BTW, I do think I need to explicitly set the c++ version in the scons file,
like in Matt's original email above. I'd probably set it to c++14 though,
to be consistent with gem5 proper. I think that will likely fix a build
issue Bobby had with an older (7.x I think) version of gcc, where the
default version is probably different from the compiler I'm using (10.x I
think).
Gabe
On Mon, Nov 9, 2020 at 1:50 PM Gabe Black <gabe.bl...@gmail.com> wrote:
> Hi folks. If you're using the magic address based version of the gem5 ops,
> then you should call, for instance, m5_exit_addr and not just m5_exit. The
> "normal" functions are now always the magic instructions which essentially
> only gem5 CPU models know how to execute. All call mechanisms are built
> into the library at once now so you can use the same binary on the KVM CPU,
> native gem5 CPUs, etc.
>
> You also should not change the scons files when you build. The old
> Makefile based setup required tinkering with things to get the build you
> wanted, but that is no longer necessary. If you need to, that's a bug and
> we should look into it. The lines you're commenting out just set the
> default magic address, and that's only there for legacy reasons. You can
> set the address to use from the command line if you're using the m5
> utility, or by setting the m5op_addr variable if using the library. You
> still have to run map_m5_mem to make the magic physical address visible to
> userspace for the library to work, or otherwise set up a virtual to
> physical mapping if you were, for instance, running in the kernel which
> somebody was doing recently.
>
> If you try to use a call mechanism that isn't supported by your CPU model,
> then the behavior will be unpredictable. For x86 on the KVM CPU for
> example, the special gem5 instructions will do whatever they look like they
> should do on real hardware. That may be a nop, it may be to generate an
> undefined instruction exception, etc. If it's a nop, it will just leave
> whatever is in RAX in RAX.
>
> Also, argument values and return values are now handled by a layer which
> knows and applies the actual ABI rules for a given ISA and for the specific
> types of the arguments and return value. There should be no reason to
> change the code which is calling the pseudo instruction to explicitly set
> RAX, especially if you're using the address based calling mechanism which
> doesn't go through that path at all.
>
> Gabe
>
> On Mon, Nov 9, 2020 at 1:06 PM Matt Sinclair via gem5-users <
> gem5-users@gem5.org> wrote:
>
>> Hi Dan,
>>
>> My comment was just a general comment on the m5ops -- I thought you were
>> using the "old" format for building m5ops and that might have been the
>> problem. Sounds like it wasn't.
>>
>> I think pushing a fix to develop and tagging Gabe and Jason as reviewers
>> is probably the right strategy.
>>
>> Thanks,
>> Matt
>>
>> On Mon, Nov 9, 2020 at 2:33 PM Daniel Gerzhoy <daniel.gerz...@gmail.com>
>> wrote:
>>
>>> I found the issue and fixed it.
>>>
>>> The return value wasn't being put into the Rax register in
>>> src/arch/x86/isa/decoder/two_byte_opcodes.isa
>>>
>>> 0x4: BasicOperate::gem5Op({{
>>> uint64_t ret;
>>> bool recognized =
>>> PseudoInst::pseudoInst<X86PseudoInstABI>(
>>> xc->tcBase(), IMMEDIATE, ret);
>>> if (!recognized)
>>> fault = std::make_shared<InvalidOpcode>();
>>> Rax = ret;
>>>
>>> //<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<Added This
>>> }}, IsNonSpeculative);
>>>
>>> This code was simplified with the new abi stuff and the Rax = ret;
>>> must have been lost in the shuffle.
>>>
>>> I could push the fix to develop, or should I just make an issue on Jira?
>>>
>>> Best,
>>>
>>> Dan
>>>
>>> On Mon, Nov 9, 2020 at 2:50 PM Daniel Gerzhoy <daniel.gerz...@gmail.com>
>>> wrote:
>>>
>>>> Let me further say that I know that the magic instructions are being
>>>> called. I am just getting bogus return values.
>>>>
>>>> On Mon, Nov 9, 2020 at 2:18 PM Daniel Gerzhoy <daniel.gerz...@gmail.com>
>>>> wrote:
>>>>
>>>>> Hi Matt,
>>>>>
>>>>> Thanks for this, it's very helpful. However after following the
>>>>> instructions (I had to extrapolate a little because of the directory
>>>>> structure changes you mentioned) I get the same result: Nill returns from
>>>>> the magic instructions.
>>>>> Actually It isn't nill, but a constant no matter what. If I compile my
>>>>> program with -O0 its nill, if with -O2 its: 4198192, which is suspicious.
>>>>>
>>>>> To clarify, are these updated instructions specifically meant to fix
>>>>> this issue I am running into? Or just general instructions to build m5op.o
>>>>>
>>>>> Here are the specific changes I made according to the link you
>>>>> provided, the supplemental instructions, and extrapolating based on the
>>>>> directory structure change.
