Re: [PATCH v1] xen/riscv: make calculation of stack address PC-relative

[Oleksii <oleksii.kurochko@xxxxxxxxx>]

> > 
> > Could you please explain what is x86 section asserts?
> 
> If you look at the bottom of x86's xen.lds.S you'll find a number of
> assertions, among them one towards .got being empty. Some of the
> sections checked there may indeed not be applicable on arbitrary
> architectures, but I think .got is sufficiently universal. So I agree
> with Andrew that it may be worthwhile making some of this generic.

I have question about 'SIZEOF(.got.plt) == 3 * 8':

#ifndef EFI
ASSERT(!SIZEOF(.got),      ".got non-empty")
/*
 * At least GNU ld 2.30 and earlier fail to discard the generic part of
 * .got.plt when no actual entries were allocated. Permit this case
alongside
 * the section being empty.
 */
ASSERT(!SIZEOF(.got.plt) || SIZEOF(.got.plt) == 3 * 8,
       "unexpected .got.plt size")
ASSERT(!SIZEOF(.igot.plt), ".igot.plt non-empty")
ASSERT(!SIZEOF(.iplt),     ".iplt non-empty")
ASSERT(!SIZEOF(.plt),      ".plt non-empty")
ASSERT(!SIZEOF(.rela),     "leftover relocations")
#endif

I assume that the check 'SIZEOF(.got.plt) == 3 * 8' was added to verify
the case when no real entries in .got.plt are needed but .got.plt still
has 3 entries.

I commented the code where got entries are produced now:
--- a/xen/arch/riscv/riscv64/head.S
+++ b/xen/arch/riscv/riscv64/head.S
@@ -20,6 +20,7 @@ ENTRY(start)
         csrc    CSR_SSTATUS, t0
 
         /* Clear the BSS */
+/*
         la      t3, __bss_start
         la      t4, __bss_end
 .L_clear_bss:
@@ -30,5 +31,6 @@ ENTRY(start)
         la     sp, cpu0_boot_stack
         li      t0, STACK_SIZE
         add     sp, sp, t0
+*/
 
         tail    start_xen

And I can't see .got.plt with 3 entries:
  $ riscv64-linux-gnu-objdump -x xen/xen-syms | grep -i got

What am I doing wrong? Or my understanding of the idea of the check is
wrong?

And I assume that add !SIZEOF(.got) and !SIZEOF(.got.plt) would be
enough to RISC-V's xen.lds.S?

~ Oleksii