ppc/xen.lds.S b/xen/arch/ppc/xen.lds.S
> > index 37256c8865a9..cddb70855307 100644
> > --- a/xen/arch/ppc/xen.lds.S
> > +++ b/xen/arch/ppc/xen.lds.S
> > @@ -48,6 +48,7 @@ SECTIONS
> >           _srodata = .;          /* Read-only data */
> >   
> >           BUGFRAMES
> > +        SCHEDULER_ARRAY
> >   
> >           *(.rodata)
> >           *(.rodata.*)
> > @@ -84,7 +85,6 @@ SECTIONS
> >       DECL_SECTION(.data) {                    /* Data */
> >           *(.data.page_aligned)
> >   
> > -        SCHEDULER_ARRAY
> >           HYPFS_PARAM
> >   
> >           *(.data .data.*)
> > diff --git a/xen/arch/riscv/xen.lds.S b/xen/arch/riscv/xen.lds.S
> > index d9375a961697..250ee3f36f4f 100644
> > --- a/xen/arch/riscv/xen.lds.S
> > +++ b/xen/arch/riscv/xen.lds.S
> > @@ -43,6 +43,7 @@ SECTIONS
> >           _srodata = .;          /* Read-only data */
> >   
> >           BUGFRAMES
> > +        SCHEDULER_ARRAY
> >   
> >           *(.srodata)
> >           *(.srodata.*)
> > @@ -91,7 +92,6 @@ SECTIONS
> >       .data : {                    /* Data */
> >           *(.data.page_aligned)
> >   
> > -        SCHEDULER_ARRAY
> >           HYPFS_PARAM
> >   
> >           *(.sdata .sdata.*)
> > diff --git a/xen/arch/x86/xen.lds.S b/xen/arch/x86/xen.lds.S
> > index 8f943e11ead4..925848980219 100644
> > --- a/xen/arch/x86/xen.lds.S
> > +++ b/xen/arch/x86/xen.lds.S
> > @@ -119,6 +119,7 @@ SECTIONS
> >          __ro_after_init_end = .;
> >   
> >          BUGFRAMES
> > +       SCHEDULER_ARRAY
> >   
> >          *(.rodata)
> >          *(.rodata.*)
> > @@ -297,7 +298,6 @@ SECTIONS
> >     DECL_SECTION(.data.read_mostly) {
> >          *(.data.read_mostly)
> >   
> > -       SCHEDULER_ARRAY
> >          HYPFS_PARAM
> >     } PHDR(text)
> >