3 files changed, 194 insertions, 132 deletions

diff --git a/arch/mips/Kconfig.debug b/arch/mips/Kconfig.debug
index 88a9f433f6fc..3a2b775e8458 100644
--- a/arch/mips/Kconfig.debug
+++ b/arch/mips/Kconfig.debug
@@ -122,17 +122,4 @@ config SPINLOCK_TEST
 	help
 	  Add several files to the debugfs to test spinlock speed.
 
-config FP32XX_HYBRID_FPRS
-	bool "Run FP32 & FPXX code with hybrid FPRs"
-	depends on MIPS_O32_FP64_SUPPORT
-	help
-	  The hybrid FPR scheme is normally used only when a program needs to
-	  execute a mix of FP32 & FP64A code, since the trapping & emulation
-	  that it entails is expensive. When enabled, this option will lead
-	  to the kernel running programs which use the FP32 & FPXX FP ABIs
-	  using the hybrid FPR scheme, which can be useful for debugging
-	  purposes.
-
-	  If unsure, say N.
-
 endmenu
diff --git a/arch/mips/include/asm/elf.h b/arch/mips/include/asm/elf.h
index eb4d95de619c..535f196ffe02 100644
--- a/arch/mips/include/asm/elf.h
+++ b/arch/mips/include/asm/elf.h
@@ -417,13 +417,15 @@ extern unsigned long arch_randomize_brk(struct mm_struct *mm);
 struct arch_elf_state {
 	int fp_abi;
 	int interp_fp_abi;
-	int overall_abi;
+	int overall_fp_mode;
 };
 
+#define MIPS_ABI_FP_UNKNOWN	(-1)	/* Unknown FP ABI (kernel internal) */
+
 #define INIT_ARCH_ELF_STATE {			\
-	.fp_abi = -1,				\
-	.interp_fp_abi = -1,			\
-	.overall_abi = -1,			\
+	.fp_abi = MIPS_ABI_FP_UNKNOWN,		\
+	.interp_fp_abi = MIPS_ABI_FP_UNKNOWN,	\
+	.overall_fp_mode = -1,			\
 }
 
 extern int arch_elf_pt_proc(void *ehdr, void *phdr, struct file *elf,
diff --git a/arch/mips/kernel/elf.c b/arch/mips/kernel/elf.c
index c92b15df6893..d2c09f6475c5 100644
--- a/arch/mips/kernel/elf.c
+++ b/arch/mips/kernel/elf.c
@@ -11,29 +11,112 @@
 #include <linux/elf.h>
 #include <linux/sched.h>
 
+/* FPU modes */
 enum {
-	FP_ERROR = -1,
-	FP_DOUBLE_64A = -2,
+	FP_FRE,
+	FP_FR0,
+	FP_FR1,
 };
 
+/**
+ * struct mode_req - ABI FPU mode requirements
+ * @single:	The program being loaded needs an FPU but it will only issue
+ *		single precision instructions meaning that it can execute in
+ *		either FR0 or FR1.
+ * @soft:	The soft(-float) requirement means that the program being
+ *		loaded needs has no FPU dependency at all (i.e. it has no
+ *		FPU instructions).
+ * @fr1:	The program being loaded depends on FPU being in FR=1 mode.
+ * @frdefault:	The program being loaded depends on the default FPU mode.
+ *		That is FR0 for O32 and FR1 for N32/N64.
+ * @fre:	The program being loaded depends on FPU with FRE=1. This mode is
+ *		a bridge which uses FR=1 whilst still being able to maintain
+ *		full compatibility with pre-existing code using the O32 FP32
+ *		ABI.
+ *
+ * More information about the FP ABIs can be found here:
+ *
+ * https://dmz-portal.mips.com/wiki/MIPS_O32_ABI_-_FR0_and_FR1_Interlinking#10.4.1._Basic_mode_set-up
+ *
+ */
+
+struct mode_req {
+	bool single;
+	bool soft;
+	bool fr1;
+	bool frdefault;
+	bool fre;
+};
+
+static const struct mode_req fpu_reqs[] = {
+	[MIPS_ABI_FP_ANY]    = { true,  true,  true,  true,  true  },
+	[MIPS_ABI_FP_DOUBLE] = { false, false, false, true,  true  },
+	[MIPS_ABI_FP_SINGLE] = { true,  false, false, false, false },
+	[MIPS_ABI_FP_SOFT]   = { false, true,  false, false, false },
+	[MIPS_ABI_FP_OLD_64] = { false, false, false, false, false },
+	[MIPS_ABI_FP_XX]     = { false, false, true,  true,  true  },
+	[MIPS_ABI_FP_64]     = { false, false, true,  false, false },
+	[MIPS_ABI_FP_64A]    = { false, false, true,  false, true  }
+};
+
+/*
+ * Mode requirements when .MIPS.abiflags is not present in the ELF.
+ * Not present means that everything is acceptable except FR1.
+ */
+static struct mode_req none_req = { true, true, false, true, true };
+
 int arch_elf_pt_proc(void *_ehdr, void *_phdr, struct file *elf,
 		     bool is_interp, struct arch_elf_state *state)
 {
-	struct elfhdr *ehdr = _ehdr;
-	struct elf_phdr *phdr = _phdr;
+	struct elf32_hdr *ehdr32 = _ehdr;
+	struct elf32_phdr *phdr32 = _phdr;
+	struct elf64_phdr *phdr64 = _phdr;
 	struct mips_elf_abiflags_v0 abiflags;
 	int ret;
 