>>>>>
>>>>> 1. In SConsopts I commented both:
>>>>>
>>>>> --- a/util/m5/src/abi/x86/SConsopts
>>>>> +++ b/util/m5/src/abi/x86/SConsopts
>>>>> @@ -27,8 +27,8 @@ Import('*')
>>>>>
>>>>> env['ABI'] = 'x86'
>>>>> get_abi_opt('CROSS_COMPILE', '')
>>>>> -env.Append(CXXFLAGS='-DM5OP_ADDR=0xFFFF0000')
>>>>> -env.Append(CCFLAGS='-DM5OP_ADDR=0xFFFF0000')
>>>>> +#env.Append(CXXFLAGS='-DM5OP_ADDR=0xFFFF0000')
>>>>> +#env.Append(CCFLAGS='-DM5OP_ADDR=0xFFFF0000')
>>>>>
>>>>> env['CALL_TYPE']['inst'].impl('m5op.S', 'verify_inst.cc')
>>>>> env['CALL_TYPE']['addr'].impl('m5op_addr.S', default=True)
>>>>>
>>>>> 2. In SConstruct I added:
>>>>>
>>>>> --- a/util/m5/SConstruct
>>>>> +++ b/util/m5/SConstruct
>>>>> @@ -44,7 +44,9 @@ def abspath(d):
>>>>>
>>>>> # Universal settings.
>>>>> main.Append(CXXFLAGS=[ '-O2' ])
>>>>> +main.Append(CXXFLAGS=[ '-std=c++11' ])
>>>>> main.Append(CCFLAGS=[ '-O2' ])
>>>>> main.Append(CPPPATH=[ common_include ])
>>>>>
>>>>> The compilation process compiles m5op.S with gcc though, so c++11
>>>>> doesn't have any effect on it. Not sure if that matters.
>>>>>
>>>>> 3. Finally I linked both m5_mmap.o and m5op.o as per the instructions
>>>>> but I am a little wary of m5_mmap
>>>>>
>>>>> What does m5_mmap actually do if I don't have M5OP_ADDR defined. It
>>>>> looks like nothing? Do I need to link it?
>>>>>
>>>>> *Is there something inside the program I need to do before calling
>>>>> magic instructions that has to do with m5_mmap?*
>>>>>
>>>>> Thanks for your help,
>>>>>
>>>>> Dan
>>>>>
>>>>> On Mon, Nov 9, 2020 at 12:12 PM Matt Sinclair <mattdsincl...@gmail.com>
>>>>> wrote:
>>>>>
>>>>>> Hi Dan,
>>>>>>
>>>>>> In recent weeks, Gabe (if I recall correctly) updated how the m5ops
>>>>>> are created. I had created a homework assignment for my course about it:
>>>>>> https://pages.cs.wisc.edu/~sinclair/courses/cs752/fall2020/handouts/hw3.html
>>>>>> (see #2), but this is now already out of date as the location of some
>>>>>> files
>>>>>> changed. The updated instructions are:
>>>>>>
>>>>>> 1. Update $GEM5_ROOT/util/m5/SConstruct, add a new line between the
>>>>>> current lines 46 and 47:
>>>>>>
>>>>>> main.Append(CXXFLAGS=[ '-O2' ])
>>>>>> *+main.Append(CXXFLAGS=[ '-std=c++11' ])*
>>>>>>
>>>>>> main.Append(CCFLAGS=[ '-O2' ])
>>>>>>
>>>>>> 2. Now run the same command you ran in step 2 of the above link:
>>>>>>
>>>>>> scons build/x86/out/m5
>>>>>>
>>>>>> 3. This will create the same two .o files in step 2 of the above
>>>>>> link, in the same places (although the location of m5op.o may have
>>>>>> changed to include/gem5 util/m5/build/x86/abi/x86/ according to some
>>>>>> of the students in my course).
>>>>>> Matt
>>>>>>
>>>>>> On Mon, Nov 9, 2020 at 9:25 AM Daniel Gerzhoy via gem5-users <
>>>>>> gem5-users@gem5.org> wrote:
>>>>>>
>>>>>>> Hey all,
>>>>>>>
>>>>>>> I've recently updated to using the dev branch for my GCN3
>>>>>>> simulations. I've noticed that I am now getting return values of 0 for
>>>>>>> every magic instruction (m5_rpns for instance).
>>>>>>>
>>>>>>> Is there a special way I need to be compiling/linking m5ops.S to get
>>>>>>> the return values to show up correctly? Or might this be a bug?
>>>>>>>
>>>>>>> Thanks,
>>>>>>>
>>>>>>> Dan
>>>>>>> _______________________________________________
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>>>>>>
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>
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