1 2 NOTES FOR UNIX LIKE PLATFORMS 3 ============================= 4 5 For Unix/POSIX runtime systems on Windows, please see NOTES.WIN. 6 7 8 OpenSSL uses the compiler to link programs and shared libraries 9 --------------------------------------------------------------- 10 11 OpenSSL's generated Makefile uses the C compiler command line to 12 link programs, shared libraries and dynamically loadable shared 13 objects. Because of this, any linking option that's given to the 14 configuration scripts MUST be in a form that the compiler can accept. 15 This varies between systems, where some have compilers that accept 16 linker flags directly, while others take them in '-Wl,' form. You need 17 to read your compiler documentation to figure out what is acceptable, 18 and ld(1) to figure out what linker options are available. 19 20 21 Shared libraries and installation in non-default locations 22 ---------------------------------------------------------- 23 24 Every Unix system has its own set of default locations for shared 25 libraries, such as /lib, /usr/lib or possibly /usr/local/lib. If 26 libraries are installed in non-default locations, dynamically linked 27 binaries will not find them and therefore fail to run, unless they get 28 a bit of help from a defined runtime shared library search path. 29 30 For OpenSSL's application (the 'openssl' command), our configuration 31 scripts do NOT generally set the runtime shared library search path for 32 you. It's therefore advisable to set it explicitly when configuring, 33 unless the libraries are to be installed in directories that you know 34 to be in the default list. 35 36 Runtime shared library search paths are specified with different 37 linking options depending on operating system and versions thereof, and 38 are talked about differently in their respective documentation; 39 variations of RPATH are the most usual (note: ELF systems have two such 40 tags, more on that below). 41 42 Possible options to set the runtime shared library search path include 43 the following: 44 45 -Wl,-rpath,/whatever/path # Linux, *BSD, etc. 46 -R /whatever/path # Solaris 47 -Wl,-R,/whatever/path # AIX (-bsvr4 is passed internally) 48 -Wl,+b,/whatever/path # HP-UX 49 -rpath /whatever/path # Tru64, IRIX 50 51 OpenSSL's configuration scripts recognise all these options and pass 52 them to the Makefile that they build. (In fact, all arguments starting 53 with '-Wl,' are recognised as linker options.) 54 55 Please do not use verbatim directories in your runtime shared library 56 search path! Some OpenSSL config targets add an extra directory level 57 for multilib installations. To help with that, the produced Makefile 58 includes the variable LIBRPATH, which is a convenience variable to be 59 used with the runtime shared library search path options, as shown in 60 this example: 61 62 $ ./config --prefix=/usr/local/ssl --openssldir=/usr/local/ssl \ 63 '-Wl,-rpath,$(LIBRPATH)' 64 65 On modern ELF based systems, there are two runtime search paths tags to 66 consider, DT_RPATH and DT_RUNPATH. Shared objects are searched for in 67 this order: 68 69 1. Using directories specified in DT_RPATH, unless DT_RUNPATH is 70 also set. 71 2. Using the environment variable LD_LIBRARY_PATH 72 3. Using directories specified in DT_RUNPATH. 73 4. Using system shared object caches and default directories. 74 75 This means that the values in the environment variable LD_LIBRARY_PATH 76 won't matter if the library is found in the paths given by DT_RPATH 77 (and DT_RUNPATH isn't set). 78 79 Exactly which of DT_RPATH or DT_RUNPATH is set by default appears to 80 depend on the system. For example, according to documentation, 81 DT_RPATH appears to be deprecated on Solaris in favor of DT_RUNPATH, 82 while on Debian GNU/Linux, either can be set, and DT_RPATH is the 83 default at the time of writing. 84 85 How to choose which runtime search path tag is to be set depends on 86 your system, please refer to ld(1) for the exact information on your 87 system. As an example, the way to ensure the DT_RUNPATH is set on 88 Debian GNU/Linux systems rather than DT_RPATH is to tell the linker to 89 set new dtags, like this: 90 91 $ ./config --prefix=/usr/local/ssl --openssldir=/usr/local/ssl \ 92 '-Wl,--enable-new-dtags,-rpath,$(LIBRPATH)' 93 94 It might be worth noting that some/most ELF systems implement support 95 for runtime search path relative to the directory containing current 96 executable, by interpreting $ORIGIN along with some other internal 97 variables. Consult your system documentation. 98 99 Linking your application 100 ------------------------ 101 102 Third-party applications dynamically linked with OpenSSL (or any other) 103 shared library face exactly the same problem with non-default locations. 104 The OpenSSL config options mentioned above might or might not have bearing 105 on linking of the target application. "Might" means that under some 106 circumstances it would be sufficient to link with OpenSSL shared library 107 "naturally", i.e. with -L/whatever/path -lssl -lcrypto. But there are 108 also cases when you'd have to explicitly specify runtime search path 109 when linking your application. Consult your system documentation and use 110 above section as inspiration... 111 112 Shared OpenSSL builds also install static libraries. Linking with the 113 latter is likely to require special care, because linkers usually look 114 for shared libraries first and tend to remain "blind" to static OpenSSL 115 libraries. Referring to system documentation would suffice, if not for 116 a corner case. On AIX static libraries (in shared build) are named 117 differently, add _a suffix to link with them, e.g. -lcrypto_a. 118