From: David Blaikie <dblaikie@gmail.com>
To: Alan Modra <amodra@gmail.com>
Cc: Mark Wielaard <mark@klomp.org>,
gdb@sourceware.org, elfutils-devel@sourceware.org,
binutils@sourceware.org, Fangrui Song <maskray@google.com>
Subject: Re: Range lists, zero-length functions, linker gc
Date: Wed, 3 Jun 2020 14:50:49 -0700 [thread overview]
Message-ID: <CAENS6EvzJh6Z_XaqOWg+f0k0grXzBVSruHNvJSy=fNaakOtxcQ@mail.gmail.com> (raw)
In-Reply-To: <20200603031040.GD29024@bubble.grove.modra.org>
On Tue, Jun 2, 2020 at 8:10 PM Alan Modra <amodra@gmail.com> wrote:
>
> On Tue, Jun 02, 2020 at 11:06:10AM -0700, David Blaikie via Binutils wrote:
> > On Tue, Jun 2, 2020 at 9:50 AM Mark Wielaard <mark@klomp.org> wrote:
> > > where I
> > > would argue the compiler simply needs to make sure that if it generates
> > > code in separate sections it also should create the DWARF separate
> > > section (groups).
> >
> > I don't think that's practical - the overhead, I believe, is too high.
> > Headers for each section contribution (ELF headers but DWARF headers
> > moreso - having a separate .debug_addr, .debug_line, etc section for
> > each function would be very expensive) would make for very large
> > object files.
>
> With a little linker magic I don't see the neccesity of duplicating
> the DWARF headers. Taking .debug_line as an example, a compiler could
> emit the header, opcode, directory and file tables to a .debug_line
> section with line statements for function foo emitted to
> .debug_line.foo and for bar to .debug_line.bar, trusting that the
> linker will combine these sections in order to create an output
> .debug_line section. If foo code is excluded then .debug_line.foo
> info will also be dropped if section groups are used.
I don't think this would apply to debug_addr - where the entries are
referenced from elsewhere via index, or debug_rnglist where the
rnglist header (or the debug_info directly) contains offsets into this
section, so taking chunks out would break those offsets. (or to the
file/directory name part of debug_line - where you might want to
remove file/line entries that were eliminated as dead code - but
that'd throw off the indexes)
next prev parent reply other threads:[~2020-06-03 21:51 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-31 18:55 Fangrui Song
2020-05-31 19:15 ` Fangrui Song
2020-05-31 20:10 ` Mark Wielaard
2020-05-31 20:47 ` Fangrui Song
2020-05-31 22:11 ` Mark Wielaard
2020-05-31 23:17 ` David Blaikie
2020-05-31 20:49 ` David Blaikie
2020-05-31 22:29 ` Mark Wielaard
2020-05-31 22:36 ` David Blaikie
2020-06-01 9:31 ` Mark Wielaard
2020-06-01 20:18 ` David Blaikie
2020-06-02 16:50 ` Mark Wielaard
2020-06-02 18:06 ` David Blaikie
2020-06-03 3:10 ` Alan Modra
2020-06-03 4:06 ` Fangrui Song
2020-06-03 21:50 ` David Blaikie [this message]
2020-06-09 20:24 ` Tombstone values in debug sections (was: Range lists, zero-length functions, linker gc) Fangrui Song
2020-06-19 20:04 ` Mark Wielaard
2020-06-20 1:02 ` David Blaikie
2020-06-19 12:00 ` Range lists, zero-length functions, linker gc Mark Wielaard
2020-06-20 0:46 ` David Blaikie
2020-06-24 22:21 ` Mark Wielaard
2020-06-25 23:45 ` David Blaikie
2020-05-31 21:33 ` David Blaikie
2020-06-01 16:25 ` Andrew Burgess
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