https://sourceware.org/bugzilla/show_bug.cgi?id=23310
Bug ID: 23310
Summary: Support DWARF-5 line table features in assembler
Product: binutils
Version: unspecified
Status: UNCONFIRMED
Severity: normal
Priority: P2
Component: gas
Assignee: unassigned at sourceware dot org
Reporter: paul_robinson at playstation dot sony.com
Target Milestone: ---
DWARF-5 has two line-table features that are probably best handled by
extensions to the .file directive in the assembler.
(a) provide an MD5 checksum of the source file, as a more reliable way
to verify whether the source file has changed since compilation.
(b) explicitly provide the root source file as "file #0" in the file
table, making the line table fully independent of the .debug_info
section.
The existing .file directive syntax is:
.file filenumber [ "directory" ] "path"
To support MD5 checksums computed by the compiler, I propose making
the syntax be
.file filenumber [ "directory" ] "path" [ md5 checksum ]
where 'md5' is a keyword and checksum is the 128-bit integer checksum,
which can be expressed in the same ways that the .octa directive allows.
If all .file directives provide an MD5 checksum, then the line-table
header will include the provided values using DW_LNCT_MD5.
If not all .file directives provide the MD5 clause, then DW_LNCT_MD5
should be omitted (as DWARF does not provide a way to give MD5 values
for some files but not others in the same compilation unit).
To support the root file, I propose that the filenumber is allowed to
have the value 0 (currently must be >= 1). If no ".file 0" appears,
then replicate the file #1 entry as file #0. This permits the same
assembler source to be used to generate either DWARF-4 or DWARF-5
without complaint.
I have implemented these features in the LLVM assembler.
In response to a question on the binutils list, no I am not offering
to implement the features in the GNU assembler. But it seems like a
good idea for both assemblers to support the same syntax.
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