cnf/make.conf.example.riscv.diff

--- make.conf.example
+++ make.conf.example
@@ -22,6 +22,15 @@
 # Example:
 #USE="X gtk gnome -alsa"
 
+# Host Setting
+# ===========
+#
+# All RV64 systems should use this host setting:
+CHOST="riscv64-unknown-linux-gnu"
+
+# whereas all RV32 ones should use:
+#CHOST="riscv32-unknown-linux-gnu"
+
 # Host and optimization settings
 # ==============================
 #
@@ -39,9 +48,31 @@
 # -frecord-gcc-switches, since otherwise the check could result in false
 # positive results.
 #
-# Please refer to the GCC manual for a list of possible values.
+# -mcpu=<cpu-type> tells the compiler to take full advantage of the ABI and
+# instructions available on a certain CPU. This will produce code which may
+# not run on other RISC-V CPUs, even if they support the same ISA.
+#
+# -mtune=<cpu-type-or-series> results in code optimised for a specific CPU
+# (e.g. SiFive U74) or family (e.g. the SiFive 7 series) without breaking
+# compatibility with other RISC-V CPUs supporting the same ISA.
+#
+# -march=<isa-string> specifies the exact ISA for which to generate code.
+# This is normally not needed if you set -mcpu but might be useful for CPUs
+# not explicitly supported by gcc yet. Should that be the case and you aren't
+# sure what ISA string to use, the output of /proc/cpuinfo might give you a hint.
+#
+# -mabi=<abi-string> specifies the integer and floating-point calling convention
+# to use. Again, this is normally not needed if you set -mcpu. Care should be
+# taken while setting both -march and -mabi, as some calling conventions are
+# impossible to implement on some ISAs.
+#
+# Please refer to the section "RISC-V Options" of the GCC manual for a list
+# of possible ABI, architecture, CPU and feature values.
+#
+# Decent examples:
 #
-#CFLAGS="-O2 -pipe"
+#CFLAGS="-mcpu=sifive-u74 -O2 -pipe"
+#CFLAGS="-mtune=sifive-7-series -O2 -pipe"
 #
 # If you set a CFLAGS above, then this line will set your default C++ flags to
 # the same settings.
@@ -76,7 +107,7 @@
 # DO NOT PUT ANYTHING BUT YOUR SPECIFIC ~ARCHITECTURE IN THE LIST.
 # IF YOU ARE UNSURE OF YOUR ARCH, OR THE IMPLICATIONS, DO NOT MODIFY THIS.
 #
-#ACCEPT_KEYWORDS="~arch"
+#ACCEPT_KEYWORDS="~riscv"
 
 # ACCEPT_LICENSE is used to mask packages based on licensing restrictions.
 # It may contain both license and group names, where group names are