From: Fangrui Song <maskray@google.com>
To: Alan Modra <amodra@gmail.com>
Cc: David Blaikie <dblaikie@gmail.com>,
Mark Wielaard <mark@klomp.org>,
gdb@sourceware.org, elfutils-devel@sourceware.org,
binutils@sourceware.org
Subject: Re: Range lists, zero-length functions, linker gc
Date: Tue, 2 Jun 2020 21:06:29 -0700 [thread overview]
Message-ID: <20200603040629.qib2patdxob5o5lw@google.com> (raw)
In-Reply-To: <20200603031040.GD29024@bubble.grove.modra.org>
On 2020-06-03, Alan Modra 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.
>
>--
>Alan Modra
>Australia Development Lab, IBM
sizeof(Elf64_Shdr) = 64.
If we create a .debug_line fragment and a .debug_info fragment for a
function, we waste 128 bytes.
https://sourceware.org/pipermail/binutils/2020-May/111361.html
> .debug_line.bar
We should use the unique linkage feature https://sourceware.org/bugzilla/show_bug.cgi?id=25380
otherwise we also waste lots of bytes for the .debug_*.* section names.
next prev parent reply other threads:[~2020-06-03 4:06 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 [this message]
2020-06-03 21:50 ` David Blaikie
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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