Merge tag 'mips_4.19_2' of git://git.kernel.org/pub/scm/linux/kernel/git/mips/linux

Pull MIPS fixes from Paul Burton:

  - Fix microMIPS build failures by adding a .insn directive to the
    barrier_before_unreachable() asm statement in order to convince the
    toolchain that the asm statement is a valid branch target rather
    than a bogus attempt to switch ISA.

  - Clean up our declarations of TLB functions that we overwrite with
    generated code in order to prevent the compiler making assumptions
    about alignment that cause microMIPS kernels built with GCC 7 &
    above to die early during boot.

  - Fix up a regression for MIPS32 kernels which slipped into the main
    MIPS pull for 4.19, causing CONFIG_32BIT=y kernels to contain
    inappropriate MIPS64 instructions.

  - Extend our existing workaround for MIPSr6 builds that end up using
    the __multi3 intrinsic to GCC 7 & below, rather than just GCC 7.

* tag 'mips_4.19_2' of git://git.kernel.org/pub/scm/linux/kernel/git/mips/linux:
  MIPS: lib: Provide MIPS64r6 __multi3() for GCC < 7
  MIPS: Workaround GCC __builtin_unreachable reordering bug
  compiler.h: Allow arch-specific asm/compiler.h
  MIPS: Avoid move psuedo-instruction whilst using MIPS_ISA_LEVEL
  MIPS: Consistently declare TLB functions
  MIPS: Export tlbmiss_handler_setup_pgd near its definition

arch/Kconfig

@@ -841,6 +841,14 @@ config REFCOUNT_FULL
 	  against various use-after-free conditions that can be used in
 	  security flaw exploits.
 
+config HAVE_ARCH_COMPILER_H
+	bool
+	help
+	  An architecture can select this if it provides an
+	  asm/compiler.h header that should be included after
+	  linux/compiler-*.h in order to override macro definitions that those
+	  headers generally provide.
+
 config HAVE_ARCH_PREL32_RELOCATIONS
 	bool
 	help

arch/mips/Kconfig

@@ -33,6 +33,7 @@ config MIPS
 	select GENERIC_SMP_IDLE_THREAD
 	select GENERIC_TIME_VSYSCALL
 	select HANDLE_DOMAIN_IRQ
+	select HAVE_ARCH_COMPILER_H
 	select HAVE_ARCH_JUMP_LABEL
 	select HAVE_ARCH_KGDB
 	select HAVE_ARCH_MMAP_RND_BITS if MMU

arch/mips/include/asm/asm-prototypes.h

@@ -5,3 +5,4 @@
 #include <asm-generic/asm-prototypes.h>
 #include <linux/uaccess.h>
 #include <asm/ftrace.h>
+#include <asm/mmu_context.h>

arch/mips/include/asm/atomic.h

@@ -122,8 +122,8 @@ static __inline__ int atomic_fetch_##op##_relaxed(int i, atomic_t * v)	      \
 		"	" #asm_op " %0, %1, %3				\n"   \
 		"	sc	%0, %2					\n"   \
 		"\t" __scbeqz "	%0, 1b					\n"   \
-		"	move	%0, %1					\n"   \
 		"	.set	mips0					\n"   \
+		"	move	%0, %1					\n"   \
 		: "=&r" (result), "=&r" (temp),				      \
 		  "+" GCC_OFF_SMALL_ASM() (v->counter)			      \
 		: "Ir" (i));						      \
@@ -190,9 +190,11 @@ static __inline__ int atomic_sub_if_positive(int i, atomic_t * v)
 		__asm__ __volatile__(
 		"	.set	"MIPS_ISA_LEVEL"			\n"
 		"1:	ll	%1, %2		# atomic_sub_if_positive\n"
+		"	.set	mips0					\n"
 		"	subu	%0, %1, %3				\n"
 		"	move	%1, %0					\n"
 		"	bltz	%0, 1f					\n"
+		"	.set	"MIPS_ISA_LEVEL"			\n"
 		"	sc	%1, %2					\n"
 		"\t" __scbeqz "	%1, 1b					\n"
 		"1:							\n"

