RISC-V: Support -mlittle-endian and -mbig-endian

gcc/
	* config/riscv/elf.h (LINK_SPEC): Pass linker endianness flag.
	* config/riscv/freebsd.h (LINK_SPEC): Likewise.
	* config/riscv/linux.h (LINK_SPEC): Likewise.
	* config/riscv/riscv.h (ASM_SPEC): Pass -mbig-endian and
	-mlittle-endian.
	(BYTES_BIG_ENDIAN): Handle big endian.
	(WORDS_BIG_ENDIAN): Define to BYTES_BIG_ENDIAN.
	* config/riscv/riscv.opt (-mbig-endian, -mlittle-endian): New
	options.
	* doc/invoke.texi (-mbig-endian, -mlittle-endian): Document.

gcc/config/riscv/elf.h

@@ -20,6 +20,8 @@ along with GCC; see the file COPYING3.  If not see
 #define LINK_SPEC "\
 -melf" XLEN_SPEC "lriscv \
 %{mno-relax:--no-relax} \
+%{mbig-endian:-EB} \
+%{mlittle-endian:-EL} \
 %{shared}"
 
 /* Link against Newlib libraries, because the ELF backend assumes Newlib.

gcc/config/riscv/freebsd.h

@@ -44,6 +44,8 @@ along with GCC; see the file COPYING3.  If not see
   %{p:%nconsider using `-pg' instead of `-p' with gprof (1)}	\
   %{v:-V}							\
   %{assert*} %{R*} %{rpath*} %{defsym*}				\
+  %{mbig-endian:-EB}						\
+  %{mlittle-endian:-EL}						\
   %{shared:-Bshareable %{h*} %{soname*}}			\
   %{symbolic:-Bsymbolic}					\
   %{static:-Bstatic}						\

gcc/config/riscv/linux.h

@@ -60,6 +60,8 @@ along with GCC; see the file COPYING3.  If not see
 #define LINK_SPEC "\
 -melf" XLEN_SPEC "lriscv" LD_EMUL_SUFFIX " \
 %{mno-relax:--no-relax} \
+%{mbig-endian:-EB} \
+%{mlittle-endian:-EL} \
 %{shared} \
   %{!shared: \
     %{!static: \

gcc/config/riscv/riscv.h

@@ -91,6 +91,8 @@ extern const char *riscv_default_mtune (int argc, const char **argv);
 %{" FPIE_OR_FPIC_SPEC ":-fpic} \
 %{march=*} \
 %{mabi=*} \
+%{mbig-endian} \
+%{mlittle-endian} \
 %(subtarget_asm_spec)" \
 ASM_MISA_SPEC
 
@@ -126,8 +128,8 @@ ASM_MISA_SPEC
 /* Target machine storage layout */
 
 #define BITS_BIG_ENDIAN 0
-#define BYTES_BIG_ENDIAN 0
-#define WORDS_BIG_ENDIAN 0
+#define BYTES_BIG_ENDIAN (TARGET_BIG_ENDIAN != 0)
+#define WORDS_BIG_ENDIAN (BYTES_BIG_ENDIAN)
 
 #define MAX_BITS_PER_WORD 64
 

gcc/config/riscv/riscv.opt

@@ -21,6 +21,14 @@
 HeaderInclude
 config/riscv/riscv-opts.h
 
+mbig-endian
+Target RejectNegative Mask(BIG_ENDIAN)
+Assume target CPU is configured as big endian.
+
+mlittle-endian
+Target RejectNegative InverseMask(BIG_ENDIAN)
+Assume target CPU is configured as little endian.
+
 mbranch-cost=
 Target RejectNegative Joined UInteger Var(riscv_branch_cost)
 -mbranch-cost=N	Set the cost of branches to roughly N instructions.

gcc/doc/invoke.texi

@@ -1171,6 +1171,7 @@ See RS/6000 and PowerPC Options.
 -mrelax  -mno-relax @gol
 -mriscv-attribute  -mmo-riscv-attribute @gol
 -malign-data=@var{type} @gol
+-mbig-endian  -mlittle-endian @gol
 +-mstack-protector-guard=@var{guard} -mstack-protector-guard-reg=@var{reg} @gol
 +-mstack-protector-guard-offset=@var{offset}}
 
@@ -26748,6 +26749,17 @@ types.  Supported values for @var{type} are @samp{xlen} which uses x register
 width as the alignment value, and @samp{natural} which uses natural alignment.
 @samp{xlen} is the default.
 
+@item -mbig-endian
+@opindex mbig-endian
+Generate big-endian code.  This is the default when GCC is configured for a
+@samp{riscv64be-*-*} or @samp{riscv32be-*-*} target.
+
+@item -mlittle-endian
+@opindex mlittle-endian
+Generate little-endian code.  This is the default when GCC is configured for a
+@samp{riscv64-*-*} or @samp{riscv32-*-*} but not a @samp{riscv64be-*-*} or
+@samp{riscv32be-*-*} target.
+
 @item -mstack-protector-guard=@var{guard}
 @itemx -mstack-protector-guard-reg=@var{reg}
 @itemx -mstack-protector-guard-offset=@var{offset}