On Tue, Jun 25, 2024 at 06:46:04PM +0200, Bruno Haible wrote: > > Building shared libraries which depend upon > > other libraries breaks whenever a dependency found (by something like > > AC_SEARCH_LIBS) was not built with -fPIC (or whatever > > the name of this option might be on the platform in question). > > And, preferably, one might want to check that the dependency is > > a dynamic library itself. > > > > Are there any gnulib (or autoconf) macros available which can help here? > > None that I know of. > > You might get better feedback from a libtool mailing list than from here. > But my understanding is that > > 1) Static libraries are generally built without -fPIC. Building static > libraries with -fPIC was commonly done in the 1990ies, because ELF > and its dependency mechanisms were not in use everywhere at that time. > Since the time shared libraries work fine, there is hardly any use any > more to position-independent static code (except, of course, on systems > where everything is compiled with -fPIE). > > 2) libtool adds an option --with-pic to the generated configure script of a > package. But hardly anyone makes use of it. > > 3) Many packages come only with a shared library, not with a .a file any > more. See: > $ ll /usr/lib/x86_64-linux-gnu/lib*.so | wc -l > 422 > $ ll /usr/lib/x86_64-linux-gnu/lib*.a | wc -l > 207 > > The reason is that distros prefer shared libraries: When there is a > bug fix to a package, they have to rebuild that one package and not > also a dozen of other packages. > > 4) On x86, it was possible to put non-PIC code into a shared library, and > that worked (albeit with a performance hit). On x86_64, this does not > work any more. And despite of that, the fact that most static libraries > are not built with -fPIC does not hurt anyone (apparently). > > > Thinking of writing such a macro myself > > I think it would not really be useful. Your time is better spent in making > all packages that currently ship only a static library ship a shared library > as well.
Unfortunately there are cases where maintainers have building shared
libs turned off by default, and do not provide any meaningful way to query
the configuration. (Typically they are not using autotools or cmake or
anything which makes building shared libraries easy)
And they won't consider changing this :-(
As a result we (SageMath) get complaints such as: "I built such and such
library myself, with default settings, and installed it in /usr/local, and now
I get that
'recompile with -fPIC enabled' error popping out mid-build".
Would such a macro be not much more than an appropriately wrapped call
to dlopen() ? (We don't do Windows, so the latter is not an obstacle)
As I matter of fact, I wrote a while ago a more complicated macro, where
I extract the absolute path to a library. We ended up not using it.
AC_DEFUN([SAGE_ABSOLUTE_LIB], [
dnl
dnl ARG1 - the name of the dynamic library to find absolute name of
dnl ARG2 - a function in the library to test for
dnl
AC_MSG_CHECKING([[absolute path to lib]$1[...]])
AC_LANG_PUSH(C)
ABS_LIB_SAVED_LIBS=$LIBS
LIBS="[-l]$1[ -ldl]"
AC_RUN_IFELSE([
AC_LANG_PROGRAM(
[[
#include <stdio.h>
#define __USE_GNU
#include <dlfcn.h>
#ifdef __APPLE__
#define EXT "dylib"
#else
#define EXT "so"
#endif
]],
dnl run as $ cc -o conftest conftest.c -lARG1 -ldl && ./conftest
dnl output should be like /usr/lib/x86_64-linux-gnu/libARG1.so
[[ /* int main()... */
Dl_info info;
int res;
void *ha;
void *z = dlopen("lib$1."EXT, RTLD_LAZY); /* load libARG1 */
if (z) {
ha = dlsym(z, "$2"); /* get address of inflateEnd in libz
*/
res = dladdr(ha, &info); /* get info for the function
*/
printf("%s\n", info.dli_fname);
return 0; /* dladdr return value on success is
platform-dependent */
}
printf("dlopen() call failed!\n");
return 1;
]])], [
[computed_]$1[libdir]=`./conftest$EXEEXT`
AC_MSG_RESULT([ got it: "$[computed_]$1[libdir]"])
], [
AC_MSG_RESULT([ failure.])
[computed_]$1[libdir]="/usr/lib"dnl a pretty random choice
])
LIBS=$ABS_LIB_SAVED_LIBS
AC_LANG_POP(C)
])
Dima
>
> Bruno
>
>
>
>
signature.asc
Description: PGP signature
