code review 223068: Add -r option to 6l/8l/5l.

Add -r option to 6l/8l/5l.

This permits more flexibility with cgo and swig in cases where
the program is run on a machine other than the one on which it
is built.  Rather than storing the absolute path to the shared
library in the DT_NEEDED entry, we can store just the name,
and let the dynamic linker find it using DT_RUNPATH or the
LD_LIBRARY_PATH environment variable.

[iant, 2010-02-26 21:06:10]

Hello rsc (cc: golang-dev@googlegroups.com),

I'd like you to review this change.

[rsc, 2010-02-26 21:08:16]

LGTM

Is there a way to use hierarchical paths with -r?
I hard-code whole path names in cgo because
I couldn't figure out how to do a relative lookup
for container/vector.so (say).

[r2, 2010-02-26 21:14:50]

please add the flag to doc.go in those directories.

On 27/02/2010, at 8:06 AM, iant@golang.org wrote:

> Reviewers: rsc,
> 
> Message:
> Hello rsc (cc: golang-dev@googlegroups.com),
> 
> I'd like you to review this change.
> 
> 
> Description:
> Add -r option to 6l/8l/5l.
> 
> This permits more flexibility with cgo and swig in cases where
> the program is run on a machine other than the one on which it
> is built.  Rather than storing the absolute path to the shared
> library in the DT_NEEDED entry, we can store just the name,
> and let the dynamic linker find it using DT_RUNPATH or the
> LD_LIBRARY_PATH environment variable.
> 
> Please review this at http://codereview.appspot.com/223068/show
> 
> Affected files:
>  M src/cmd/5l/asm.c
>  M src/cmd/5l/l.h
>  M src/cmd/5l/obj.c
>  M src/cmd/6l/asm.c
>  M src/cmd/6l/l.h
>  M src/cmd/6l/obj.c
>  M src/cmd/8l/asm.c
>  M src/cmd/8l/l.h
>  M src/cmd/8l/obj.c
> 
> 

[iant2, 2010-02-26 21:19:13]

Russ Cox <rsc@golang.org> writes:

> Is there a way to use hierarchical paths with -r?
> I hard-code whole path names in cgo because
> I couldn't figure out how to do a relative lookup
> for container/vector.so (say).

When a DT_NEEDED entry contains a '/', the dynamic linker ignores
DT_RUNPATH and LD_LIBRARY_PATH when searching for that entry.  You can
still use $ORIGIN, which expands to the directory holding the binary
being run, but you can't do any other path searching.

-r does permit a sequence of paths separated by colons, so I suppose
in principle you could figure out all the subdirectories you need and
list them.

Ian

[iant2, 2010-02-26 21:25:27]

"Rob 'Commander' Pike" <r@google.com> writes:

> please add the flag to doc.go in those directories.

Added to CL.

Ian

[r2, 2010-02-26 21:32:48]

docs LGTM

[rsc, 2010-02-26 21:35:18]

Sounds like maybe a better option is to
use -r $GOROOT/pkg/$GOOS_$GOARCH
and then use an escaped form of the object
name to flatten the slashes.

Good to know, thanks.

Russ

[iant, 2010-02-26 22:04:03]

*** Submitted as http://code.google.com/p/go/source/detail?r=7dfb7f11a440 ***

Add -r option to 6l/8l/5l.

This permits more flexibility with cgo and swig in cases where
the program is run on a machine other than the one on which it
is built.  Rather than storing the absolute path to the shared
library in the DT_NEEDED entry, we can store just the name,
and let the dynamic linker find it using DT_RUNPATH or the
LD_LIBRARY_PATH environment variable.

R=rsc
CC=golang-dev
http://codereview.appspot.com/223068