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

[Thomas Jablin]

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
>> >
>> >
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>>
>
>
>
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