-	if (config_enabled(CONFIG_64BIT) &&
-	    (ehdr->e_ident[EI_CLASS] != ELFCLASS32))
-		return 0;
-	if (phdr->p_type != PT_MIPS_ABIFLAGS)
-		return 0;
-	if (phdr->p_filesz < sizeof(abiflags))
-		return -EINVAL;
+	/* Lets see if this is an O32 ELF */
+	if (ehdr32->e_ident[EI_CLASS] == ELFCLASS32) {
+		/* FR = 1 for N32 */
+		if (ehdr32->e_flags & EF_MIPS_ABI2)
+			state->overall_fp_mode = FP_FR1;
+		else
+			/* Set a good default FPU mode for O32 */
+			state->overall_fp_mode = cpu_has_mips_r6 ?
+				FP_FRE : FP_FR0;
+
+		if (ehdr32->e_flags & EF_MIPS_FP64) {
+			/*
+			 * Set MIPS_ABI_FP_OLD_64 for EF_MIPS_FP64. We will override it
+			 * later if needed
+			 */
+			if (is_interp)
+				state->interp_fp_abi = MIPS_ABI_FP_OLD_64;
+			else
+				state->fp_abi = MIPS_ABI_FP_OLD_64;
+		}
+		if (phdr32->p_type != PT_MIPS_ABIFLAGS)
+			return 0;
+
+		if (phdr32->p_filesz < sizeof(abiflags))
+			return -EINVAL;
+
+		ret = kernel_read(elf, phdr32->p_offset,
+				  (char *)&abiflags,
+				  sizeof(abiflags));
+	} else {
+		/* FR=1 is really the only option for 64-bit */
+		state->overall_fp_mode = FP_FR1;
+
+		if (phdr64->p_type != PT_MIPS_ABIFLAGS)
+			return 0;
+		if (phdr64->p_filesz < sizeof(abiflags))
+			return -EINVAL;
+
+		ret = kernel_read(elf, phdr64->p_offset,
+				  (char *)&abiflags,
+				  sizeof(abiflags));
+	}
 
-	ret = kernel_read(elf, phdr->p_offset, (char *)&abiflags,
-			  sizeof(abiflags));
 	if (ret < 0)
 		return ret;
 	if (ret != sizeof(abiflags))
@@ -48,35 +131,30 @@ int arch_elf_pt_proc(void *_ehdr, void *_phdr, struct file *elf,
 	return 0;
 }
 
-static inline unsigned get_fp_abi(struct elfhdr *ehdr, int in_abi)
+static inline unsigned get_fp_abi(int in_abi)
 {
 	/* If the ABI requirement is provided, simply return that */
-	if (in_abi != -1)
+	if (in_abi != MIPS_ABI_FP_UNKNOWN)
 		return in_abi;
 
-	/* If the EF_MIPS_FP64 flag was set, return MIPS_ABI_FP_64 */
-	if (ehdr->e_flags & EF_MIPS_FP64)
-		return MIPS_ABI_FP_64;
-
-	/* Default to MIPS_ABI_FP_DOUBLE */
-	return MIPS_ABI_FP_DOUBLE;
+	/* Unknown ABI */
+	return MIPS_ABI_FP_UNKNOWN;
 }
 
 int arch_check_elf(void *_ehdr, bool has_interpreter,
 		   struct arch_elf_state *state)
 {
-	struct elfhdr *ehdr = _ehdr;
-	unsigned fp_abi, interp_fp_abi, abi0, abi1;
+	struct elf32_hdr *ehdr = _ehdr;
+	struct mode_req prog_req, interp_req;
+	int fp_abi, interp_fp_abi, abi0, abi1, max_abi;
 
