ld: set --enable-new-dtags by default

[bukzor]

The --enable-new-dtags option to ld causes it to emit a RUNPATH rather than RPATH entry in the elf header. Because the Android linker supports RUNPATH but not RPATH, this means many things can now Just Work. This should (eventually) eliminate the need to set LD_LIBRARY_PATH.

Prior art:

This became the default for Linux in 2013 but I think termux isn't getting it because it reports "Android" instead of "Linux"? Or maybe the way it works changed since then. Regardless, Debian has been using RUNPATH by default since December 2016. Their newest configuration uses the newer configuration option seen in this patch. The suse and gentoo maintainers said they did the same in 2004 and 2005, respectively. So it seems well battle-tested, to me.

For the curious:
This came up because I'm working on getting Homebrew working under Termux.

[fornwall]

Thanks - the updated package is now available at version 2.30-1 as an update!

This came up because I'm working on getting Homebrew working under Termux.

Interesting! Let us know how it goes (I guess #2071 is the best location to post progress)!

[sjackman]

RPATH is the default on Ubuntu 16.04 (Xenial Xerus).

❯❯❯ echo 'int main() { return 0; }' >hello.c
❯❯❯ gcc -Wl,-rpath=/foo -o hello hello.c
❯❯❯ readelf -d hello | egrep 'RPATH|RUNPATH'
 0x000000000000000f (RPATH)              Library rpath: [/foo]
❯❯❯ gcc -Wl,-rpath=/foo -Wl,--enable-new-dtags -o hello hello.c
❯❯❯ readelf -d hello | egrep 'RPATH|RUNPATH'
 0x000000000000001d (RUNPATH)            Library runpath: [/foo]

[bukzor]

I believe the change happened in binutils 2.27. For comparison:

$ echo 'int main() { return 0; }' >hello.c
$ gcc -Wl,-rpath=/foo -o hello hello.c
$ readelf -d hello | egrep 'RPATH|RUNPATH'
 0x000000000000001d (RUNPATH)            Library runpath: [/foo]

$ gcc -Wl,-rpath=/foo -Wl,--enable-new-dtags -o hello hello.c
$ readelf -d hello | egrep 'RPATH|RUNPATH'
 0x000000000000001d (RUNPATH)            Library runpath: [/foo]

$ dpkg -l binutils
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
||/ Name           Version      Architecture Description
+++-==============-============-============-=================================
ii  binutils       2.29.1-4ubun amd64        GNU assembler, linker and binary 

$ lsb_release -a
No LSB modules are available.
Distributor ID:	Ubuntu
Description:	Ubuntu 17.10
Release:	17.10
Codename:	artful

[bukzor]

@fornwall I'm most interested to see if this eases my pain when clang is compiled using this.
Is there some reasonable way for me to try that myself? Perhaps a wiki page somewhere?

[sjackman]

Good to know!