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Re: [PATCH v13 1/2] xen/riscv: enable GENERIC_BUG_FRAME
- To: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Wed, 7 Aug 2024 16:39:14 +0200
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- Cc: Alistair Francis <alistair.francis@xxxxxxx>, Bob Eshleman <bobbyeshleman@xxxxxxxxx>, Connor Davis <connojdavis@xxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Wed, 07 Aug 2024 14:39:37 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 06.08.2024 18:37, Oleksii Kurochko wrote:
> Enable GENERIC_BUG_FRAME to support BUG(), WARN(), ASSERT,
> and run_in_exception_handler().
>
> "UNIMP" is used for BUG_INSTR, which, when macros from <xen/bug.h>
> are used, triggers an exception with the ILLEGAL_INSTRUCTION cause.
> This instruction is encoded as a 2-byte instruction when
> CONFIG_RISCV_ISA_C is enabled:
> ffffffffc0046ba0: 0000 unimp
> and is encoded as a 4-byte instruction when CONFIG_RISCV_ISA_C
> ins't enabled:
> ffffffffc005a460: c0001073 unimp
>
> Using 'ebreak' as BUG_INSTR does not guarantee proper handling of macros
> from <xen/bug.h>. If a debugger inserts a breakpoint (using the 'ebreak'
> instruction) at a location where Xen already uses 'ebreak', it
> creates ambiguity. Xen cannot distinguish whether the 'ebreak'
> instruction is inserted by the debugger or is part of Xen's own code.
>
> Remove BUG_INSN_32 and BUG_INSN_16 macros as they encode the ebreak
> instruction, which is no longer used for BUG_INSN.
>
> Update the comment above the definition of INS_LENGTH_MASK as instead of
> 'ebreak' instruction 'unimp' instruction is used.
>
> <xen/lib.h> is included for the reason that panic() and printk() are
> used in common/bug.c and RISC-V fails if it is not included.
>
> Signed-off-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
Just one more (cosmetic) question:
> --- a/xen/arch/riscv/include/asm/bug.h
> +++ b/xen/arch/riscv/include/asm/bug.h
> @@ -9,7 +9,7 @@
>
> #ifndef __ASSEMBLY__
>
> -#define BUG_INSTR "ebreak"
> +#define BUG_INSTR "UNIMP"
Deliberately all uppercase?
Jan
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