[PATCH] x86 inline-asm: error-out on a 64-bit variable bound to a single register in 32-bit mode

Akira Hatanaka ahatanak at gmail.com
Tue Sep 16 17:53:33 PDT 2014 

On Tue, Sep 16, 2014 at 5:12 PM, Eric Christopher <echristo at gmail.com>
wrote:

>
>
> On Tue, Sep 16, 2014 at 4:00 PM, Akira Hatanaka <ahatanak at gmail.com>
> wrote:
>
>> On Tue, Sep 16, 2014 at 1:06 PM, Eric Christopher <echristo at gmail.com>
>> wrote:
>>
>>> You'll want to split out the new contraints for input size into a
>>> separate patch. (And just commit it).
>>> A small comment of why we're ignoring dependent types would be good.
>>>
>>> One question: Why not just add all of the contraints first rather than
>>> piecemeal as you get testcases? (Related to the comment above).
>>>
>>>
>> Just to make sure I'm not misunderstanding your question, are you
>> suggesting I use "=abcdSD" instead of "=a" in the test case and do the
>> check in one line?
>>
>> uint64_t val;
>>
>> __asm__ volatile("addl %1, %0" : "=abcdSD" (val) : "a" (msr)); //
>> expected-error {{invalid output size for constraint '=abcdSD'}}
>>
>>
>> Are you also suggesting that we should have clang print just the
>> constraints that are invalid in the error message? For example, if we added
>> "A" and use "=abcdSDA" instead, clang would remove "A", since it can be
>> bound to a 64-bit variable, and print  "=abcdSD" or "abcdSD" instead?
>>
>>
>>
> No, I'm curious why you're adding S and D now, but not any other
> constraint that has a size associated with the register.
>
>
OK, I see. I just felt that S and D should be added too, since they are
single register constraints that have to be bound to variables smaller than
64-bit, as constraints a-d are.

I can probably add R, q, Q, to the switch-case statement too. Also, in my
next patch, I was going to add checks for constraints x and y.

Should I add the all the constraints I mentioned above to
X86_32TargetInfo::validateInputSize or X86TargetInfo::validateInputSize
first and then add the checks for output constraints?

