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bug#38610: Two libtool 2.4.6 issues


From: Roumen Petrov
Subject: bug#38610: Two libtool 2.4.6 issues
Date: Sun, 15 Dec 2019 12:03:45 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Firefox/52.0 SeaMonkey/2.49.5

Hello,

Sergey Poznyakoff wrote:
Dear maintainers,

When working on GNU mailutils we have discovered two issues with libtool,
which probably qualify as bugs.
[SNIP]

Build with installed library into non-default locations most of the time is painful.

In one of models each library set(package) is installed in separate directory in format like this: <install>/<package>-<version>. This model prevents load of headers and library from unexpected location but build use many -I and -L flags. Let skip -R/-rpath flags for simplify.

Another model is installation in common path. In this case flags are less but build is more tricky - user must ensure precedence of headers (-I) and libraries (-L) from source tree.

So report is for libtool and samples are for libraries but case is applicable for header files as well. And for headers we cannot blame libtool.

Tips:
I prefer first model but in one case I use second.
Let headers are in <INSTALL>/include and libraries are in <INSTALL>/lib
In the second with limited number of projects:
- if build uses shell script to return path to headers and libraries script must be modified do not output -I and -L flags. - if build uses pkgconfig environment must be set so that command do not output -I and -L flags. - libtool is tuned with new "system library path" : variable lt_cv_sys_lib_dlsearch_path_spec, work fine on unixes. - CC is overridden to use flags like --sysroot, -isystem, -B and etc. Unfortunately clang lack flag to add item to "system library search path" and so gcc is preferred.


Remark:
In one of the provided samples is hard coded path -L $(libdir), i.e. -L<path> -l<lib> This should be $(FOO_LIBS) and depending from model at configuration time is should be set either to -L<path> -l<lib> or only to -l<lib>. First is usable for model with separate directories otherwise should be used second one.


Regards,
Roumen Petrov

P.S. samples:
$ pkg-config --libs openssl
-lssl -lcrypto
$ PKG_CONFIG_SYSTEM_LIBRARY_PATH=/bon/go pkg-config --libs openssl
-L/usr/lib64 -lssl -lcrypto

So with PKG_CONFIG_* environment variables build could be tuned to exclude -I and -L flags.
Note pkg-config flags lib-only* and cflags-only* are out of scope.








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