code review 4639077: ld: fix ELF strip by removing overlap of sections

ld: fix ELF strip by removing overlap of sections

The gosymtab and gopclntab sections were pointing to the proper
data, but that data was already owned by the rodata section.
Some ELF references explicitly prohibit multiple sections from
owning the same data, and strip behaves accordingly.

The data for these sections was moved to after rodata, and the
gosymtab and gopclntab sections now own their respective ranges.

This change makes strip happy both with and without -s being
provided at link time.  Note that it won't remove these sections
because they are still allocated, and that's by design since
they are necessary at runtime for generating proper backtraces
and similar introspection operations.

Unlike the previous behavior, -s will now maintain zero-sized
gosymtab and gopclntab sections.  This makes the implementation
slightly cleaner.

Fixes issue 1242.

NOTE: Tested on Linux amd64/386/arm only.

[niemeyer, 2011-06-28 00:15:51]

Hello golang-dev@googlegroups.com,

I'd like you to review this change to
https://go.googlecode.com/hg/

[ality, 2011-06-28 01:31:46]

n13m3y3r@gmail.com once said:
> Unlike the previous behavior, -s will now maintain zero-sized
> gosymtab and gopclntab sections.  This makes the implementation
> slightly cleaner.

That means elfshbits will set them to NOBITS, right?
Does the spec allow a NOBITS section to be inside a
segment set to LOAD?

Otherwise, LGTM.

  Anthony

P.S.
I also made sure there was no regression on Plan 9. :)

http://codereview.appspot.com/4639077/

[rsc, 2011-06-28 02:35:37]

LGTM

In CL description, s/Fixes/Fixes issue/

[niemeyer, 2011-06-28 21:28:35]

*** Submitted as http://code.google.com/p/go/source/detail?r=2efa68a4183d ***

ld: fix ELF strip by removing overlap of sections

The gosymtab and gopclntab sections were pointing to the proper
data, but that data was already owned by the rodata section.
Some ELF references explicitly prohibit multiple sections from
owning the same data, and strip behaves accordingly.

The data for these sections was moved to after rodata, and the
gosymtab and gopclntab sections now own their respective ranges.

This change makes strip happy both with and without -s being
provided at link time.  Note that it won't remove these sections
because they are still allocated, and that's by design since
they are necessary at runtime for generating proper backtraces
and similar introspection operations.

Unlike the previous behavior, -s will now maintain zero-sized
gosymtab and gopclntab sections.  This makes the implementation
slightly cleaner.

Fixes issue 1242.

NOTE: Tested on Linux amd64/386/arm only.

R=ality, rsc
CC=golang-dev
http://codereview.appspot.com/4639077

[niemeyer, 2011-06-28 21:29:44]

> Does the spec allow a NOBITS section to be inside a
> segment set to LOAD?

Note .bss is also NOBITS.

> I also made sure there was no regression on Plan 9. :)

Thanks!

[zhai, 2011-06-29 02:21:32]

There are still some overlapped sections in binary file "goinstall" and
"godoc"

GOARCH=386
godoc:
.rodata 8177000-825c96b  overlaps .dynsym 81772cc-81773eb
.rodata 8177000-825c96b  overlaps .dynstr 81773ec-8177517
.rodata 8177000-825c96b  overlaps .gnu.version 8177008-817702b
.rodata 8177000-825c96b  overlaps .gnu.version_r 817702c-817708b
.rodata 8177000-825c96b  overlaps .rel.plt 81770f4-817715b
.rodata 8177000-825c96b  overlaps .plt 81771ec-81772cb
.rodata 8177000-825c96b  overlaps .hash 817708c-81770f3
.rodata 8177000-825c96b  overlaps .rel 8177000-8177007
.data 8340000-83428d7  overlaps .got.plt 83401c0-83401ff

goinstall:
.rodata 813d000-81fe3af  overlaps .dynsym 813d2cc-813d3eb
.rodata 813d000-81fe3af  overlaps .dynstr 813d3ec-813d517
.rodata 813d000-81fe3af  overlaps .gnu.version 813d008-813d02b
.rodata 813d000-81fe3af  overlaps .gnu.version_r 813d02c-813d08b
.rodata 813d000-81fe3af  overlaps .rel.plt 813d0f4-813d15b
.rodata 813d000-81fe3af  overlaps .plt 813d1ec-813d2cb
.rodata 813d000-81fe3af  overlaps .hash 813d08c-813d0f3
.rodata 813d000-81fe3af  overlaps .dynamic 813d15c-813d1eb
.data 82bb000-82bd847  overlaps .got.plt 82bb260-82bb29f


On Wed, Jun 29, 2011 at 5:29 AM, <n13m3y3r@gmail.com> wrote:

> Does the spec allow a NOBITS section to be inside a
>> segment set to LOAD?
>>
>
> Note .bss is also NOBITS.
>
>
>  I also made sure there was no regression on Plan 9. :)
>>
>
> Thanks!
>
>
http://codereview.appspot.com/**4639077/<http://codereview.appspot.com/4639077/>
>

[gustavo_niemeyer.net, 2011-06-29 08:20:27]

> There are still some overlapped sections in binary file "goinstall" and
> "godoc"

Can you please open another bug about this?  A similar fix has to be
applied to dynamic binaries.

I'll work on that next.

-- 
Gustavo Niemeyer
http://niemeyer.net
http://niemeyer.net/blog
http://niemeyer.net/twitter

[zhai, 2011-06-29 08:59:18]

Done,
new issue 2022
http://code.google.com/p/go/issues/detail?id=2022&colspec=ID%20Status%20Stars...

On Wed, Jun 29, 2011 at 4:20 PM, Gustavo Niemeyer <gustavo@niemeyer.net>wrote:

> > There are still some overlapped sections in binary file "goinstall" and
> > "godoc"
>
> Can you please open another bug about this?  A similar fix has to be
> applied to dynamic binaries.
>
> I'll work on that next.
>
> --
> Gustavo Niemeyer
> http://niemeyer.net
> http://niemeyer.net/blog
> http://niemeyer.net/twitter
>