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Re: [PATCH v1 1/4] xen: introduce CONFIG_GENERIC_BUG_FRAME
- To: Oleksii <oleksii.kurochko@xxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Thu, 16 Feb 2023 08:31:35 +0100
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Thu, 16 Feb 2023 07:31:50 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 15.02.2023 18:59, Oleksii wrote:
> Hello Jan and community,
>
> I experimented and switched RISC-V to x86 implementation. All that I
> changed in x86 implementation for RISC-V was _ASM_BUGFRAME_TEXT. Other
> things are the same as for x86.
>
> For RISC-V it is fine to skip '%c' modifier so _ASM_BUGFRAME_TEXT will
> look like:
>
> #define _ASM_BUGFRAME_TEXT(second_frame) \
> ".Lbug%=: ebreak\n"
> ".pushsection .bug_frames.%[bf_type], \"a\", @progbits\n"
> ".p2align 2\n"
> ".Lfrm%=:\n"
> ".long (.Lbug%= - .Lfrm%=) + %[bf_line_hi]\n"
> ".long (%[bf_ptr] - .Lfrm%=) + %[bf_line_lo]\n"
> ".if " #second_frame "\n"
> ".long 0, %[bf_msg] - .Lfrm%=\n"
> ".endif\n"
> ".popsection\n"
I expect this could be further abstracted such that only the actual
instruction is arch-specific.
> The only thing I am worried about is:
>
> #define _ASM_BUGFRAME_INFO(type, line, ptr, msg) \
> [bf_type] "i" (type), ...
> because as I understand it can be an issue with 'i' modifier in case of
> PIE. I am not sure that Xen enables PIE somewhere but still...
> If it is not an issue then we can use x86 implementation as a generic
> one.
"i" is not generally an issue with PIE, it only is when the value is the
address of a symbol. Here "type" is a constant in all cases. (Or else
how would you express an immediate operand of an instruction in an
asm()?)
Jan
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