Re: Read .debug_line without .debug_info

[Mark Wielaard <mark@klomp.org>]

On Mon, 2018-03-26 at 21:24 +0200, Torsten Polle wrote:
> > > > Am 26.03.2018 um 21:12 schrieb Mark Wielaard <mark@klomp.org>:
> > On Mon, Mar 26, 2018 at 04:41:06PM +0000, Sasha Da Rocha Pinheiro wrote:
> > > is it possible to read contents of .debug_line section without the
> > > presence of a .debug_info section?
> > 
> > No, because .debug_line sections need some information from the CU
> > which comes from the .debug_info. In particular the directory table
> > starts with the compilation directory which can only be gotten from
> > the CU (DW_AT_comp_dir). The files in the file list (which don't have
> > an explicit dir associated) are all given relative to that comp dir.
> 
> you could take this information from the include directories:
> 
> "11. include_directories (sequence of path names)
> 
> Entries in this sequence describe each path that was searched for included source files in this compilation. (The paths include those directories specified explicitly by the user for the compiler to search and those the compiler searches without explicit direction.) Each path entry is either a full path name or is relative to the current directory of the compilation.
> 
> The last entry is followed by a single null byte.
> 
> The line number program assigns numbers to each of the file entries in order, beginning with 1. The current directory of the compilation is understood to be the zeroth entry and is not explicitly represented."

Yes, you are right, if the files don't refer to the current directory
(index zero). But normally most files will be relative to the current
directory, which (at least in DWARF < 5) is not explicitly represented
in the directory table, only implicitly as the CU comp_dir attribute.

Also if you are interested in the code ranges that are covered by the
line table, you have to parse the whole table up front without an
associated debuginfo CU DIE. This might or might not be an issue, but
it is if you have multiple line tables and you quickly need to find the
one that covers a specific address.

So, yes, the line tables might be usable without the .debug_info
present, but it isn't as convenient.

Cheers,

Mark