add support for mips and mips64 r6 isa

mips32r6 and mips64r6 are actually new isas at both the asm source and
opcode levels (pre-r6 code cannot run on r6) and thus need to be
treated as a new subarch. the following changes are made, some of
which yield code generation improvements for non-r6 targets too:

- add subarch logic in configure script and reloc.h files for dynamic
  linker name.

- suppress use of .set mips2 asm directives (used to allow mips2
  atomic instructions on baseline mips1 builds; the kernel has to
  emulate them on mips1) except when actually needed. they cause wrong
  instruction encodings on r6, and pessimize inlining on at least some
  compilers.

- only hard-code sync instruction encoding on mips1.

- use "ZC" constraint instead of "m" constraint for llsc memory
  operands on r6, where the ll/sc instructions no longer accept full
  16-bit offsets.

- only hard-code rdhwr instruction encoding with .word on targets
  (pre-r2) where it may need trap-and-emulate by the kernel.
  otherwise, just use the instruction mnemonic, and allow an arbitrary
  destination register to be used.

arch/mips/atomic_arch.h

+#if __mips_isa_rev < 6
+#define LLSC_M "m"
+#else
+#define LLSC_M "ZC"
+#endif
+
 #define a_ll a_ll
 static inline int a_ll(volatile int *p)
 {
 	int v;
+#if __mips < 2
 	__asm__ __volatile__ (
 		".set push ; .set mips2\n\t"
 		"ll %0, %1"
 		"\n\t.set pop"
 		: "=r"(v) : "m"(*p));
+#else
+	__asm__ __volatile__ (
+		"ll %0, %1"
+		: "=r"(v) : LLSC_M(*p));
+#endif
 	return v;
 }
 
@@ -14,26 +26,33 @@ static inline int a_ll(volatile int *p)
 static inline int a_sc(volatile int *p, int v)
 {
 	int r;
+#if __mips < 2
 	__asm__ __volatile__ (
 		".set push ; .set mips2\n\t"
 		"sc %0, %1"
 		"\n\t.set pop"
 		: "=r"(r), "=m"(*p) : "0"(v) : "memory");
+#else
+	__asm__ __volatile__ (
+		"sc %0, %1"
+		: "=r"(r), "="LLSC_M(*p) : "0"(v) : "memory");
+#endif
 	return r;
 }
 
 #define a_barrier a_barrier
 static inline void a_barrier()
 {
+#if __mips < 2
 	/* mips2 sync, but using too many directives causes
 	 * gcc not to inline it, so encode with .long instead. */
 	__asm__ __volatile__ (".long 0xf" : : : "memory");
-#if 0
-	__asm__ __volatile__ (
-		".set push ; .set mips2 ; sync ; .set pop"
-		: : : "memory");
+#else
+	__asm__ __volatile__ ("sync" : : : "memory");
 #endif
 }
 
 #define a_pre_llsc a_barrier
 #define a_post_llsc a_barrier
+
+#undef LLSC_M

arch/mips/pthread_arch.h

 static inline struct pthread *__pthread_self()
 {
-#ifdef __clang__
-	char *tp;
-	__asm__ __volatile__ (".word 0x7c03e83b ; move %0, $3" : "=r" (tp) : : "$3" );
-#else
+#if __mips_isa_rev < 2
 	register char *tp __asm__("$3");
-	/* rdhwr $3,$29 */
 	__asm__ __volatile__ (".word 0x7c03e83b" : "=r" (tp) );
+#else
+	char *tp;
+	__asm__ __volatile__ ("rdhwr %0, $29" : "=r" (tp) );
 #endif
 	return (pthread_t)(tp - 0x7000 - sizeof(struct pthread));
 }

arch/mips/reloc.h

 #include <endian.h>
 
+#if __mips_isa_rev >= 6
+#define ISA_SUFFIX "r6"
+#else
+#define ISA_SUFFIX ""
+#endif
+
 #if __BYTE_ORDER == __LITTLE_ENDIAN
 #define ENDIAN_SUFFIX "el"
 #else
@@ -12,7 +18,7 @@
 #define FP_SUFFIX ""
 #endif
 
-#define LDSO_ARCH "mips" ENDIAN_SUFFIX FP_SUFFIX
+#define LDSO_ARCH "mips" ISA_SUFFIX ENDIAN_SUFFIX FP_SUFFIX
 
