[gclist] Boehm GC & Linux/SPARC

[Boehm, Hans]

> Q2: Is anyone using the Boehm et al collector with Linux/SPARC?
> There seems to be some code in it to handle that combination, but it
> doesn't work.  I tried it (using cf.sourceforge.net) and found that it
> crashes very early.  The definition of DATASTART using 
> LINUX_DATA_START
> doesn't work, because __data_start is not defined (both __data_start
> and data_start are zero).
> 
> I had a look at the linker script (output by `ld -v'),
> and based on that, I tried using __etext for DATASTART.
> However, that didn't work, because there are some unmapped pages
> between the rodata (which follows __etext) and the other data.
> There didn't seem to be any linker-defined symbol I could use
> to find the end of rodata or the start of the remaining data.
> 
This seems to be somewhat distribution dependent.  (Dependent on both glibc
and the linker script, to be more precise.)  I believe there is now a
consensus that __data_start should be defined, and it is defined in glibc on
most of the architectures, I believe.  If it still isn't defined on SPARC,
there's a good chance the glibc maintainer (drepper@redhat.com) would
appreciate a patch.

In the latest 6.0alpha versions, if you define SEARCH_FOR_DATA_START the
collector will look for a nonzero definition of first __data_start, then
data_start, and then search backward from _end if they both fail.  That
should work OK if someone also submits the glibc patch.

My version actually uses GC_SysVGetDataStart on Linux/SPARC.  Does that not
work?

Hans