+.\" %%%LICENSE_START(PUBLIC_DOMAIN)
.\" This is in the public domain
-.TH LD.SO 8 2012-03-06 "GNU" "Linux Programmer's Manual"
+.\" %%%LICENSE_END
+.\"
+.TH LD.SO 8 2014-01-08 "GNU" "Linux Programmer's Manual"
.SH NAME
ld.so, ld-linux.so* \- dynamic linker/loader
.SH SYNOPSIS
.B ld-linux.so*
handles ELF (\fI/lib/ld-linux.so.1\fP for libc5, \fI/lib/ld-linux.so.2\fP
for glibc2), which everybody has been using for years now.
-Otherwise both have the same behavior, and use the same
+Otherwise, both have the same behavior, and use the same
support files and programs
.BR ldd (1),
.BR ldconfig (8)
and
.IR /etc/ld.so.conf .
.LP
-The shared libraries needed by the program are searched for
-in the following order:
+When resolving library dependencies,
+the dynamic linker first inspects each dependency
+string to see if it contains a slash (this can occur if
+a library pathname containing slashes was specified at link time).
+If a slash is found, then the dependency string is interpreted as
+a (relative or absolute) pathname,
+and the library is loaded using that pathname.
+.LP
+If a library dependency does not contain a slash,
+then it is searched for in the following order:
.IP o 3
(ELF only) Using the directories specified in the
DT_RPATH dynamic section attribute
of the binary if present.
.IP o
From the cache file
-.I /etc/ld.so.cache
+.IR /etc/ld.so.cache ,
which contains a compiled list of candidate libraries previously found
in the augmented library path.
If, however, the binary was linked with the
.B \-z nodeflib
linker option, libraries in the default library paths are skipped.
+Libraries installed in hardware capability directories (see below)
+are preferred to other libraries.
.IP o
In the default path
.IR /lib ,
If the binary was linked with the
.B \-z nodeflib
linker option, this step is skipped.
-.SS $ORIGIN and rpath
+.SS Rpath token expansion
.PP
.B ld.so
-understands the string
-.I $ORIGIN
-(or equivalently
-.IR ${ORIGIN} )
-in an rpath specification (DT_RPATH or DT_RUNPATH) to mean
+understands certain strings in an rpath specification (DT_RPATH or DT_RUNPATH); those strings are substituted as follows
+.TP
+.IR $ORIGIN " (or equivalently " ${ORIGIN} )
+This expands to
the directory containing the application executable.
Thus, an application located in
.I somedir/app
could be compiled with
-.I gcc -Wl,-rpath,\(aq$ORIGIN/../lib\(aq
+
+ gcc \-Wl,\-rpath,\(aq$ORIGIN/../lib\(aq
+
so that it finds an associated shared library in
.I somedir/lib
no matter where
do not need to be installed into special directories,
but can instead be unpacked into any directory
and still find their own shared libraries.
-.\" ld.so also understands $LIB, with the same meaning as $ORIGIN/lib,
-.\" it appears.
-.\"
-.\" There is also $PLATFORM. This is a kind of wildcard
-.\" of directories related at AT_HWCAP. To get an idea of the
-.\" places that $PLATFORM would match, look at the output of the
-.\" following:
+.TP
+.IR $LIB " (or equivalently " ${LIB} )
+This expands to
+.I lib
+or
+.I lib64
+depending on the architecture
+(e.g., on x86-64, it expands to
+.IR lib64
+and
+on x86-32, it expands to
+.IR lib ).
+.TP
+.IR $PLATFORM " (or equivalently " ${PLATFORM} )
+This expands to a string corresponding to the processor type
+of the host system (e.g., "x86_64").
+On some architectures, the Linux kernel doesn't provide a platform
+string to the dynamic linker.
+The value of this string is taken from the
+.BR AT_PLATFORM
+value in the auxiliary vector (see
+.BR getauxval (3)).
+.\" To get an idea of the places that $PLATFORM would match,
+.\" look at the output of the following:
.\"
-.\" mkdir /tmp/d
-.\" LD_LIBRARY_PATH=/tmp/d strace -e open /bin/date 2>&1 | grep /tmp/d
+.\" mkdir /tmp/d
+.\" LD_LIBRARY_PATH=/tmp/d strace -e open /bin/date 2>&1 | grep /tmp/d
.\"
.\" ld.so lets names be abbreviated, so $O will work for $ORIGIN;
.\" Don't do this!!
This option is ignored if
.B ld.so
is set-user-ID or set-group-ID.
+.TP
.B \-\-audit LIST
Use objects named in LIST as auditors.
+.SH HARDWARE CAPABILITIES
+Some libraries are compiled using hardware-specific instructions which do
+not exist on every CPU.
+Such libraries should be installed in directories whose names define the
+required hardware capabilities, such as
+.IR /usr/lib/sse2/ .
+The dynamic linker checks these directories against the hardware of the
+machine and selects the most suitable version of a given library.
+Hardware capability directories can be cascaded to combine CPU features.
+The list of supported hardware capability names depends on the CPU.
