Re: rtl metadata musings

[Andy Wingo]

On Mon 20 May 2013 18:37, address@hidden (Ludovic Courtès) writes:

> Andy Wingo <address@hidden> skribis:
>
>> On Sun 19 May 2013 23:52, address@hidden (Ludovic Courtès) writes:
>>
>>> I guess literal strings would go out as per ‘SCM_IMMUTABLE_STRING’
>>> (which needs relocation), right?
>>
>> Yep.  Right now the stringbuf goes into read-only memory, but the string
>> itself goes in writable memory as it needs its link to the stringbuf
>> fixed up (relocated) at runtime.
>
> OK.  It could be in a PT_GNU_RELRO segment, which the loader (well, the
> other one, from glibc ;-)) remaps read-only after relocation.
>
> [A moment of enlightenment when one realizes what it means to have our
> own ELF toolchain.  :-)]

Right :) We don't need to rely on the loader, and in fact should not in
general do so.  Some "relocations" are actually more complicated than
what glibc does; for example, for symbols or keywords.

>> (I suppose we should be careful about embedded NUL characters; perhaps
>> we should use some other format for the string tables.)
>
> NULs in string contents should not be a problem, as long as there’s
> info somewhere about the string length, no?

There isn't -- not in ELF string tables.  They're NUL-terminated.

> UTF-8-encoded ELF symbols may be more of a problem.  How could NULs in
> symbols be handled?

Well we can just use some other data structure that's not a standard ELF
string table; since we have the linker and loader and we are defining
custom sections (.guile.docstrs for example) we can do what we like.

A
-- 
http://wingolog.org/