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

[Thomas Jablin]

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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