code review 65740045: cmd/ld: remove Plan 9 symbol table

cmd/ld: remove Plan 9 symbol table

Update issue 6853

Nothing reads the Plan 9 symbol table anymore.
The last holdout was 'go tool nm', but since being rewritten in Go
it uses the standard symbol table for the binary format
(ELF, Mach-O, PE) instead.

Removing the Plan 9 symbol table saves ~15% disk space
on most binaries.

Two supporting changes included in this CL:

debug/gosym: use Go 1.2 pclntab to synthesize func-only
symbol table when there is no Plan 9 symbol table

debug/elf, debug/macho, debug/pe: ignore final EOF from ReadAt

[rsc, 2014-02-19 03:48:08]

Hello r (cc: golang-codereviews@googlegroups.com),

I'd like you to review this change to
https://code.google.com/p/go/

[r, 2014-02-19 03:51:14]

LGTM
yay

update issue 6853

[bradfitz, 2014-02-19 03:57:04]

Yay indeed.




On Tue, Feb 18, 2014 at 7:48 PM, <rsc@golang.org> wrote:

> Reviewers: r,
>
> Message:
> Hello r (cc: golang-codereviews@googlegroups.com),
>
> I'd like you to review this change to
> https://code.google.com/p/go/
>
>
> Description:
> cmd/ld: remove Plan 9 symbol table
>
> Nothing reads the Plan 9 symbol table anymore.
> The last holdout was 'go tool nm', but since being rewritten in Go
> it uses the standard symbol table for the binary format
> (ELF, Mach-O, PE) instead.
>
> Saves ~15% disk space on most binaries.
>
> Two supporting changes included in this CL:
>
> debug/gosym: use Go 1.2 pclntab to synthesize func-only
> symbol table when there is no Plan 9 symbol table
>
> debug/elf, debug/macho, debug/pe: ignore final EOF from ReadAt
>
> Please review this at https://codereview.appspot.com/65740045/
>
> Affected files (+46, -170 lines):
>   M src/cmd/ld/symtab.c
>   M src/pkg/debug/elf/file.go
>   M src/pkg/debug/gosym/pclntab.go
>   M src/pkg/debug/gosym/symtab.go
>   M src/pkg/debug/macho/file.go
>   M src/pkg/debug/pe/file.go
>
>
> --
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>

[rsc, 2014-02-19 04:38:00]

FWIW, also saves 9 seconds on all.bash (5%).

Russ

[r, 2014-02-19 04:39:50]

That's not nothing.

[rsc, 2014-02-19 04:41:19]

*** Submitted as https://code.google.com/p/go/source/detail?r=737767dd81fd ***

cmd/ld: remove Plan 9 symbol table

Update issue 6853

Nothing reads the Plan 9 symbol table anymore.
The last holdout was 'go tool nm', but since being rewritten in Go
it uses the standard symbol table for the binary format
(ELF, Mach-O, PE) instead.

Removing the Plan 9 symbol table saves ~15% disk space
on most binaries.

Two supporting changes included in this CL:

debug/gosym: use Go 1.2 pclntab to synthesize func-only
symbol table when there is no Plan 9 symbol table

debug/elf, debug/macho, debug/pe: ignore final EOF from ReadAt

LGTM=r
R=r, bradfitz
CC=golang-codereviews
https://codereview.appspot.com/65740045

[dfc, 2014-02-19 04:41:57]

The arm builders count time in dog years, that is more than a minute in their
timeframe. 

> On 19 Feb 2014, at 15:39, Rob Pike <r@golang.org> wrote:
> 
> That's not nothing.
> 
> -- 
> You received this message because you are subscribed to the Google Groups
"golang-codereviews" group.
> To unsubscribe from this group and stop receiving emails from it, send an
email to golang-codereviews+unsubscribe@googlegroups.com.
> For more options, visit https://groups.google.com/groups/opt_out.

[minux1, 2014-02-19 04:42:14]

Both the time and space save are great! Thank you.

[bradfitz, 2014-02-19 04:50:25]

I see a 25% reduction:

Before:
-rwxr-xr-x  1 bradfitz  staff  23556028 Feb 18 20:47 bin/camlistored
After:
-rwxr-xr-x  1 bradfitz  staff  17727420 Feb 18 20:48 bin/camlistored




On Tue, Feb 18, 2014 at 8:41 PM, <rsc@golang.org> wrote:

> *** Submitted as
> https://code.google.com/p/go/source/detail?r=737767dd81fd ***
>
>
> cmd/ld: remove Plan 9 symbol table
>
> Update issue 6853
>
>
> Nothing reads the Plan 9 symbol table anymore.
> The last holdout was 'go tool nm', but since being rewritten in Go
> it uses the standard symbol table for the binary format
> (ELF, Mach-O, PE) instead.
>
> Removing the Plan 9 symbol table saves ~15% disk space
>
> on most binaries.
>
> Two supporting changes included in this CL:
>
> debug/gosym: use Go 1.2 pclntab to synthesize func-only
> symbol table when there is no Plan 9 symbol table
>
> debug/elf, debug/macho, debug/pe: ignore final EOF from ReadAt
>
> LGTM=r
> R=r, bradfitz
> CC=golang-codereviews
> https://codereview.appspot.com/65740045
>
>
> https://codereview.appspot.com/65740045/
>

[aram, 2014-02-19 05:05:38]

Will this break acid symbols in Plan 9?

[rsc, 2014-02-19 05:13:37]

On Wed, Feb 19, 2014 at 12:05 AM, <aram@mgk.ro> wrote:

> Will this break acid symbols in Plan 9?
>

No. Before this CL the Go binaries on Plan 9 actually contained two Plan 9
symbol tables. (That's not entirely fair; the one used by Go is an
evolution of the original form, so it is unintelligible to Plan 9 and vice
versa.)

Russ

[aram, 2014-02-19 05:15:02]

Thank you.