Add <sys/auxv.h> and getauxval.

1 files changed, 29 insertions, 1 deletions

diff --git a/manual/startup.texi b/manual/startup.texi
index ed75e7b..0420e93 100644
--- a/manual/startup.texi
+++ b/manual/startup.texi
@@ -34,8 +34,9 @@ This chapter looks at program startup from the execee's point of view.  To
 see the event from the execor's point of view, see @ref{Executing a File}.
 
 @menu
-* Program Arguments::           Parsing your program's command-line arguments.
+* Program Arguments::           Parsing your program's command-line arguments
 * Environment Variables::       Less direct parameters affecting your program
+* Auxiliary Vector::            Least direct parameters affecting your program
 * System Calls::                Requesting service from the system
 * Program Termination::         Telling the system you're done; return status
 @end menu
@@ -590,6 +591,33 @@ reordering of command line arguments by @code{getopt} and
 @c !!! GNU also has COREFILE, CORESERVER, EXECSERVERS
 @end table
 
+@node Auxiliary Vector
+@section Auxiliary Vector
+@cindex auxiliary vector
+
+When a program is executed, it receives information from the operating
+system about the environment in which it is operating.  The form of this
+information is a table of key-value pairs, where the keys are from the
+set of @samp{AT_} values in @file{elf.h}.  Some of the data is provided
+by the kernel for libc consumption, and may be obtained by ordinary
+interfaces, such as @code{sysconf}.  However, on a platform-by-platform
+basis there may be information that is not available any other way.
+
+@subsection Definition of @code{getauxval}
+@comment sys/auxv.h
+@deftypefun {unsigned long int} getauxval (unsigned long int @var{type})
+This function is used to inquire about the entries in the auxiliary
+vector.  The @var{type} argument should be one of the @samp{AT_} symbols
+defined in @file{elf.h}.  If a matching entry is found, the value is
+returned; if the entry is not found, zero is returned.
+@end deftypefun
+
+For some platforms, the key @code{AT_HWCAP} is the easiest way to inquire
+about any instruction set extensions available at runtime.  In this case,
+there will (of necessity) be a platform-specific set of @samp{HWCAP_}
+values masked together that describe the capabilities of the cpu on which
+the program is being executed.
+
 @node System Calls
 @section System Calls