From: Jan Beulich <jbeulich@suse.com>
To: Julien Grall <julien@xen.org>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>,
Stefano Stabellini <sstabellini@kernel.org>,
Gianluca Guida <gianluca@rivosinc.com>,
Bob Eshleman <bobbyeshleman@gmail.com>,
Alistair Francis <alistair.francis@wdc.com>,
Connor Davis <connojdavis@gmail.com>,
Oleksii <oleksii.kurochko@gmail.com>,
xen-devel@lists.xenproject.org
Subject: Re: [PATCH v2 12/14] xen/riscv: introduce an implementation of macros from <asm/bug.h>
Date: Thu, 2 Feb 2023 12:50:38 +0100 [thread overview]
Message-ID: <3c649ad7-ddee-8a3f-485b-3e056f1e9c73@suse.com> (raw)
In-Reply-To: <b5dba106-e7ed-4aa9-ea44-19adacc7fade@xen.org>
On 01.02.2023 23:11, Julien Grall wrote:
> On 01/02/2023 17:40, Oleksii wrote:
>> I wrote the following macros and they have been compiled without any
>> errors:
>> .....
>> #define _ASM_BUGFRAME_TEXT(second_frame) \
>> ".Lbug%=: ebreak\n" \
>> ".pushsection .bug_frames.%c[bf_type], \"a\", @progbits\n" \
>> ".p2align 2\n" \
>> ".Lfrm%=:\n" \
>> ".long (.Lfrm%=)\n" \
>> ".long (0x55555555)\n" \
>> ".long (.Lbug%=)\n" \
>> ".long (0x55555555)\n" \
>> ".long %c[bf_line_hi]\n" \
>> ".long (0x55555555)\n" \
>> ".long %[bf_line_hi]\n" \
>> ".long (0x55555555)\n" \
>> ".long %[bf_line_lo]\n" \
>> ".long (0x55555555)\n" \
>> ".long %[bf_ptr]\n" \
>> ".long (0x55555555)\n" \
>> ".long (.Lbug%= - .Lfrm%=) + %c[bf_line_hi]\n" \
>> ".popsection\n" \
>>
>> #define _ASM_BUGFRAME_INFO(type, line, ptr, msg) \
>> [bf_type] "i" (type), \
>> [bf_ptr] "i" (ptr), \
>> [bf_msg] "i" (msg), \
>> [bf_line_lo] "i" ((line & ((1 << BUG_LINE_LO_WIDTH) - 1)) \
>> << BUG_DISP_WIDTH), \
>> [bf_line_hi] "i" (((line) >> BUG_LINE_LO_WIDTH) << BUG_DISP_WIDTH)
>>
>> #define BUG_FRAME(type, line, ptr, second_frame, msg) do { \
>> __asm__ __volatile__ ( _ASM_BUGFRAME_TEXT(second_frame) \
>> :: _ASM_BUGFRAME_INFO(type, line, ptr, msg) ); \
>> } while (0)
>> ....
>>
>>
>> But if add ".long %c[bf_ptr]\n" then the following compilation error
>> will occur: [ error: invalid 'asm': invalid use of '%c'. ]
>>
>> If you look at the dissembler of _bug_frames_...
>> ......
>> 80201010: 1010 addi a2,sp,32 # .Lfrm%=
>> 80201012: 8020 .2byte 0x8020
>> 80201014: 5555 li a0,-11
>> 80201016: 5555 li a0,-11
>> 80201018: 3022 .2byte 0x3022 # .Lbug%=
>> 8020101a: 8020 .2byte 0x8020
>> 8020101c: 5555 li a0,-11
>> 8020101e: 5555 li a0,-11
>> 80201020: 0000 unimp # %c[bf_line_hi]
>> 80201022: 0000 unimp
>> 80201024: 5555 li a0,-11
>> 80201026: 5555 li a0,-11
>> 80201028: 0000 unimp # %[bf_line_hi]
>> 8020102a: 0000 unimp
>> 8020102c: 5555 li a0,-11
>> 8020102e: 5555 li a0,-11
>> 80201030: 0000 unimp # %[bf_line_lo]
>> 80201032: 1600 addi s0,sp,800
>> 80201034: 5555 li a0,-11
>> 80201036: 5555 li a0,-11
>> 80201038: 10b8 addi a4,sp,104 # %[bf_ptr]
>> 8020103a: 8020 .2byte 0x8020
>> 8020103c: 5555 li a0,-11
>> 8020103e: 5555 li a0,-11
>> 80201040: 2012 .2byte 0x2012 # (.Lbug%= -
>> .Lfrm%=) + %c[bf_line_hi]
>> .....
>> ... it looks like the error will be generated if the name in %c[name]
>> isn't equal to 0.
>>
>> Another thing I noticed is that %[name] can be used instead of %c[name]
>> for RISC-V ( i did a quick check and it works) so it is still possible
>> to follow Intel implementation but required a redefinition of
>> _ASM_BUGFRAME_TEXT where %c[...] won't be used. All the rest will be
>> the same as in x86 implementation:
>> .....
