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authorUlrich Sibiller <uli42@gmx.de>2019-09-28 21:32:07 +0200
committerMihai Moldovan <ionic@ionic.de>2019-10-10 12:45:23 +0200
commitb55c66e8ab3ed004043c54101aae8935ca7471eb (patch)
treeb48c475789ad717339b0bbddcb480160431c7ceb /nx-X11/programs/Xserver/hw/nxagent/Imakefile
parent57d3a42c22f7213e782f89429c1a072833f90785 (diff)
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nxagent/Imakefile: remove ../../exports/lib
nxagent links system libraries that link against libX11. Unfortunately, nxagent (and libXcompshad) require a modified libX11 version, nicknamed libNX_X11, for proper functioning. Fortunately, this one can act as a drop-in replacement for the system libX11. So we’ll hack our way out: add a DT_NEEDED entry for libX11 by linking against the system library when building nxagent and link the other system libraries later and set DT_RUNPATH to a special directory containing symlinks from libNX_X11 to libX11. This tricks the loader into pulling in the "fake" libX11 version without checking its SONAME and thus satisfying the DT_NEEDED entry early on - specifically also for the system libraries. Ex.: readelf -a /usr/bin/nxagent | grep NEEDED 0x0000000000000001 (NEEDED) Shared library: [libX11.so.6] ... 0x0000000000000001 (NEEDED) Shared library: [libNX_X11.so.6] ... If, however, you run the build a second time, it will find the newly created libX11 links in ../../exports/lib (used as an additional library search path) instead of the system libX11. The results in a binary looking like this: 0x0000000000000001 (NEEDED) Shared library: [libNX_X11.so.6] ... With such a setup, the whole magic falls apart and system libraries will suddenly pull in the actual system libX11 file. We initially believed a compiler call such as: ${CC} [--unrelated-options ...] [-Lunrelated_library_path ...] -lX11 [more options like -l and -L] -L../../exports/lib -lother_libraries to do "the right thing" and link against the system libX11 (or, at worst, a libX11 found in the library directory search list preceding the link call) and use ../../exports/lib only for later linking operations, since the order of options matters. However, this turned out to be blatantly wrong: while the order of -L arguments does matter for building the search path, the whole search path including elements from *ALL* -L arguments (and the system paths) will always be used when linking libraries. Hence, (counter-intuitively to us) both these calls will be equivalent: ${CC} [--unrelated-options ...] -la -Loverride_liba -lb [-Lunrelated_library_path ...] -lc ${CC} [--unrelated-options ...] -Loverride_liba [-Lunrelated_library_path ...] -la -lb -lc By removing LDPRELIBS from NXAGENTSYSLIBS, ../../exports/lib is no longer used during building/linking and the binaries are built reproducibly. We never intended to use this directory at link time anyway.
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