On 6/26/22 05:52, Vsevolod Alekseyev via Dwarf-Discuss wrote:
Greetings,
I’m involved with a Python DWARF parser, Pyelftools (
https://github.com/eliben/pyelftools/
<https://github.com/eliben/pyelftools/> ). I have a question about
DWARF5 and the newly indexed loclists/rnglists sections, please.
In those sections, each CU gets a block. The block starts with a header,
which starts with a 4/12 byte unit_length field, which also serves as a
bitness indicator (32/64) – right? So the size of the offset values in
the offset table below the header is driven by the structure of
unit_length. The DWARF5 standard, section 7.29 talks about “32-bit
DWARF” and “64-bit DWARF” without making clear which of the bitness
indicators should be used – the one from the original DIE’s CU, or the
one from the CU header loclists where the DIE points. I was presuming
all along that it’s latter; can someone please confirm? Thank you.
The 32/64 indicator is what the standard calls lengths and offset
sizes. DWARF5 Section 7.4.
The intent was always that all content related to a single CU (whether
in one section or more than one, as in your question) have the SAME
offset size. Meaning either place one looks at the 32/64 offset size
related to a CU it must match the CU header offset size.
Unfortunately DWARF3-DWARF5 do not clearly say this.
I'm likely not saying it clearly...sigh.
(DWARF2 did not allow for a 64bit offset/length size).
If the offset sizes related to a single CU in sections
like loclists/rngslists do not match the CU offset size the DWARF is
corrupt.
An elf file could have one CU with 32 and another CU with 64 bit offset
size mixed into a single object file. Each with its associated
loclists/rnglists (etc) with the offset size of its CU.
This possibility too was always intended (starting with DWARF3).
Corrections/clarifications are welcome.
Hope this makes sense.
David Anderson
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