>> #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" \
>> .....
>>
>> One thing I would like to ask you is why it's better to follow/use x86
>> implementation instead of ARM?
>
> IMHO, the x86 version is cleaner. But...
>
>> It seems that "%c[...]" has the best support only for Intel GCC and
>> thereby ARM implementation looks more universal, doesn't it?
>
> ... you are right, the Arm version is more portable. Although, I do
> wonder how GCC managed to have a different behavior between architecture
> as I would have expected %c to be a generic implementation.
While the implementation is common, the condition when 'c' is legitimate
can be customized by arch-specific code. While all code for all of the
four architectures does so, perhaps x86'es goes farther with what it
permits.
Jan
next prev parent reply other threads:[~2023-02-02 11:51 UTC|newest]
Thread overview: 54+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-27 13:59 [PATCH v2 00/14] RISCV basic exception handling implementation Oleksii Kurochko
2023-01-27 13:59 ` [PATCH v2 01/14] xen/riscv: add _zicsr to CFLAGS Oleksii Kurochko
2023-01-31 0:21 ` Alistair Francis
2023-01-31 9:14 ` Jan Beulich
2023-02-06 16:09 ` Oleksii
2023-01-27 13:59 ` [PATCH v2 02/14] xen/riscv: add <asm/asm.h> header Oleksii Kurochko
2023-01-31 0:49 ` Alistair Francis
2023-02-06 16:22 ` Oleksii
2023-01-27 13:59 ` [PATCH v2 03/14] xen/riscv: add <asm/riscv_encoding.h header Oleksii Kurochko
2023-01-30 13:29 ` Alistair Francis
2023-01-27 13:59 ` [PATCH v2 04/14] xen/riscv: add <asm/csr.h> header Oleksii Kurochko
2023-01-27 14:10 ` Jan Beulich
2023-01-30 11:37 ` Oleksii
2023-01-30 13:26 ` Alistair Francis
2023-01-27 13:59 ` [PATCH v2 05/14] xen/riscv: introduce empty <asm/string.h> Oleksii Kurochko
2023-01-31 0:49 ` Alistair Francis
2023-01-27 13:59 ` [PATCH v2 06/14] xen/riscv: introduce empty <asm/cache.h> Oleksii Kurochko
2023-01-31 0:50 ` Alistair Francis
2023-01-27 13:59 ` [PATCH v2 07/14] xen/riscv: introduce exception context Oleksii Kurochko
2023-01-27 14:24 ` Jan Beulich
2023-01-30 11:54 ` Oleksii
2023-01-30 13:50 ` Jan Beulich
2023-01-30 22:44 ` Julien Grall
2023-02-01 2:27 ` Andrew Cooper
2023-02-01 1:30 ` Stefano Stabellini
2023-02-06 17:13 ` Oleksii
2023-01-27 14:54 ` Julien Grall
2023-01-30 11:40 ` Oleksii
2023-01-30 22:11 ` Julien Grall
2023-01-31 12:24 ` Oleksii
2023-01-31 12:39 ` Julien Grall
2023-01-27 13:59 ` [PATCH v2 08/14] xen/riscv: introduce exception handlers implementation Oleksii Kurochko
2023-01-27 13:59 ` [PATCH v2 09/14] xen/riscv: introduce decode_cause() stuff Oleksii Kurochko
2023-01-27 13:59 ` [PATCH v2 10/14] xen/riscv: mask all interrupts Oleksii Kurochko
2023-01-27 13:59 ` [PATCH v2 11/14] xen/riscv: introduce trap_init() Oleksii Kurochko
2023-01-27 13:59 ` [PATCH v2 12/14] xen/riscv: introduce an implementation of macros from <asm/bug.h> Oleksii Kurochko
2023-01-27 14:34 ` Jan Beulich
2023-01-30 11:23 ` Oleksii
2023-01-27 14:38 ` Jan Beulich
2023-01-27 16:02 ` Julien Grall
2023-01-30 11:35 ` Oleksii
2023-01-30 11:49 ` Juergen Gross
2023-01-30 22:28 ` Julien Grall
2023-01-31 12:34 ` Oleksii
2023-02-01 17:40 ` Oleksii
2023-02-01 22:11 ` Julien Grall
2023-02-02 11:50 ` Jan Beulich [this message]
2023-02-03 13:15 ` Oleksii
2023-02-03 13:23 ` Julien Grall
2023-02-03 16:25 ` Oleksii
2023-01-27 13:59 ` [PATCH v2 13/14] xen/riscv: test basic handling stuff Oleksii Kurochko
2023-01-27 13:59 ` [PATCH v2 14/14] automation: add smoke test to verify macros from bug.h Oleksii Kurochko
2023-01-27 14:43 ` Michal Orzel
2023-01-30 11:15 ` Oleksii
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