-	/* Ignore non-O32 binaries */
-	if (config_enabled(CONFIG_64BIT) &&
-	    (ehdr->e_ident[EI_CLASS] != ELFCLASS32))
+	if (!config_enabled(CONFIG_MIPS_O32_FP64_SUPPORT))
 		return 0;
 
-	fp_abi = get_fp_abi(ehdr, state->fp_abi);
+	fp_abi = get_fp_abi(state->fp_abi);
 
 	if (has_interpreter) {
-		interp_fp_abi = get_fp_abi(ehdr, state->interp_fp_abi);
+		interp_fp_abi = get_fp_abi(state->interp_fp_abi);
 
 		abi0 = min(fp_abi, interp_fp_abi);
 		abi1 = max(fp_abi, interp_fp_abi);
@@ -84,108 +162,103 @@ int arch_check_elf(void *_ehdr, bool has_interpreter,
 		abi0 = abi1 = fp_abi;
 	}
 
-	state->overall_abi = FP_ERROR;
-
-	if (abi0 == abi1) {
-		state->overall_abi = abi0;
-	} else if (abi0 == MIPS_ABI_FP_ANY) {
-		state->overall_abi = abi1;
-	} else if (abi0 == MIPS_ABI_FP_DOUBLE) {
-		switch (abi1) {
-		case MIPS_ABI_FP_XX:
-			state->overall_abi = MIPS_ABI_FP_DOUBLE;
-			break;
-
-		case MIPS_ABI_FP_64A:
-			state->overall_abi = FP_DOUBLE_64A;
-			break;
-		}
-	} else if (abi0 == MIPS_ABI_FP_SINGLE ||
-		   abi0 == MIPS_ABI_FP_SOFT) {
-		/* Cannot link with other ABIs */
-	} else if (abi0 == MIPS_ABI_FP_OLD_64) {
-		switch (abi1) {
-		case MIPS_ABI_FP_XX:
-		case MIPS_ABI_FP_64:
-		case MIPS_ABI_FP_64A:
-			state->overall_abi = MIPS_ABI_FP_64;
-			break;
-		}
-	} else if (abi0 == MIPS_ABI_FP_XX ||
-		   abi0 == MIPS_ABI_FP_64 ||
-		   abi0 == MIPS_ABI_FP_64A) {
-		state->overall_abi = MIPS_ABI_FP_64;
-	}
+	/* ABI limits. O32 = FP_64A, N32/N64 = FP_SOFT */
+	max_abi = ((ehdr->e_ident[EI_CLASS] == ELFCLASS32) &&
+		   (!(ehdr->e_flags & EF_MIPS_ABI2))) ?
+		MIPS_ABI_FP_64A : MIPS_ABI_FP_SOFT;
 
-	switch (state->overall_abi) {
-	case MIPS_ABI_FP_64:
-	case MIPS_ABI_FP_64A:
-	case FP_DOUBLE_64A:
-		if (!config_enabled(CONFIG_MIPS_O32_FP64_SUPPORT))
-			return -ELIBBAD;
-		break;
+	if ((abi0 > max_abi && abi0 != MIPS_ABI_FP_UNKNOWN) ||
+	    (abi1 > max_abi && abi1 != MIPS_ABI_FP_UNKNOWN))
+		return -ELIBBAD;
+
+	/* It's time to determine the FPU mode requirements */
+	prog_req = (abi0 == MIPS_ABI_FP_UNKNOWN) ? none_req : fpu_reqs[abi0];
+	interp_req = (abi1 == MIPS_ABI_FP_UNKNOWN) ? none_req : fpu_reqs[abi1];
 
