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diff --git a/manual/dynlink.texi b/manual/dynlink.texi index 45bf5a5..df41c56 100644 --- a/manual/dynlink.texi +++ b/manual/dynlink.texi @@ -13,9 +13,216 @@ as plugins) later at run time. Dynamic linkers are sometimes called @dfn{dynamic loaders}. @menu +* Dynamic Linker Invocation:: Explicit invocation of the dynamic linker. * Dynamic Linker Introspection:: Interfaces for querying mapping information. @end menu +@node Dynamic Linker Invocation + +@cindex program interpreter +When a dynamically linked program starts, the operating system +automatically loads the dynamic linker along with the program. +@Theglibc{} also supports invoking the dynamic linker explicitly to +launch a program. This command uses the implied dynamic linker +(also sometimes called the @dfn{program interpreter}): + +@smallexample +sh -c 'echo "Hello, world!"' +@end smallexample + +This command specifies the dynamic linker explicitly: + +@smallexample +ld.so /bin/sh -c 'echo "Hello, world!"' +@end smallexample + +Note that @command{ld.so} does not search the @env{PATH} environment +variable, so the full file name of the executable needs to be specified. + +The @command{ld.so} program supports various options. Options start +@samp{--} and need to come before the program that is being launched. +Some of the supported options are listed below. + +@table @code +@item --list-diagnostics +Print system diagnostic information in a machine-readable format. +@xref{Dynamic Linker Diagnostics}. +@end table + +@menu +* Dynamic Linker Diagnostics:: Obtaining system diagnostic information. +@end menu + +@node Dynamic Linker Diagnostics +@section Dynamic Linker Diagnostics +@cindex diagnostics (dynamic linker) + +The @samp{ld.so --list-diagnostics} produces machine-readable +diagnostics output. This output contains system data that affects the +behavior of @theglibc{}, and potentially application behavior as well. + +The exact set of diagnostic items can change between releases of +@theglibc{}. The output format itself is not expected to change +radically. + +The following table shows some example lines that can be written by the +diagnostics command. + +@table @code +@item dl_pagesize=0x1000 +The system page size is 4096 bytes. + +@item env[0x14]="LANG=en_US.UTF-8" +This item indicates that the 21st environment variable at process +startup contains a setting for @code{LANG}. + +@item env_filtered[0x22]="DISPLAY" +The 35th environment variable is @code{DISPLAY}. Its value is not +included in the output for privacy reasons because it is not recognized +as harmless by the diagnostics code. + +@item path.prefix="/usr" +This means that @theglibc{} was configured with @code{--prefix=/usr}. + +@item path.system_dirs[0x0]="/lib64/" +@itemx path.system_dirs[0x1]="/usr/lib64/" +The built-in dynamic linker search path contains two directories, +@code{/lib64} and @code{/usr/lib64}. +@end table + +@subsection Dynamic Linker Diagnostics Output Format + +As seen above, diagnostic lines assign values (integers or strings) to a +sequence of labeled subscripts, separated by @samp{.}. Some subscripts +have integer indices associated with them. The subscript indices are +not necessarily contiguous or small, so an associative array should be +used to store them. Currently, all integers fit into the 64-bit +unsigned integer range. Every access path to a value has a fixed type +(string or integer) independent of subscript index values. Likewise, +whether a subscript is indexed does not depend on previous indices (but +may depend on previous subscript labels). + +A syntax description in ABNF (RFC 5234) follows. Note that +@code{%x30-39} denotes the range of decimal digits. Diagnostic output +lines are expected to match the @code{line} production. + +@c ABNF-START +@smallexample +HEXDIG = %x30-39 / %x61-6f ; lowercase a-f only +ALPHA = %x41-5a / %x61-7a / %x7f ; letters and underscore +ALPHA-NUMERIC = ALPHA / %x30-39 / "_" +DQUOTE = %x22 ; " + +; Numbers are always hexadecimal and use a 0x prefix. +hex-value-prefix = %x30 %x78 +hex-value = hex-value-prefix 1*HEXDIG + +; Strings