[lld] r229762 - PECOFF: Fix symbol aliases

[Rui Ueyama]

On Wed, Feb 18, 2015 at 6:44 PM, Shankar Easwaran <shankare at codeaurora.org>
wrote:

>  Hi Rui,
>
> This is only in the Context of modeling Alias symbols. I agree we dont
> want to bring the complete LayoutPass for simple usecases.
>
> Do you have a different solution/design that works with ordinals to layout
> multiple alias atoms ?
>

It's too simple so I don't know if we can call it a solution or a design,
but we can define 2^32 aliases for an atom in this way.

Are you considering / need to support more than one alias to the *first *atom
> created for a file ?
>

That should work already. As I described in the comment for getNextOrdinal,
the ordinal of the first real atom is 1<<32 (not 0), so we can assign any
number between 0 to 1<<32-1 to aliases for the first atom.


>
> Shankar Easwaran
>
>
> On 2/18/2015 8:28 PM, Rui Ueyama wrote:
>
> I know you wanted to bring LayoutPass back, and I think I described about
> why that's not a good idea many times. The most recent discussion is this.
> Could you read this and then elaborate why you think we should use the
> LayoutPass based on that discussion?
> http://lists.cs.uiuc.edu/pipermail/llvmdev/2015-February/082130.html
>
> On Wed, Feb 18, 2015 at 6:06 PM, Shankar Easwaran <shankare at codeaurora.org> <shankare at codeaurora.org>
> wrote:
>
>
>  I feel using kindLayoutBefore references would be a preferred way for this
> solution.
>
> We could enable the LayoutPass only if Alias symbols exist. Does COFF need
> alias symbols for default operation ?
>
> Shankar Easwaran
>
>
> On 2/18/2015 5:50 PM, Rui Ueyama wrote:
>
>
>  On Wed, Feb 18, 2015 at 3:47 PM, Shankar Easwaran <shankare at codeaurora.org>
> wrote:
>
>  On 2/18/2015 5:11 PM, Rui Ueyama wrote:
>
>   +  alias->setOrdinal(target->ordinal() - 1);
>
>   Wouldn't this cause a wrap around when the ordinal of the first atom
>
>  is 0 ?
>
>     +// getNextOrdinal returns a monotonically increasaing uint64_t
>
>  number
> +// starting from 1. There's a large gap between two numbers returned
> +// from this function, so that you can put other atoms between them.
> +uint64_t FileCOFF::getNextOrdinal() {
> +  return _ordinal++ << 32;
> +}
> +
>
>  Do you need it this to be shifted by 32 ? Wouldnt incrementing by 2 be
>
>  enough ?
>
>
>  You could define two or more aliases to a symbol so we need more room than
> for one alias. That doesn't work now, though.
>
>
>
>
>  Shankar Easwaran
>
> --
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted
> by the Linux Foundation
>
>
>
>
>  --
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted
> by the Linux Foundation
>
>
>
>
>
> --
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by the Linux Foundation
>
>
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