Re: pdumping "into" the executable

[dancol]

> On 02/26/2018 02:22 PM, Daniel Colascione wrote:
>> On 12/31/1969 04:00 PM, Paul Eggert wrote:
>>> On 02/26/2018 01:18 PM, address@hidden wrote:
>>>>> Or, just turn the dump to a C file, then compile it
>>>>> and do a second link.  Aside from (maybe hypothetical) C compiler
>>>>> limits, that would be very portable.
>>>> But not redumpable.
>>>
>>> Why couldn't it be redumpable? All that the user should need is a C
>>> compiler. That's not unreasonable.
>>
>> I thought we had this argument back when we were talking about
>> modules. I think it's unacceptable to require a C compiler and the
>> presence of Emacs unlinked objects for the proper operation of an
>> end-user feature.
>
> Although using a dumped Emacs is an end-user feature, dumping and
> redumping are not. Dumping and/or redumping are techniques used to build
> Emacs, and in practice they should be part of a software build system;
> for such a thing it's reasonable to assume a C compiler.
>
> We already assume a C compiler (or equivalent) when building modules; we
> don't assume a C compiler only when people are using the modules.
> Dumping is similar.
>
>>
>>>> Besides, the problem with a second link is that it might change the
>>>> relative positions of symbols within Emac
>>>
>>> How could that be a problem? Symbols known to C code are known by
>>> their fixed offsets and the second link wouldn't change these
>>> offsets, and symbols not known to C code need to be reallocated
>>> anyway during loading.
>>
>> The linker is what determines into-translation-unit offsets, not the
>> compiler. The offsets are patched in at link time. There's no
>> particular requirement to perform the link the same way every time.
>
> For Lisp symbols visible to C, Emacs master currently determines symbol
> offsets at C-compile-time, not at link time. Does pdumper change this?
> If so, how and why does it change this? And if not, then I don't see the
> problem.

The built-in symbols are in one big contiguous array. That's why the
scheme works.