[PATCH] Ensure proper alignment when reading variadic arguments for x86-32 and x86-64

[Thomas Jablin]

Adding Elena since she most recently touched this function.


On Mon, Jul 28, 2014 at 8:15 AM, Thomas Jablin <tjablin at gmail.com> wrote:

> This patch still requires a reviewer.
>
>
> On Mon, Jul 14, 2014 at 4:07 PM, Thomas Jablin <tjablin at gmail.com> wrote:
>
>> I'm still waiting for a review. This is a patch for PR14792.
>> Tom
>>
>>
>> On Mon, Jun 30, 2014 at 12:34 PM, Thomas Jablin <tjablin at gmail.com>
>> wrote:
>>
>>> I'm still waiting for a review. Maybe Nadav since he owns the x86
>>> backend?
>>>
>>>
>>> On Tue, Jun 24, 2014 at 12:36 PM, Thomas Jablin <tjablin at gmail.com>
>>> wrote:
>>>
>>>> Hi All,
>>>> Please find enclosed an updated and simplified patch along with a
>>>> additional test for properly aligned variadic arguments.
>>>> Tom
>>>>
>>>> On Fri, Jul 19, 2013 at 8:36 PM, Eli Friedman <eli.friedman at gmail.com>
>>>> wrote:
>>>>
>>>>> On Thu, Jul 18, 2013 at 10:31 PM, Yun-Wei Lee <lee2041412 at gmail.com>
>>>>> wrote:
>>>>> > Thank for your suggestion.
>>>>> >
>>>>> > I have tried to use GetAlignedArgumentStackSize.
>>>>> > It is so strange that this function may output uncorrectly.
>>>>> > For example, the StackSize will be 40 when handling the third
>>>>> function call
>>>>> > in main.
>>>>> > If I modified the this function, it will fail one test.
>>>>> > I wonder this may be another bug in llvm......
>>>>> > And that's why I didn't use GetAlignedArgumentStackSize previously.
>>>>> >
>>>>> > Thank you!
>>>>>
>>>>> I'm sorry, I'm not that familiar with the code.  A brief look tells me
>>>>> that it's likely none of the patches are quite right;
>>>>> http://llvm.org/bugs/attachment.cgi?id=10897 looks closer, but still
>>>>> not quite right.
>>>>>
>>>>> -Eli
>>>>>
>>>>> >
>>>>> > On Thu, Jul 18, 2013 at 7:56 PM, Eli Friedman <
>>>>> eli.friedman at gmail.com>
>>>>> > wrote:
>>>>> >>
>>>>> >> On Thu, Jul 18, 2013 at 8:36 AM, Yun-Wei Lee <lee2041412 at gmail.com>
>>>>> wrote:
>>>>> >> > http://llvm.org/bugs/show_bug.cgi?id=14792
>>>>> >> >
>>>>> >> > Problem:
>>>>> >> >   In the i386 ABI Page 3-10, it said that the stack is aligned.
>>>>> However,
>>>>> >> > the
>>>>> >> > two example code show that does not handle the alignment
>>>>> correctly when
>>>>> >> > using variadic function. For example, if the size of the first
>>>>> argument
>>>>> >> > is
>>>>> >> > 17, the overflow_arg_area in va_list will be set to "address of
>>>>> first
>>>>> >> > argument + 16" instead of "address of first argument + 24" after
>>>>> calling
>>>>> >> > va_start.
>>>>> >> >   In addition, #6636 showed the same problem because in AMD64,
>>>>> arguments
>>>>> >> > is
>>>>> >> > passed by register at first, then pass by memory when run out of
>>>>> >> > register
>>>>> >> > (AMD64 ABI 3.5.7 rule 10).
>>>>> >> >
>>>>> >> > Why this problem happened?
>>>>> >> >   When calling va_start to set va_list, overflow_arg_area is not
>>>>> set
>>>>> >> > correctly. To set the overflow_arg_area correctly, we need to get
>>>>> the
>>>>> >> > FrameIndex correctly. Now, here comes the problem, llvm doesn't
>>>>> handle
>>>>> >> > it
>>>>> >> > correctly. It accounts for StackSize to compute the FrameIndex,
>>>>> and if
>>>>> >> > the
>>>>> >> > StackSize is not aligned, it will compute the wrong FrameIndex.
>>>>> As a
>>>>> >> > result
>>>>> >> > overflow_arg_area will not be set correctly.
>>>>> >> >
>>>>> >> > My Solution:
>>>>> >> > 1. Record the Align if it is located in Memory.
>>>>> >> > 2. If it is variadic function and needs to set FrameIndex, adjust
>>>>> the
>>>>> >> > stacksize.
>>>>> >>
>>>>> >> Please read http://llvm.org/docs/DeveloperPolicy.html .  In
>>>>> >> particular, patches should be sent to llvm-commits, and patches
>>>>> should
>>>>> >> generally include a regression test.
>>>>> >>
>>>>> >> In terms of the code, you might want to consider using
>>>>> >> llvm::RoundUpToAlignment.
>>>>> >>
>>>>> >> -Eli
>>>>> >
>>>>> >
>>>>> _______________________________________________
>>>>> LLVM Developers mailing list
>>>>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>>>>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>>>>
>>>>
>>>>
>>>>
>>>
>>
>
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