[PATCH 1/2, AArch64] gas docs missing for -mcpu/-march option

[Jiong Wang <jiong dot wang at arm dot com>]

Currently, there are no -mcpu/-march documentations for AArch64.

This patch add the docs for them.

Please review.

Thanks.
Jiong

gas/

  * doc/c-aarch64.texi (AArch64 Options): Document -mcpu and -march.

diff --git a/gas/doc/c-aarch64.texi b/gas/doc/c-aarch64.texi
index 6019006..544d5ab 100644
--- a/gas/doc/c-aarch64.texi
+++ b/gas/doc/c-aarch64.texi
@@ -50,6 +50,46 @@ Specify which ABI the source code uses.  The recognized arguments
 are: @code{ilp32} and @code{lp64}, which decides the generated object
 file in ELF32 and ELF64 format respectively.  The default is @code{lp64}.
 
+@cindex @code{-mcpu=} command line option, AArch64
+@item -mcpu=@var{processor}[+@var{extension}@dots{}]
+This option specifies the target processor.  The assembler will issue an error
+message if an attempt is made to assemble an instruction which will not execute
+on the target processor.  The following processor names are recognized:
+@code{cortex-a53},
+@code{cortex-a57},
+and
+@code{xgene-1}.
+The special name @code{all} may be used to allow the assembler to accept
+instructions valid for any ARMv8 processor.
+
+In addition to the basic instruction set, the assembler can be told to accept
+various extension mnemonics that extend the processor.
+
+Multiple extensions may be specified, separated by a @code{+}.  Extension
+mnemonics may also be removed from those the assembler accepts. This is done by
+prepending @code{no} to the option that adds the extension.  Extensions that are
+removed should be listed after all extensions which have been added.
+
+The following extensions are currently supported:
+@code{crc} (Enable CRC instructions.),
+@code{crypto} (Enable cryptographic extension.  This implies @code{fp} and @code{simd}.),
+@code{fp} (Enable floating-point extension.),
+and
+@code{simd} (Enable Advanced SIMD extension, This implies @code{fp}.).
+
+@cindex @code{-march=} command line option, AArch64
+@item -march=@var{architecture}[+@var{extension}@dots{}]
+This option specifies the target architecture.  The assembler will issue an
+error message if an attempt is made to assemble an instruction which will not
+execute on the target architecture.  The only value for @var{arch} is
+@code{armv8-a}.
+
+If both @code{-mcpu} and @code{-march} are specified, the assembler will use
+the setting for @code{-mcpu}.
+
+The architecture option can be extended with the same instruction set extension
+options as the @code{-mcpu} option.
+
 @end table
 @c man end