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

Thu Sep 18 11:17:57 PDT 2014

The attached patch is a follow-up to r217994. I defined a new function
validateOperandSize, which is used to check both input and output sizes.

On Tue, Sep 16, 2014 at 6:07 PM, Eric Christopher <echristo at gmail.com>
wrote:

> 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>
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>> _______________________________________________
>>>>>>>>>>>>> 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
>>>>>>>>
>>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>>
>
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