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

Tue Sep 16 18:02:08 PDT 2014

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>
>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> _______________________________________________
>>>>>>>>>>> cfe-commits mailing list
>>>>>>>>>>> cfe-commits at cs.uiuc.edu
>>>>>>>>>>> http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>> _______________________________________________
>>>>>> cfe-commits mailing list
>>>>>> cfe-commits at cs.uiuc.edu
>>>>>> http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits
>>>>>>
>>>>>
>>>>
>>>
>>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/cfe-commits/attachments/20140916/0e291a98/attachment.html>