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

Thu Sep 18 11:22:45 PDT 2014

LGTM. Thanks!

-eric

On Thu, Sep 18, 2014 at 11:17 AM, Akira Hatanaka <ahatanak at gmail.com> wrote:

> 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
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>>>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>>
>
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