Add a warning for unknown cross-mapping references

Some segments, like the 'vectors' one, will reference code that is
outside of its mapping. But in some other configurations, segments
cannot make these cross-mapping references so happily. Imagine:

    .segment "SWAPPABLE"

    .proc foo
        rts
    .endproc

    .segment "FIXED"

    jsr foo

Here the assembler will properly detect the address of 'foo' in the
context of the 'SWAPPABLE' segment. But what this assembler doesn't know
is that this segment is swappable (e.g. UNROM chip). Hence, if the bank
being mapped right now is not the one containing the 'SWAPPABLE'
segment, then the address computed for 'foo' and used in that 'jsr'
instruction will point to something else entirely. This would be similar
to a use-after-free bug.

This is something that can only be inspected at runtime, and so the
assembler cannot be of much help here. Hence, this commit adds a warning
so the programmer can understand the potentially dangerous operation.

All of that being said, this commit also adds support for "asan:safe" or
"check:safe", which is a magic comment that the programmer can write to
re-assure the assembler that this operation is fine (e.g. there is a
guarantee that the mapped bank is that one we are expecting). Hence, the
code above could now be written like so:

    jsr foo      ; check:safe

Signed-off-by: Miquel Sabaté Solà <mssola@mssola.com>

0 files changed, 0 insertions, 0 deletions