From: Jan Beulich <jbeulich@suse.com>
To: Oleksii <oleksii.kurochko@gmail.com>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>,
George Dunlap <george.dunlap@citrix.com>,
Julien Grall <julien@xen.org>,
Stefano Stabellini <sstabellini@kernel.org>, Wei Liu <wl@xen.org>,
xen-devel@lists.xenproject.org
Subject: Re: [PATCH v1 1/4] xen: introduce CONFIG_GENERIC_BUG_FRAME
Date: Thu, 16 Feb 2023 15:55:57 +0100 [thread overview]
Message-ID: <ae76d2d6-486a-8717-d02b-5431709a0922@suse.com> (raw)
In-Reply-To: <413b6d1439a31e24719321494971cc165bd6942c.camel@gmail.com>
On 16.02.2023 11:44, Oleksii wrote:
> On Thu, 2023-02-16 at 08:31 +0100, Jan Beulich wrote:
>> On 15.02.2023 18:59, Oleksii wrote:
>>> 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()?)
> Hmm. I don't know other ways to express an immediate operand except
> 'i'.
>
> It looks like type, line, msg are always 'constants'
> (
> they possibly can be passed without 'i' and used directly inside asm():
> ...
> ".pushsection .bug_frames." __stringify(type) ", \"a\",
> %progbits\n"\
> ...
> ) but the issue will be with 'ptr' for which we have to use 'i'.
>
> And I am not sure about all 'constants'. For example, I think that it
> can be an issue with 'line' = '((line & ((1 << BUG_LINE_LO_WIDTH) - 1))
> << BUG_DISP_WIDTH)' if we will use that directly inside asm(...).
Not matter how complex an expression, the compiler will evaluate it to
a plain number if it's a constant expression. The only think to worry
about with "i" is, as said, is the value supplied is the address of
some symbol (or an expression involving such).
Jan
next prev parent reply other threads:[~2023-02-16 14:56 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-02-03 17:05 [PATCH v1 0/4] introduce generic implementation of macros from bug.h Oleksii Kurochko
2023-02-03 17:05 ` [PATCH v1 1/4] xen: introduce CONFIG_GENERIC_BUG_FRAME Oleksii Kurochko
2023-02-13 12:24 ` Jan Beulich
2023-02-13 13:19 ` Julien Grall
2023-02-13 13:30 ` Jan Beulich
2023-02-13 13:56 ` Julien Grall
2023-02-13 15:02 ` Jan Beulich
2023-02-13 15:07 ` Julien Grall
2023-02-13 15:14 ` Jan Beulich
2023-02-13 13:33 ` Andrew Cooper
2023-02-13 13:55 ` Julien Grall
2023-02-14 16:22 ` Oleksii
2023-02-14 16:55 ` Jan Beulich
2023-02-15 15:06 ` Oleksii
2023-02-15 17:59 ` Oleksii
2023-02-16 7:31 ` Jan Beulich
2023-02-16 10:44 ` Oleksii
2023-02-16 12:09 ` Oleksii
2023-02-16 12:19 ` Andrew Cooper
2023-02-16 20:44 ` Oleksii
2023-02-17 7:12 ` Jan Beulich
2023-02-17 9:33 ` Oleksii
2023-02-16 14:55 ` Jan Beulich [this message]
2023-02-16 10:48 ` Andrew Cooper
2023-02-16 12:21 ` Oleksii
2023-02-16 14:53 ` Jan Beulich
2023-02-03 17:05 ` [PATCH v1 2/4] xen/arm: switch ARM to use generic implementation of bug.h Oleksii Kurochko
2023-02-13 13:02 ` Jan Beulich
2023-02-14 16:28 ` Oleksii
2023-02-03 17:05 ` [PATCH v1 3/4] xen/x86: switch x86 to use generic implemetation " Oleksii Kurochko
2023-02-13 13:10 ` Jan Beulich
2023-02-14 16:41 ` Oleksii
2023-02-03 17:05 ` [PATCH v1 4/4] xen: change <asm/bug.h> to <xen/bug.h> Oleksii Kurochko
2023-02-13 13:13 ` Jan Beulich
2023-02-14 16:44 ` Oleksii
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