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

Tue Sep 16 16:00:44 PDT 2014

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?

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