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

[Thomas Jablin]

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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