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

Tue Sep 16 18:07:58 PDT 2014

Cool, thanks.

-eric

On Tue, Sep 16, 2014 at 6:02 PM, Akira Hatanaka <ahatanak at gmail.com> wrote:

> OK, I'll check in a patch that fixes X86_32TargetInfo::validateInputSize
> first then.
>
> On Tue, Sep 16, 2014 at 5:55 PM, Eric Christopher <echristo at gmail.com>
> wrote:
>
>>
>>
>> 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
>>>>>>>>>>>> http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits
>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>> _______________________________________________
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>>>>>>> cfe-commits at cs.uiuc.edu
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>>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>>
>
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