+The following names are currently recognized:
+.TP
+.B Alpha
+ev4, ev5, ev56, ev6, ev67
+.TP
+.B MIPS
+loongson2e, loongson2f, octeon, octeon2
+.TP
+.B PowerPC
+4xxmac, altivec, arch_2_05, arch_2_06, booke, cellbe, dfp, efpdouble, efpsingle,
+fpu, ic_snoop, mmu, notb, pa6t, power4, power5, power5+, power6x, ppc32, ppc601,
+ppc64, smt, spe, ucache, vsx
+.TP
+.B SPARC
+flush, muldiv, stbar, swap, ultra3, v9, v9v, v9v2
+.TP
+.B s390
+dfp, eimm, esan3, etf3enh, g5, highgprs, hpage, ldisp, msa, stfle,
+z900, z990, z9-109, z10, zarch
+.TP
+.B x86 (32-bit only)
+acpi, apic, clflush, cmov, cx8, dts, fxsr, ht, i386, i486, i586, i686, mca, mmx,
+mtrr, pat, pbe, pge, pn, pse36, sep, ss, sse, sse2, tm
.SH ENVIRONMENT
-There are four important environment variables.
+Among the more important environment variables are the following:
+.TP
+.B LD_ASSUME_KERNEL
+(glibc since 2.2.3)
+Each shared library can inform the dynamic linker of the minimum kernel ABI
+version that it requires.
+(This requirement is encoded in an ELF note section that is viewable via
+.IR "readelf\ \-n"
+as a section labeled
+.BR NT_GNU_ABI_TAG .)
+At run time,
+the dynamic linker determines the ABI version of the running kernel and
+will reject loading shared libraries that specify minimum ABI versions
+that exceed that ABI version.
+
+.BR LD_ASSUME_KERNEL
+can be used to
+cause the dynamic linker to assume that it is running on a system with
+a different kernel ABI version.
+For example, the following command line causes the
+dynamic linker to assume it is running on Linux 2.2.5 when loading
+the shared libraries required by
+.IR myprog :
+
+.in +4n
+.nf
+$ \fBLD_ASSUME_KERNEL=2.2.5 ./myprog\fP
+.fi
+.in
+
+On systems that provide multiple versions of a shared library
+(in different directories in the search path) that have
+different minimum kernel ABI version requirements,
+.BR LD_ASSUME_KERNEL
+can be used to select the version of the library that is used
+(dependent on the directory search order).
+Historically, the most common use of the
+.BR LD_ASSUME_KERNEL
+feature was to manually select the older
+LinuxThreads POSIX threads implementation on systems that provided both
+LinuxThreads and NPTL
+(which latter was typically the default on such systems);
+see
+.BR pthreads (7).
+.TP
+.B LD_BIND_NOT
+(glibc since 2.2)
+Don't update the Global Offset Table (GOT) and Procedure Linkage Table (PLT)
+when resolving a symbol.
.TP
.B LD_BIND_NOW
(libc5; glibc since 2.1.1)
Similar to the
.B PATH
environment variable.
+Ignored in set-user-ID and set-group-ID programs.
.TP
.B LD_PRELOAD
-A whitespace-separated list of additional, user-specified, ELF shared
+A list of additional, user-specified, ELF shared
libraries to be loaded before all others.
+The items of the list can be separated by spaces or colons.
This can be used to selectively override functions in other shared libraries.
+The libraries are searched for using the rules given under DESCRIPTION.
For set-user-ID/set-group-ID ELF binaries,
-only libraries in the standard search
-directories that are also set-user-ID will be loaded.
+preload pathnames containing slashes are ignored,
+and libraries in the standard search directories are loaded
+only if the set-user-ID permission bit is enabled on the library file.
.TP
.B LD_TRACE_LOADED_OBJECTS
(ELF only)
.TP
.B LD_DEBUG_OUTPUT
(glibc since 2.1)
-File where
+File in which
.B LD_DEBUG
-output should be fed into, default is standard output.
+output should be written.
+The default is standard error.
.B LD_DEBUG_OUTPUT
is ignored for set-user-ID/set-group-ID binaries.
.TP
(glibc since 2.1)
If set to a nonempty string,
output symbol versioning information about the
-program if querying information about the program (i.e., either
+program if the
.B LD_TRACE_LOADED_OBJECTS
-has been set, or
-.B \-\-list
-or
-.B \-\-verify
-options have been given to the dynamic linker).
+environment variable has been set.
.TP
.B LD_WARN
(ELF only)(glibc since 2.1.3)
libraries and an ordered list of candidate libraries.
.TP
.I /etc/ld.so.preload
-File containing a whitespace separated list of ELF shared libraries to
+File containing a whitespace-separated list of ELF shared libraries to
be loaded before the program.
.TP
.B lib*.so*
ELF functionality is available since Linux 1.1.52 and libc5.
.SH SEE ALSO
.BR ldd (1),
+.BR getauxval (3),
.BR rtld-audit (7),
-.BR ldconfig (8)
+.BR ldconfig (8),
+.BR sln (8)
.\" .SH AUTHORS
.\" ld.so: David Engel, Eric Youngdale, Peter MacDonald, Hongjiu Lu, Linus
.\" Torvalds, Lars Wirzenius and Mitch D'Souza
.\" ld-linux.so: Roland McGrath, Ulrich Drepper and others.
.\"
.\" In the above, (libc5) stands for David Engel's ld.so/ld-linux.so.
+.SH COLOPHON
+This page is part of release 3.68 of the Linux
+.I man-pages
+project.
+A description of the project,
+information about reporting bugs,
+and the latest version of this page,
+can be found at
+\%http://www.kernel.org/doc/man\-pages/.
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