-	case FP_ERROR:
+	/*
+	 * Check whether the program's and interp's ABIs have a matching FPU
+	 * mode requirement.
+	 */
+	prog_req.single = interp_req.single && prog_req.single;
+	prog_req.soft = interp_req.soft && prog_req.soft;
+	prog_req.fr1 = interp_req.fr1 && prog_req.fr1;
+	prog_req.frdefault = interp_req.frdefault && prog_req.frdefault;
+	prog_req.fre = interp_req.fre && prog_req.fre;
+
+	/*
+	 * Determine the desired FPU mode
+	 *
+	 * Decision making:
+	 *
+	 * - We want FR_FRE if FRE=1 and both FR=1 and FR=0 are false. This
+	 *   means that we have a combination of program and interpreter
+	 *   that inherently require the hybrid FP mode.
+	 * - If FR1 and FRDEFAULT is true, that means we hit the any-abi or
+	 *   fpxx case. This is because, in any-ABI (or no-ABI) we have no FPU
+	 *   instructions so we don't care about the mode. We will simply use
+	 *   the one preferred by the hardware. In fpxx case, that ABI can
+	 *   handle both FR=1 and FR=0, so, again, we simply choose the one
+	 *   preferred by the hardware. Next, if we only use single-precision
+	 *   FPU instructions, and the default ABI FPU mode is not good
+	 *   (ie single + any ABI combination), we set again the FPU mode to the
+	 *   one is preferred by the hardware. Next, if we know that the code
+	 *   will only use single-precision instructions, shown by single being
+	 *   true but frdefault being false, then we again set the FPU mode to
+	 *   the one that is preferred by the hardware.
+	 * - We want FP_FR1 if that's the only matching mode and the default one
+	 *   is not good.
+	 * - Return with -ELIBADD if we can't find a matching FPU mode.
+	 */
+	if (prog_req.fre && !prog_req.frdefault && !prog_req.fr1)
+		state->overall_fp_mode = FP_FRE;
+	else if ((prog_req.fr1 && prog_req.frdefault) ||
+		 (prog_req.single && !prog_req.frdefault))
+		/* Make sure 64-bit MIPS III/IV/64R1 will not pick FR1 */
+		state->overall_fp_mode = ((current_cpu_data.fpu_id & MIPS_FPIR_F64) &&
+					  cpu_has_mips_r2_r6) ?
+					  FP_FR1 : FP_FR0;
+	else if (prog_req.fr1)
+		state->overall_fp_mode = FP_FR1;
+	else  if (!prog_req.fre && !prog_req.frdefault &&
+		  !prog_req.fr1 && !prog_req.single && !prog_req.soft)
 		return -ELIBBAD;
-	}
 
 	return 0;
 }
 
-void mips_set_personality_fp(struct arch_elf_state *state)
+static inline void set_thread_fp_mode(int hybrid, int regs32)
 {
-	if (config_enabled(CONFIG_FP32XX_HYBRID_FPRS)) {
-		/*
-		 * Use hybrid FPRs for all code which can correctly execute
-		 * with that mode.
-		 */
-		switch (state->overall_abi) {
-		case MIPS_ABI_FP_DOUBLE:
-		case MIPS_ABI_FP_SINGLE:
-		case MIPS_ABI_FP_SOFT:
-		case MIPS_ABI_FP_XX:
-		case MIPS_ABI_FP_ANY:
-			/* FR=1, FRE=1 */
-			clear_thread_flag(TIF_32BIT_FPREGS);
-			set_thread_flag(TIF_HYBRID_FPREGS);
-			return;
-		}
-	}
-
-	switch (state->overall_abi) {
-	case MIPS_ABI_FP_DOUBLE:
-	case MIPS_ABI_FP_SINGLE:
-	case MIPS_ABI_FP_SOFT:
-		/* FR=0 */
-		set_thread_flag(TIF_32BIT_FPREGS);
+	if (hybrid)
+		set_thread_flag(TIF_HYBRID_FPREGS);
+	else
 		clear_thread_flag(TIF_HYBRID_FPREGS);
-		break;
-
-	case FP_DOUBLE_64A:
-		/* FR=1, FRE=1 */
+	if (regs32)
+		set_thread_flag(TIF_32BIT_FPREGS);
+	else
 		clear_thread_flag(TIF_32BIT_FPREGS);
-		set_thread_flag(TIF_HYBRID_FPREGS);
-		break;
+}
 
-	case MIPS_ABI_FP_64:
-	case MIPS_ABI_FP_64A:
-		/* FR=1, FRE=0 */
-		clear_thread_flag(TIF_32BIT_FPREGS);
-		clear_thread_flag(TIF_HYBRID_FPREGS);
-		break;
+void mips_set_personality_fp(struct arch_elf_state *state)
+{
+	/*
+	 * This function is only ever called for O32 ELFs so we should
+	 * not be worried about N32/N64 binaries.
+	 */
 
-	case MIPS_ABI_FP_XX:
-	case MIPS_ABI_FP_ANY:
-		if (!config_enabled(CONFIG_MIPS_O32_FP64_SUPPORT))
-			set_thread_flag(TIF_32BIT_FPREGS);
-		else
-			clear_thread_flag(TIF_32BIT_FPREGS);
+	if (!config_enabled(CONFIG_MIPS_O32_FP64_SUPPORT))
+		return;
 
-		clear_thread_flag(TIF_HYBRID_FPREGS);
+	switch (state->overall_fp_mode) {
+	case FP_FRE:
+		set_thread_fp_mode(1, 0);
+		break;
+	case FP_FR0:
+		set_thread_fp_mode(0, 1);
+		break;
+	case FP_FR1:
+		set_thread_fp_mode(0, 0);
 		break;
-
 	default:
-	case FP_ERROR:
 		BUG();
 	}
 }