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 ‘AT_’ values in elf.h. Some of the data is provided
by the kernel for libc consumption, and may be obtained by ordinary
interfaces, such as sysconf. However, on a platform-by-platform
basis there may be information that is not available any other way.
getauxvalunsigned long int getauxval (unsigned long int type) ¶Preliminary: | MT-Safe | AS-Safe | AC-Safe | See POSIX Safety Concepts.
This function is used to inquire about the entries in the auxiliary
vector. The type argument should be one of the ‘AT_’ symbols
defined in elf.h. If a matching entry is found, the value is
returned; if the entry is not found, zero is returned and errno is
set to ENOENT.
For some platforms, the key 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 ‘HWCAP_’
values masked together that describe the capabilities of the cpu on which
the program is being executed.