[v2,1/2] manual: Document ld.so --list-diagnostics output

---
v2: Drop Python code.  @cindex/@item fix as suggested by Arsen.

 manual/dynlink.texi | 207 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 207 insertions(+)


base-commit: 65a5112ede9ba3e37e165cf6c9c432f46b903936

LGTM, thanks.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

On 23/08/23 04:00, Florian Weimer via Libc-alpha wrote:
> ---
> v2: Drop Python code.  @cindex/@item fix as suggested by Arsen.
> 
>  manual/dynlink.texi | 207 ++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 207 insertions(+)
> 
> diff --git a/manual/dynlink.texi b/manual/dynlink.texi
> index 45bf5a5b55..df41c56bfc 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
>  
> 
> base-commit: 65a5112ede9ba3e37e165cf6c9c432f46b903936