-eric
>
>
>>
>> Thanks!
>>>
>>> -eric
>>>
>>> On Fri Aug 29 2014 at 4:46:37 PM Akira Hatanaka <ahatanak at gmail.com>
>>> wrote:
>>>
>>>> Does the latest patch look fine? I am working on another patch which
>>>> fixes a similar bug and I need to commit this patch first.
>>>>
>>>>
>>>> On Thu, Aug 28, 2014 at 10:08 AM, Akira Hatanaka <ahatanak at gmail.com>
>>>> wrote:
>>>>
>>>>> Latest version of the patch is attached which fixes a couple of
>>>>> oversights. I had to add a line which checks whether Ty is a dependent type
>>>>> before getTypeSize is called. Also, in the test case, "=" was missing
>>>>> before constraint "a", so fixed that too.
>>>>>
>>>>> On Wed, Aug 27, 2014 at 3:22 PM, Reid Kleckner <rnk at google.com> wrote:
>>>>>
>>>>>> New patch looks good to me.
>>>>>>
>>>>>> It sounds like we have two cases of size mismatch:
>>>>>> - The output operand lvalue is smaller than the constraint, meaning
>>>>>> the store will write out of bounds. Your patch adds this.
>>>>>> - The output operand lvalue is bigger than the constraint, meaning
>>>>>> the whole value won't be initialized. We currently warn here via
>>>>>> validateConstraintModifier.
>>>>>>
>>>>>> This code probably deserves some cleanup, but your patch is
>>>>>> consistent with what we do for input operands, so let's go with that.
>>>>>>
>>>>>>
>>>>> The reason llvm is crashing in the backend is that it's trying to use
>>>>> a 64-bit register in 32-bit mode. It's not because a store is writing out
>>>>> of bounds or there is a value left uninitialized. In the test case, if we
>>>>> declare the variable bound to constraint "=a" to be a unit32_t or an
>>>>> integer type that is smaller than 32-bit, clang compiles the program fine.
>>>>>
>>>>>
>>>>>>
>>>>>> On Wed, Aug 27, 2014 at 12:35 PM, Akira Hatanaka <ahatanak at gmail.com>
>>>>>> wrote:
>>>>>>
>>>>>>> The commit log in r166737 doesn't say much about why this is a
>>>>>>> warning instead of an error, but I know there are cases where warnings are
>>>>>>> needed. For example, clang has to issue warnings instead of errors for the
>>>>>>> inline-asm statements in the test case committed in r216260. If it's not
>>>>>>> desirable to change validateConstraintModifier, we can add a function which
>>>>>>> checks the output size that is similar to validateInputSize in r167717 (see
>>>>>>> attached patch), which was suggested in the post-commit review.
>>>>>>>
>>>>>>>
>>>>>>> http://lists.cs.uiuc.edu/pipermail/cfe-commits/Week-of-Mon-20121112/067945.html
>>>>>>>
>>>>>>> I am not sure whether we can use fixit in this case. Fixit hints
>>>>>>> should be used only if we know the user's intent and it's very clear that
>>>>>>> applying the fixit hint is the right thing to do. Changing the type of
>>>>>>> variable "r" to a 32-bit int will avoid crashing, but it doesn't look like
>>>>>>> that's what the user wants.
>>>>>>>
>>>>>>> On Mon, Aug 25, 2014 at 6:20 PM, Reid Kleckner <rnk at google.com>
>>>>>>> wrote:
>>>>>>>
>>>>>>>> Can you investigate why we are warning in the first place? I think
>>>>>>>> we should either only warn or only error. Currently we have a warning with
>>>>>>>> a fixit but we don't recover as though we had applied the fixit. If we did
>>>>>>>> that, we would not crash.
>>>>>>>>
>>>>>>>> In addition to the Clang-side changes, LLVM should probably be
>>>>>>>> returning an error or reporting a fatal error instead of hitting
>>>>>>>> unreachable.
>>>>>>>>
>>>>>>>>
>>>>>>>>  On Mon, Aug 25, 2014 at 2:10 PM, Akira Hatanaka <
>>>>>>>> ahatanak at gmail.com> wrote:
>>>>>>>>
>>>>>>>>>  Rebased patches attached.
>>>>>>>>>
>>>>>>>>> I also made changes to the clang patch so that clang can error-out
>>>>>>>>> after a size mismatch is found as soon as
>>>>>>>>> possible.TargetInfo::validateConstraintModifier has an extra parameter
>>>>>>>>> IsError, which is set when it decides there is no point in continuing
>>>>>>>>> compilation and it should stop compilation immediately. The error message
>>>>>>>>> clang prints looks better than lllvm's message, but if it isn't right to
>>>>>>>>> change the warning to an error, then I guess we have to detect the error
>>>>>>>>> later just before isel, as is done in the llvm patch.
>>>>>>>>>
>>>>>>>>> On Wed, Jul 23, 2014 at 3:56 PM, Akira Hatanaka <
>>>>>>>>> ahatanak at gmail.com> wrote:
>>>>>>>>>
>>>>>>>>>> llvm should error-out when a 64-bit variable is bound to a single
>>>>>>>>>> register in x86 32-bit mode, but ToT clang/llvm fails to detect this error
>>>>>>>>>> and continues compilation until it crashes in type-legalization:
>>>>>>>>>>
>>>>>>>>>> $ llc test/CodeGen/X86/inline-asm-regsize.ll  -O3
>>>>>>>>>> -mtriple=i386-apple-darwin -o -
>>>>>>>>>>
>>>>>>>>>> inline-asm-regsize.ll  -O3 -mtriple=i386-apple-darwin -o -
>>>>>>>>>>
>>>>>>>>>> .section __TEXT,__text,regular,pure_instructions
>>>>>>>>>>
>>>>>>>>>> ExpandIntegerResult #0: 0x7fa2d1041728: i64 = Register %RCX [ID=0]
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> Do not know how to expand the result of this operator!
>>>>>>>>>>
>>>>>>>>>> UNREACHABLE executed at
>>>>>>>>>> /Users/ahatanaka/projects/llvm/git/llvm3/lib/CodeGen/SelectionDAG/LegalizeIntegerTypes.cpp:1116!
>>>>>>>>>>
>>>>>>>>>> The attached patch fixes llvm to error-out and print this error
>>>>>>>>>> message:
>>>>>>>>>>
>>>>>>>>>> error: Cannot bind a variable larger than 32-bit to a single
>>>>>>>>>> register in 32-bit mode
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> My initial solution was to have clang detect this error in
>>>>>>>>>> TargetInfo::validateConstraintModifier. However, the code in
>>>>>>>>>> SemaStmtAsm.cpp has to be changed to error-out instead of issuing a
>>>>>>>>>> warning, which I wasn't sure was the right thing to do. I am attaching this
>>>>>>>>>> patch too in case someone has a suggestion or an opinion on it.
>>>>>>>>>>
>>>>>>>>>> <rdar://problem/17476970>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>> _______________________________________________
>>>>>>>>> cfe-commits mailing list
>>>>>>>>> cfe-commits at cs.uiuc.edu
>>>>>>>>> http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits
>>>>>>>>>
>>>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>>
>>>>>
>>>>>
>>>>>
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>>>
>>
>
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