MIPS: End asm function prologue macros with .insn

When building a kernel targeting a microMIPS ISA, recent GNU linkers
will fail the link if they cannot determine that the target of a branch
or jump is microMIPS code, with errors such as the following:

    mips-img-linux-gnu-ld: arch/mips/built-in.o: .text+0x542c:
    Unsupported jump between ISA modes; consider recompiling with
    interlinking enabled.
    mips-img-linux-gnu-ld: final link failed: Bad value

or:

    ./arch/mips/include/asm/uaccess.h:1017: warning: JALX to a
    non-word-aligned address

Placing anything other than an instruction at the start of a function
written in assembly appears to trigger such errors. In order to prepare
for allowing us to follow function prologue macros with an EXPORT_SYMBOL
invocation, end the prologue macros (LEAD, NESTED & FEXPORT) with a
.insn directive. This ensures that the start of the function is marked
as code, which always makes sense for functions & safely prevents us
from hitting the link errors described above.
Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Reviewed-by: Maciej W. Rozycki <macro@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/14508/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/include/asm/asm.h

@@ -54,7 +54,8 @@
 		.align	2;				\
 		.type	symbol, @function;		\
 		.ent	symbol, 0;			\
-symbol:		.frame	sp, 0, ra
+symbol:		.frame	sp, 0, ra;			\
+		.insn
 
 /*
  * NESTED - declare nested routine entry point
@@ -63,8 +64,9 @@ symbol:		.frame	sp, 0, ra
 		.globl	symbol;				\
 		.align	2;				\
 		.type	symbol, @function;		\
-		.ent	symbol, 0;			 \
-symbol:		.frame	sp, framesize, rpc
+		.ent	symbol, 0;			\
+symbol:		.frame	sp, framesize, rpc;		\
+		.insn
 
 /*
  * END - mark end of function
@@ -86,7 +88,7 @@ symbol:		.frame	sp, framesize, rpc
 #define FEXPORT(symbol)					\
 		.globl	symbol;				\
 		.type	symbol, @function;		\
-symbol:
+symbol:		.insn
 
 /*
  * ABS - export absolute symbol