arch/mips/include/asm/compiler.h

@@ -8,6 +8,41 @@
 #ifndef _ASM_COMPILER_H
 #define _ASM_COMPILER_H
 
+/*
+ * With GCC 4.5 onwards we can use __builtin_unreachable to indicate to the
+ * compiler that a particular code path will never be hit. This allows it to be
+ * optimised out of the generated binary.
+ *
+ * Unfortunately at least GCC 4.6.3 through 7.3.0 inclusive suffer from a bug
+ * that can lead to instructions from beyond an unreachable statement being
+ * incorrectly reordered into earlier delay slots if the unreachable statement
+ * is the only content of a case in a switch statement. This can lead to
+ * seemingly random behaviour, such as invalid memory accesses from incorrectly
+ * reordered loads or stores. See this potential GCC fix for details:
+ *
+ *   https://gcc.gnu.org/ml/gcc-patches/2015-09/msg00360.html
+ *
+ * It is unclear whether GCC 8 onwards suffer from the same issue - nothing
+ * relevant is mentioned in GCC 8 release notes and nothing obviously relevant
+ * stands out in GCC commit logs, but these newer GCC versions generate very
+ * different code for the testcase which doesn't exhibit the bug.
+ *
+ * GCC also handles stack allocation suboptimally when calling noreturn
+ * functions or calling __builtin_unreachable():
+ *
+ *   https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82365
+ *
+ * We work around both of these issues by placing a volatile asm statement,
+ * which GCC is prevented from reordering past, prior to __builtin_unreachable
+ * calls.
+ *
+ * The .insn statement is required to ensure that any branches to the
+ * statement, which sadly must be kept due to the asm statement, are known to
+ * be branches to code and satisfy linker requirements for microMIPS kernels.
+ */
+#undef barrier_before_unreachable
+#define barrier_before_unreachable() asm volatile(".insn")
+
 #if __GNUC__ > 3 || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4)
 #define GCC_IMM_ASM() "n"
 #define GCC_REG_ACCUM "$0"

arch/mips/include/asm/mmu_context.h

@@ -32,6 +32,7 @@ do {									\
 } while (0)
 
 extern void tlbmiss_handler_setup_pgd(unsigned long);
+extern char tlbmiss_handler_setup_pgd_end[];
 
 /* Note: This is also implemented with uasm in arch/mips/kvm/entry.c */
 #define TLBMISS_HANDLER_SETUP_PGD(pgd)					\

arch/mips/include/asm/tlbex.h

@@ -24,4 +24,13 @@ void build_tlb_write_entry(u32 **p, struct uasm_label **l,
 			   struct uasm_reloc **r,
 			   enum tlb_write_entry wmode);
 
+extern void handle_tlbl(void);
+extern char handle_tlbl_end[];
+
+extern void handle_tlbs(void);
+extern char handle_tlbs_end[];
+
+extern void handle_tlbm(void);
+extern char handle_tlbm_end[];
+
 #endif /* __ASM_TLBEX_H */

arch/mips/kernel/traps.c

@@ -67,14 +67,12 @@
 #include <asm/mmu_context.h>
 #include <asm/types.h>
 #include <asm/stacktrace.h>
+#include <asm/tlbex.h>
 #include <asm/uasm.h>
 
 extern void check_wait(void);
 extern asmlinkage void rollback_handle_int(void);
 extern asmlinkage void handle_int(void);
-extern u32 handle_tlbl[];
-extern u32 handle_tlbs[];
-extern u32 handle_tlbm[];
 extern asmlinkage void handle_adel(void);
 extern asmlinkage void handle_ades(void);
 extern asmlinkage void handle_ibe(void);

arch/mips/lib/multi3.c

@@ -4,12 +4,12 @@
 #include "libgcc.h"
 
 /*
- * GCC 7 suboptimally generates __multi3 calls for mips64r6, so for that
- * specific case only we'll implement it here.
+ * GCC 7 & older can suboptimally generate __multi3 calls for mips64r6, so for
+ * that specific case only we implement that intrinsic here.
  *
  * See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82981
  */
-#if defined(CONFIG_64BIT) && defined(CONFIG_CPU_MIPSR6) && (__GNUC__ == 7)
+#if defined(CONFIG_64BIT) && defined(CONFIG_CPU_MIPSR6) && (__GNUC__ < 8)
 
 /* multiply 64-bit values, low 64-bits returned */
 static inline long long notrace dmulu(long long a, long long b)

arch/mips/mm/tlb-funcs.S

@@ -12,16 +12,17 @@
  * Copyright (C) 2012  Ralf Baechle <ralf@linux-mips.org>
  */
 #include <asm/asm.h>
+#include <asm/export.h>
 #include <asm/regdef.h>
 
 #define FASTPATH_SIZE	128
 
-EXPORT(tlbmiss_handler_setup_pgd_start)
 LEAF(tlbmiss_handler_setup_pgd)
 1:	j	1b		/* Dummy, will be replaced. */
 	.space	64
 END(tlbmiss_handler_setup_pgd)
 EXPORT(tlbmiss_handler_setup_pgd_end)
+EXPORT_SYMBOL_GPL(tlbmiss_handler_setup_pgd)
 
 LEAF(handle_tlbm)
 	.space		FASTPATH_SIZE * 4

include/linux/compiler_types.h

@@ -66,6 +66,18 @@ extern void __chk_io_ptr(const volatile void __iomem *);
 #error "Unknown compiler"
 #endif
 
+/*
+ * Some architectures need to provide custom definitions of macros provided
+ * by linux/compiler-*.h, and can do so using asm/compiler.h. We include that
+ * conditionally rather than using an asm-generic wrapper in order to avoid
+ * build failures if any C compilation, which will include this file via an
+ * -include argument in c_flags, occurs prior to the asm-generic wrappers being
+ * generated.
+ */
+#ifdef CONFIG_HAVE_ARCH_COMPILER_H
+#include <asm/compiler.h>
+#endif
+
 /*
  * Generic compiler-independent macros required for kernel
  * build go below this comment. Actual compiler/compiler version