From: Luis Machado <luis.machado@arm.com>
To: Mark Wielaard <mark@klomp.org>, noloader@gmail.com
Cc: Gdb <gdb@sourceware.org>, Binutils <binutils@sourceware.org>
Subject: Re: buildbot vs --enable-targets=all
Date: Wed, 3 Aug 2022 12:54:13 +0100 [thread overview]
Message-ID: <c7294566-1fb6-08ed-be41-ddb9e8a32a08@arm.com> (raw)
In-Reply-To: <62a77a3a304f0088fe75adfb2b2ce3339023a32a.camel@klomp.org>
On 8/3/22 12:49, Mark Wielaard wrote:
> Hi Luis,
>
> On Wed, 2022-08-03 at 12:35 +0100, Luis Machado wrote:
>> On 8/3/22 11:38, Mark Wielaard wrote:
>>> On Mon, 2022-07-25 at 21:59 -0400, Jeffrey Walton wrote:
>>>> On Mon, Jul 25, 2022 at 8:26 AM Mark Wielaard <mark@klomp.org>
>>>> wrote:
>>>>> On fedora-s390x and debian-ppc64 one of the gdb selftests fails
>>>>> https://builder.sourceware.org/buildbot/#builders/75/builds/783
>>>>> https://builder.sourceware.org/buildbot/#builders/76/builds/772
>>>>>
>>>>> Running selftest arm-record.
>>>>> Process record and replay target doesn't support syscall number
>>>>> -2036195
>>>>> Process record does not support instruction 0x7f70ee1d at
>>>>> address 0x0.
>>>>> Self test failed: self-test failed at ../../binutils-
>>>>> gdb/gdb/arm-
>>>>> tdep.c:14407
>>>>>
>>>>> Which is:
>>>>>
>>>>> /* 32-bit Thumb-2 instructions. */
>>>>> {
>>>>> arm_insn_decode_record arm_record;
>>>>>
>>>>> memset (&arm_record, 0, sizeof (arm_insn_decode_record));
>>>>> arm_record.gdbarch = gdbarch;
>>>>>
>>>>> static const uint16_t insns[] = {
>>>>> /* 1d ee 70 7f mrc 15, 0, r7, cr13, cr0, {3} */
>>>>> 0xee1d, 0x7f70,
>>>>> };
>>>>>
>>>>> enum bfd_endian endian = gdbarch_byte_order_for_code
>>>>> (arm_record.gdbarch);
>>>>> instruction_reader_thumb reader (endian, insns);
>>>>> int ret = decode_insn (reader, &arm_record, THUMB2_RECORD,
>>>>> THUMB2_INSN_SIZE_BYTES);
>>>>>
>>>>> SELF_CHECK (ret == 0);
>>>>> SELF_CHECK (arm_record.mem_rec_count == 0);
>>>>> SELF_CHECK (arm_record.reg_rec_count == 1);
>>>>> SELF_CHECK (arm_record.arm_regs[0] == 7);
>>>>> }
>>>>>
>>>>> This seems a big endian issue given the instructions are given
>>>>> as two
>>>>> 16bit numbers.
>>>>
>>>> [...]
>>>>> For ARM, this does not look right (to me):
>>>>> static const uint16_t insns[] = {
>>>>> /* 1d ee 70 7f mrc 15, 0, r7, cr13, cr0, {3} */
>>>>> 0xee1d, 0x7f70,
>>>>> };
>>>>
>>>> I think you are supposed to use .inst.n and .inst.w because they
>>>> handle endianness properly.
>>>
>>> I couldn't figure out how to do that. Could you give an example?
>>> It looks like the instruction_reader_thumb only takes an array of
>>> uint16_t (even though the instructions are 32bit long). But I might
>>> be
>>> looking at the wrong code.
>>>
>>> So the following fixes it for me on s390x and ppc64
>>>
>>> diff --git a/gdb/arm-tdep.c b/gdb/arm-tdep.c
>>> index d4c5beb5e06..ef0da73398d 100644
>>> --- a/gdb/arm-tdep.c
>>> +++ b/gdb/arm-tdep.c
>>> @@ -14471,7 +14471,7 @@ arm_record_test (void)
>>>
>>> static const uint16_t insns[] = {
>>> /* 1d ee 70 7f mrc 15, 0, r7, cr13, cr0, {3} */
>>> - 0xee1d, 0x7f70,
>>> + 0x7f70, 0xee1d,
>>> };
>>>
>>> enum bfd_endian endian = gdbarch_byte_order_for_code
>>> (arm_record.gdbarch);
>>>
>>> But obviously that breaks things on little-endian architectures.
>>> We could define the insns[] differently using
>>>
>>> #if _BYTE_ORDER == _LITTLE_ENDIAN
>>> 0xee1d, 0x7f70,
>>> #else
>>> 0x7f70, 0xee1d,
>>> #endif
>>>
>>> But that might not be what you meant.
>>>
>> I wonder what's going wrong here given we're using
>> gdbarch_byte_order_for_code to read things.
>>
>> Technically it should read in the right order.
>
> Yes, if the code bytes were in the right order. Like when you read them
> from disk or from a process running in that byte order. But here they
> are constructed in memory in the byte order of the host architecture as
> an uint16_t array. So when using the gdbarch_byte_order_for_code order
> to reconstruct those instructions it is not using the host byte order
> (if they don't match).
>
> I think what Jeffrey means is that there is a different way to
> construct the bytes in memory using .inst.n and .inst.w, but I don't
> fully understand how that works.
>
> Cheers,
>
> Mark
Ah, I see. And s390/ppc being potentially big endian, this fails.
I managed to reproduce this on my end by forcing GDB to use big endian. Could you please file a PR for this one and cc me?
I'll try to come up with a fix.
next prev parent reply other threads:[~2022-08-03 11:54 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-07-25 12:25 Mark Wielaard
2022-07-26 1:24 ` Alan Modra
2022-07-26 11:46 ` Alan Modra
2022-07-26 12:43 ` Alan Modra
2022-07-26 12:55 ` Mark Wielaard
2022-07-26 1:59 ` Jeffrey Walton
2022-08-03 10:38 ` Mark Wielaard
2022-08-03 10:56 ` Andreas Schwab
2022-08-03 11:35 ` Luis Machado
2022-08-03 11:49 ` Mark Wielaard
2022-08-03 11:54 ` Luis Machado [this message]
2022-08-03 11:57 ` Mark Wielaard
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