MIPS: ELF: Set FP mode according to .MIPS.abiflags

This patch reads the .MIPS.abiflags section when it is present, and sets
the FP mode of the task accordingly. Any loaded ELF files which do not
contain a .MIPS.abiflags section will continue to observe the previous
behaviour, that is FR=1 if EF_MIPS_FP64 is set else FR=0.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/7681/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

2 files changed, 177 insertions, 3 deletions

diff --git a/arch/mips/kernel/Makefile b/arch/mips/kernel/Makefile
index 3982e5138f61..0945d804ec3a 100644
--- a/arch/mips/kernel/Makefile
+++ b/arch/mips/kernel/Makefile
@@ -4,9 +4,10 @@
 
 extra-y		:= head.o vmlinux.lds
 
-obj-y		+= cpu-probe.o branch.o entry.o genex.o idle.o irq.o process.o \
-		   prom.o ptrace.o reset.o setup.o signal.o syscall.o \
-		   time.o topology.o traps.o unaligned.o watch.o vdso.o
+obj-y		+= cpu-probe.o branch.o elf.o entry.o genex.o idle.o irq.o \
+		   process.o prom.o ptrace.o reset.o setup.o signal.o \
+		   syscall.o time.o topology.o traps.o unaligned.o watch.o \
+		   vdso.o
 
 ifdef CONFIG_FUNCTION_TRACER
 CFLAGS_REMOVE_ftrace.o = -pg
diff --git a/arch/mips/kernel/elf.c b/arch/mips/kernel/elf.c
new file mode 100644
index 000000000000..0933e0726f64
--- /dev/null
+++ b/arch/mips/kernel/elf.c
@@ -0,0 +1,173 @@
+/*
+ * Copyright (C) 2014 Imagination Technologies
+ * Author: Paul Burton <paul.burton@imgtec.com>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the
+ * Free Software Foundation;  either version 2 of the  License, or (at your
+ * option) any later version.
+ */
+
+#include <linux/elf.h>
+#include <linux/sched.h>
+
+enum {
+	FP_ERROR = -1,
+	FP_DOUBLE_64A = -2,
+};
+
+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 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;
+
+	ret = kernel_read(elf, phdr->p_offset, (char *)&abiflags,
+			  sizeof(abiflags));
+	if (ret < 0)
+		return ret;
+	if (ret != sizeof(abiflags))
+		return -EIO;
+
+	/* Record the required FP ABIs for use by mips_check_elf */
+	if (is_interp)
+		state->interp_fp_abi = abiflags.fp_abi;
+	else
+		state->fp_abi = abiflags.fp_abi;
+
+	return 0;
+}
+
+static inline unsigned get_fp_abi(struct elfhdr *ehdr, int in_abi)
+{
+	/* If the ABI requirement is provided, simply return that */
+	if (in_abi != -1)
+		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;
+}
+
+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;
+
+	/* Ignore non-O32 binaries */
+	if (config_enabled(CONFIG_64BIT) &&
+	    (ehdr->e_ident[EI_CLASS] != ELFCLASS32))
+		return 0;
+
+	fp_abi = get_fp_abi(ehdr, state->fp_abi);
+
+	if (has_interpreter) {
+		interp_fp_abi = get_fp_abi(ehdr, state->interp_fp_abi);
+
+		abi0 = min(fp_abi, interp_fp_abi);
+		abi1 = max(fp_abi, interp_fp_abi);
+	} else {
+		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;
+	}
+
+	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;
+
+	case FP_ERROR:
+		return -ELIBBAD;
+	}
+
+	return 0;
+}
+
+void mips_set_personality_fp(struct arch_elf_state *state)
+{
+	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);
+		clear_thread_flag(TIF_HYBRID_FPREGS);
+		break;
+
+	case FP_DOUBLE_64A:
+		/* FR=1, FRE=1 */
+		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;
+
+	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);
+
+		clear_thread_flag(TIF_HYBRID_FPREGS);
+		break;
+
+	default:
+	case FP_ERROR:
+		BUG();
+	}
+}