 #define TPOFF_K (-0x7000)
 

arch/mips64/atomic_arch.h

+#if __mips_isa_rev < 6
+#define LLSC_M "m"
+#else
+#define LLSC_M "ZC"
+#endif
+
 #define a_ll a_ll
 static inline int a_ll(volatile int *p)
 {
 	int v;
 	__asm__ __volatile__ (
 		"ll %0, %1"
-		: "=r"(v) : "m"(*p));
+		: "=r"(v) : LLSC_M(*p));
 	return v;
 }
 
@@ -14,7 +20,7 @@ static inline int a_sc(volatile int *p, int v)
 	int r;
 	__asm__ __volatile__ (
 		"sc %0, %1"
-		: "=r"(r), "=m"(*p) : "0"(v) : "memory");
+		: "=r"(r), "="LLSC_M(*p) : "0"(v) : "memory");
 	return r;
 }
 
@@ -24,7 +30,7 @@ static inline void *a_ll_p(volatile void *p)
 	void *v;
 	__asm__ __volatile__ (
 		"lld %0, %1"
-		: "=r"(v) : "m"(*(void *volatile *)p));
+		: "=r"(v) : LLSC_M(*(void *volatile *)p));
 	return v;
 }
 
@@ -34,17 +40,17 @@ static inline int a_sc_p(volatile void *p, void *v)
 	long r;
 	__asm__ __volatile__ (
 		"scd %0, %1"
-		: "=r"(r), "=m"(*(void *volatile *)p) : "0"(v) : "memory");
+		: "=r"(r), "="LLSC_M(*(void *volatile *)p) : "0"(v) : "memory");
 	return r;
 }
 
 #define a_barrier a_barrier
 static inline void a_barrier()
 {
-	/* mips2 sync, but using too many directives causes
-	 * gcc not to inline it, so encode with .long instead. */
-	__asm__ __volatile__ (".long 0xf" : : : "memory");
+	__asm__ __volatile__ ("sync" : : : "memory");
 }
 
 #define a_pre_llsc a_barrier
 #define a_post_llsc a_barrier
+
+#undef LLSC_M

arch/mips64/pthread_arch.h

 static inline struct pthread *__pthread_self()
 {
-#ifdef __clang__
-	char *tp;
-	__asm__ __volatile__ (".word 0x7c03e83b ; move %0, $3" : "=r" (tp) : : "$3" );
-#else
+#if __mips_isa_rev < 2
 	register char *tp __asm__("$3");
 	__asm__ __volatile__ (".word 0x7c03e83b" : "=r" (tp) );
+#else
+	char *tp;
+	__asm__ __volatile__ ("rdhwr %0, $29" : "=r" (tp) );
 #endif
 	return (pthread_t)(tp - 0x7000 - sizeof(struct pthread));
 }

arch/mips64/reloc.h

@@ -4,6 +4,12 @@
 #define _GNU_SOURCE
 #include <endian.h>
 
+#if __mips_isa_rev >= 6
+#define ISA_SUFFIX "r6"
+#else
+#define ISA_SUFFIX ""
+#endif
+
 #if __BYTE_ORDER == __LITTLE_ENDIAN
 #define ENDIAN_SUFFIX "el"
 #else
@@ -16,7 +22,7 @@
 #define FP_SUFFIX ""
 #endif
 
-#define LDSO_ARCH "mips64" ENDIAN_SUFFIX FP_SUFFIX
+#define LDSO_ARCH "mips64" ISA_SUFFIX ENDIAN_SUFFIX FP_SUFFIX
 
 #define TPOFF_K (-0x7000)
 

configure

@@ -612,11 +612,13 @@ trycppif __AARCH64EB__ "$t" && SUBARCH=${SUBARCH}_be
 fi
 
 if test "$ARCH" = "mips" ; then
+trycppif "__mips_isa_rev >= 6" "$t" && SUBARCH=${SUBARCH}r6
 trycppif "_MIPSEL || __MIPSEL || __MIPSEL__" "$t" && SUBARCH=${SUBARCH}el
 trycppif __mips_soft_float "$t" && SUBARCH=${SUBARCH}-sf
 fi
 
 if test "$ARCH" = "mips64" ; then
+trycppif "__mips_isa_rev >= 6" "$t" && SUBARCH=${SUBARCH}r6
 trycppif "_MIPSEL || __MIPSEL || __MIPSEL__" "$t" && SUBARCH=${SUBARCH}el
 trycppif __mips_soft_float "$t" && SUBARCH=${SUBARCH}-sf
 fi