Makefile: use root-relative -f path for /sbin/ldconfig

Without this, the -f path argument is ignored:

 $ strace -f -s128 /sbin/ldconfig -r /home/vagrant/buildroot/output/target -f /home/vagrant/buildroot/output/target/etc/ld.so.conf |& grep "ld\.so\.conf"
 execve("/sbin/ldconfig", ["/sbin/ldconfig", "-r", "/home/vagrant/buildroot/output/target", "-f", "/home/vagrant/buildroot/output/target/etc/ld.so.conf"], [/* 61 vars */]) = 0
 execve("/sbin/ldconfig.real", ["/sbin/ldconfig.real", "-r", "/home/vagrant/buildroot/output/target", "-f", "/home/vagrant/buildroot/output/target/etc/ld.so.conf"], [/* 61 vars */]) = 0
 write(2, "Warning: ignoring configuration file that cannot be opened: /home/vagrant/buildroot/output/target/etc/ld.so.conf", 112Warning: ignoring configuration file that cannot be opened: /home/vagrant/buildroot/output/target/etc/ld.so.conf) = 112

Proof that using root-relative path -f path (/etc/ld.so.conf, without $(TARGET_DIR) in front) picks up the correct file:

 $ strace -f -s128 /sbin/ldconfig -r /home/vagrant/buildroot/output/target -f /etc/ld.so.conf |& grep "ld\.so\.conf"
 execve("/sbin/ldconfig", ["/sbin/ldconfig", "-r", "/home/vagrant/buildroot/output/target", "-f", "/etc/ld.so.conf"], [/* 61 vars */]) = 0
 execve("/sbin/ldconfig.real", ["/sbin/ldconfig.real", "-r", "/home/vagrant/buildroot/output/target", "-f", "/etc/ld.so.conf"], [/* 61 vars */]) = 0
 lstat("/home/vagrant/buildroot/output/target/etc/ld.so.conf", {st_mode=S_IFREG|0644, st_size=0, ...}) = 0
 open("/home/vagrant/buildroot/output/target/etc/ld.so.conf", O_RDONLY) = 3

Tested on Ubuntu 14.04.

 $ /sbin/ldconfig --version
 ldconfig (Ubuntu EGLIBC 2.19-0ubuntu6.6) 2.19
 ...

$(TARGET_CROSS)ldconfig behaves differently (at least the ldconfig I tested, which was built by Buildroot) and should not have root-relative -f path. If it does, it will pick up host /etc/ld.so.conf file.

---
 Makefile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index dd8959f..61ce1f9 100644
@@ -607,7 +607,7 @@ endif
 					-f $(TARGET_DIR)/etc/ld.so.conf; \
 	else \
 		/sbin/ldconfig -r $(TARGET_DIR) \
-			       -f $(TARGET_DIR)/etc/ld.so.conf; \
+			       -f /etc/ld.so.conf; \
 	fi
 	( \
 		echo "NAME=Buildroot"; \

2.5.2

Needed when building in a FHS chroot on NixOS[1]. Without it, ldconfig tries to open a directory in the nix store. Being explicit fixes it.

Tested that it doesn't regress on Ubuntu 14.04.

[1] I know, it's an uncommon setup :-)

---
 Makefile | 1 +
 1 file changed, 1 insertion(+)

index 61ce1f9..ff812f3 100644
@@ -607,6 +607,7 @@ endif
 					-f $(TARGET_DIR)/etc/ld.so.conf; \
 	else \
 		/sbin/ldconfig -r $(TARGET_DIR) \
+			       -C /etc/ld.so.cache \
 			       -f /etc/ld.so.conf; \
 	fi
 	( \

2.5.2

This makes me worried that it will do the wrong thing on some other build
hosts. In fact, using /sbin/ldconfig is fundamentally broken since we can't be sure that it's compatible with the target dynamic linker.

Regards,
Arnout

Arnout Vandecappelle                          arnout at mind be
Senior Embedded Software Architect            +32-16-286500
Essensium/Mind                                http://www.mind.be
G.Geenslaan 9, 3001 Leuven, Belgium           BE 872 984 063 RPR Leuven
LinkedIn profile: http://www.linkedin.com/in/arnoutvandecappelle
GPG fingerprint:  7493 020B C7E3 8618 8DEC 222C 82EB F404 F9AC 0DDF

If you don't want to apply this patch, that is totally fine. It just fixes a warning I saw while debugging an issue that ended up being fixed by the next patch:

[PATCH 2/2] Makefile: add -C flag for /sbin/ldconfig

The 2nd patch is the one I really care about, it currently blocks me from running Buildroot in my preferred environment.

If you want to completely remove use of (host) /sbin/ldconfig, that's fine too.

Just tell me what to do :-)

- Bj?rn

Dear Bj?rn Forsman,

We need to completely remove the ldconfig stuff, since it simply cannot work. However, there is at least one package (mysql) that installs libraries in a non-standard location (/usr/lib/mysql) and relies on ld.so.conf for the dynamic linker to find them. I believe we need to fix MySQL so that it installs its libraries in /usr/lib, and then get rid of all the ldconfig/ld.so.conf stuff.

Or, alternatively, see how to get it working with an init script which runs ldconfig at boot time. But then you have to look at how uClibc and musl handle this, and implement a solution that works for all three C libraries.

Best regards,

Thomas

Thomas Petazzoni, CTO, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

Hi Thomas,

Sounds like a bigger task than I planned... :-/ (I'm afraid to break things.)

Would it be possible to merge "[PATCH 2/2] Makefile: add -C flag for /sbin/ldconfig" as a stop-gap fix for my build problem then?

- Bj?rn

Bj?rn,

As we discussed previously, our ldconfig handling is broken. So we are simply planning to remove entirely. I have just posted a patch to this effect:

	https://patchwork.ozlabs.org/patch/561618/

The idea is that from now on, packages are expected to install libraries in path that are in the default search path of the dynamic linker.

Consequently, I've marked your patches as Superseded. If you find any package that doesn't work properly following our ldconfig removal, do not hesitate to let us know.

Thanks!

Thomas

Thomas Petazzoni, CTO, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com