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

Eric Christopher echristo at gmail.com
Tue Sep 16 17:55:26 PDT 2014 

On Tue, Sep 16, 2014 at 5:53 PM, Akira Hatanaka <ahatanak at gmail.com> wrote:

> 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?
>

Seems like a reasonable way to go yes?

-eric


>
> -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>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> _______________________________________________
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>>>>>>>>>> cfe-commits at cs.uiuc.edu
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>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>> _______________________________________________
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>>>>>
>>>>
>>>
>>
>
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