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Re: [PATCH v1 1/3] xen/riscv: fix switch_stack_and_jump()
- To: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Tue, 19 May 2026 11:28:06 +0200
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- Cc: Baptiste Le Duc <baptiste.le-duc@xxxxxxxxxx>, Alistair Francis <alistair.francis@xxxxxxx>, Connor Davis <connojdavis@xxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Julien Grall <julien@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Tue, 19 May 2026 09:28:11 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 19.05.2026 10:39, Oleksii Kurochko wrote:
> The following compilation issue occurs when UBSAN related stuff is enabled:
> prelink.o: in function `smp_processor_id':
> /build/xen/./arch/riscv/include/asm/current.h:46:(.init.text+0x274e2):
> relocation truncated to fit: R_RISCV_JAL against `init_done'
> make[2]: *** [arch/riscv/Makefile:45: xen-syms] Error 1
There's no init_done() as of yet.
> The switch_stack_and_jump macro uses "j " #fn which assembles to
> JAL x0, init_done is a RISC-V J-type instruction with only ±1MB range.
>
> Without UBSAN, .init.text is small enough that init_done (which lives in
> .text, not .init.text) is within 1MB of the JAL. With UBSAN enabled, all
> the instrumentation calls bloat .init.text well past 1MB, so init_done
> is now >1MB away from the JAL. The linker tries to truncate the 20-bit
> J-type offset and fails.
.init.text is well below 64k right now. Are you telling us that it grows
by more than a factor of 16 when UBSAN is enabled? IOW while the change
may indeed be needed, I question this explanation. .text growth may matter
as well, and e.g. .rodata (living between both sections) might also grow.
Jan
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