On 7/16/20 11:51 AM, David Blaikie wrote:
On Thu, Jul 16, 2020 at 11:41 AM Robinson, Paul via Dwarf-Discuss
The example that most often comes up is Harvard architectures. As it
happens, I think it's nearly always obvious from context whether a given
address is data-segment or code-segment. The only time it's not,
that I'm
aware of, is in the .debug_aranges section, where addresses are
associated
with compile-units without any indication of whether they are code
or data
addresses. I've heard arguments that .debug_aranges should only
have code
addresses in it, but I don't think that's what the spec says.
Curious - the spec doesn't seem to read that way to me - and if that
were its goal, it seems like DW_AT_segment wouldn't really be needed.
As Paul said, DW_AT_segment is not generally needed to describe a
Harvard architecture.
DW_AT_locations would always be data, DW_AT_high/low/ranges would always
be code, etc? The spec... specifically says DW_AT_segment applies to
high/low/ranges, and describes a parent-DIE delegation scheme that seems
to suggest that some DIEs could have one segment, and others could have
a different segment - but no way for ranges to have different segments
in different parts of the same range list, which seems to be at odds
with the ability to vary segment across a DIE tree - you couldn't put a
ranges at the top of such a variegated tree...
On some (many?) architectures, data and code may be interspersed, for
example, to place constant data with the executable text.
DIEs can have different DW_AT_segments.
Entries in .debug_aranges have segment, offset, and length.
What is the use case for having multiple segments in a range list?
(& yeah, the arange situation crossed my mind too - on both counts you
noted (that it needs it, but that it may not - because some
interpretations suggest it should only contain code addresses anyway))
As Paul mentioned, that's not what the spec says.
& not sure how any of this resolves the "but debug_addr has segment
selectors"
nor "what's the point of segment selector size in debug_rnglists,
debug_loclists, and debug_line" - none of those sections seem to contain
segment selectors, so why do their headers describe the size of such a
thing?
Location lists contain segment, offset, and length.
--
Michael Eager
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