The linker combines executable files and shared libraries into a runnable program. It searches library paths and the binary's RUNPATH for needed shared libraries by name. The RUNPATH is set during compile-time linking with the -R option. At runtime, the dynamic linker (ld.so.1) uses information in the binary like the NEEDED tags and RUNPATH to locate and load the required libraries when the program starts. Various debugger tools like dump, lari, and pldd can show the shared library dependencies and runtime linking information.

1. The Linker
Common Issues

2. General wisdom
Read ld.so.1(1)
Verify your
assumptions

3. What does the linker do?
Combine an executable and shared
libraries to a runnable entity

4. How does it work?
(a bit simplified...)
This is runtime linking!
Look for wanted libs in NEEDED in the object
[1] NEEDED libcurses.so.1
[2] NEEDED libintl.so.8
[3] NEEDED libiconv.so.2
Search them in system dirs
Default Library Path (ELF): /lib:/usr/lib (system default)
Trusted Directories (ELF): /lib/secure:/usr/lib/secure (system default)
and RUNPATH
[10] RUNPATH /opt/csw/lib/$ISALIST:/opt/csw/lib

5. Getting the runpath in
the binary
Read ld(1)
Always done during compile-time linking
Option „-R <path>“
LD_OPTIONS is processed before -R
This can break testsuites

6. -R or LD_OPTIONS ?
-R in LDFLAGS
Plays nice with applications
If they honour LDFLAGS
Multiple shell invocations may destroy
$ISALIST
LD_OPTIONS
Works always
May confuse build of test apps as they link
against installed libs instead of the newly
build

7. $ISALIST
Dynamically expanded by ld.so.1, e.g.
sparcv9+vis2
sparcv9+vis
sparcv9
sparcv8plus+vis2
sparcv8plus+vis
sparcv8plus
sparcv8
sparcv8-fsmuld
sparcv7
sparc
See also isalist(1)

8. Debugging
Static info from the binary
dump -Lv <binary>
dam@login [login]:/home/dam > dump -Lv /opt/csw/bin/bash
/opt/csw/bin/bash:
**** DYNAMIC SECTION INFORMATION ****
.dynamic:
[INDEX] Tag Value
[1] NEEDED libcurses.so.1
[2] NEEDED libintl.so.8
[3] NEEDED libiconv.so.2
[4] NEEDED libsocket.so.1
[5] NEEDED libnsl.so.1
[6] NEEDED libdl.so.1
[7] NEEDED libc.so.1
[8] INIT 0xce204
[9] FINI 0xce214
[10] RUNPATH /opt/csw/lib/$ISALIST:/opt/csw/lib:/opt/csw/lib:/opt/csw/lib
[11] RPATH /opt/csw/lib/$ISALIST:/opt/csw/lib:/opt/csw/lib:/opt/csw/lib
[12] HASH 0x100e8
[13] STRTAB 0x1c994
...
lari <binary>

9. Debugging
Info from the running process
pldd
dam@login [login]:/home/dam > pldd $$
3838: /opt/csw/bin/zsh
/opt/csw/lib/libgdbm.so.3.0.0
/opt/csw/lib/libpcre.so.0.0.1
/opt/csw/lib/libiconv.so.2.5.1
/lib/libsocket.so.1
/lib/libdl.so.1
/opt/csw/lib/libncursesw.so.5.9
/lib/libm.so.1
/lib/libc.so.1
/lib/libnsl.so.1
/platform/sun4v/lib/libc_psr.so.1
/opt/csw/lib/zsh/4.3.10/zsh/zle.so

10. AUXV linkage
Link option
-f <filtee>
E.g. ld -h libcurl.so.4 -f libcurl-feature.so.4 ...
How does it look in the binary?
[10] SONAME libcurl.so.4
[11] AUXILIARY libcurl-feature.so.4