[TUHS] v6tar from v7 on v6, too large?

Noel Chiappa jnc at mercury.lcs.mit.edu
Thu Dec 10 08:01:26 AEST 2015

    > Yes the V6 kernel runs in split I and D mode, but it doesn't end up
    > supporting any more data.  I.e. the kernel is still a 407 (or 410) file.
    > _etext/_edata/_end are still referencing the same 64K space.

Err, actually, not really.

The thing is that to build the split-I/D kernel, one sets the linker to
produce an output file which still contains the relocation bits. That is then
post-processed by 'sysfix', which does wierd magic (moves the text up to
020000, in terms of address space; and puts the data _below_ the text, in the
actual output file). So while the files concerned may have a '407' in their
header, they definitely aren't what one normally finds in a linked 407 or 410

In particular, data addresses start at 0, and can run up to 0140000 (i.e. up
to 56KB), while text addreses start at 020000 and can run up to 0160000. So,
_etext/_edata/_end are not, in fact, in the same 64K space. And the total of
data (initialized and un-initialized) together with the text can be much
larger than 64KB - up to 112KB (modor so.


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