use octal escape sequences and \\, \". +string-char = %x20-21 / %x23-5c / %x5d-7e ; printable but not "\ +string-quoted-octal = %x30-33 2*2%x30-37 +string-quoted = "\" ("\" / DQUOTE / string-quoted-octal) +string-value = DQUOTE *(string-char / string-quoted) DQUOTE + +value = hex-value / string-value + +label = ALPHA *ALPHA-NUMERIC +index = "[" hex-value "]" +subscript = label [index] + +line = subscript *("." subscript) "=" value +@end smallexample + +@subsection Dynamic Linker Diagnostics Values + +As mentioned above, the set of diagnostics may change between +@theglibc{} releases. Nevertheless, the following table documents a few +common diagnostic items. All numbers are in hexadecimal, with a +@samp{0x} prefix. + +@table @code +@item dl_dst_lib=@var{string} +The @code{$LIB} dynamic string token expands to @var{string}. + +@cindex HWCAP (diagnostics) +@item dl_hwcap=@var{integer} +@itemx dl_hwcap2=@var{integer} +The HWCAP and HWCAP2 values, as returned for @code{getauxval}, and as +used in other places depending on the architecture. + +@cindex page size (diagnostics) +@item dl_pagesize=@var{integer} +The system page size is @var{integer} bytes. + +@item dl_platform=@var{string} +The @code{$PLATFORM} dynamic string token expands to @var{string}. + +@item dso.libc=@var{string} +This is the soname of the shared @code{libc} object that is part of +@theglibc{}. On most architectures, this is @code{libc.so.6}. + +@item env[@var{index}]=@var{string} +@itemx env_filtered[@var{index}]=@var{string} +An environment variable from the process environment. The integer +@var{index} is the array index in the environment array. Variables +under @code{env} include the variable value after the @samp{=} (assuming +that it was present), variables under @code{env_filtered} do not. + +@item path.prefix=@var{string} +This indicates that @theglibc{} was configured using +@samp{--prefix=@var{string}}. + +@item path.sysconfdir=@var{string} +@Theglibc{} was configured (perhaps implicitly) with +@samp{--sysconfdir=@var{string}} (typically @code{/etc}). + +@item path.system_dirs[@var{index}]=@var{string} +These items list the elements of the built-in array that describes the +default library search path. The value @var{string} is a directory file +name with a trailing @samp{/}. + +@item path.rtld=@var{string} +This string indicates the application binary interface (ABI) file name +of the run-time dynamic linker. + +@item version.release="stable" +@itemx version.release="development" +The value @code{"stable"} indicates that this build of @theglibc{} is +from a release branch. Releases labeled as @code{"development"} are +unreleased development versions. + +@cindex version (diagnostics) +@item version.version="@var{major}.@var{minor}" +@itemx version.version="@var{major}.@var{minor}.9000" +@Theglibc{} version. Development releases end in @samp{.9000}. + +@cindex auxiliary vector (diagnostics) +@item auxv[@var{index}].a_type=@var{type} +@itemx auxv[@var{index}].a_val=@var{integer} +@itemx auxv[@var{index}].a_val_string=@var{string} +An entry in the auxiliary vector (specific to Linux). The values +@var{type} (an integer) and @var{integer} correspond to the members of +@code{struct auxv}. If the value is a string, @code{a_val_string} is +used instead of @code{a_val}, so that values have consistent types. + +The @code{AT_HWCAP} and @code{AT_HWCAP2} values in this output do not +reflect adjustment by @theglibc{}. + +@item uname.sysname=@var{string} +@itemx uname.nodename=@var{string} +@itemx uname.release=@var{string} +@itemx uname.version=@var{string} +@itemx uname.machine=@var{string} +@itemx uname.domain=@var{string} +These Linux-specific items show the values of @code{struct utsname}, as +reported by the @code{uname} function. @xref{Platform Type}. + +@cindex CPUID (diagnostics) +@item x86.cpu_features.@dots{} +These items are specific to the i386 and x86-64 architectures. They +reflect supported CPU features and information on cache geometry, mostly +collected using the @code{CPUID} instruction. +@end table + @node Dynamic Linker Introspection @section Dynamic Linker Introspection |