arm: Introduce setjmp/longjmp

To quit an EFI application we will need logic to jump to the caller
of a function without returning from the function we called into,
so we need setjmp/longjmp functionality.

This patch introduces a trivial implementation of these that I
verified works on armv7, thumb2 and aarch64.

Signed-off-by: Alexander Graf <agraf@suse.de>

arch/arm/include/asm/setjmp.h

+/*
+ * (C) Copyright 2016
+ * Alexander Graf <agraf@suse.de>
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#ifndef _SETJMP_H_
+#define _SETJMP_H_	1
+
+struct jmp_buf_data {
+	ulong target;
+	ulong regs[5];
+};
+
+typedef struct jmp_buf_data jmp_buf[1];
+
+static inline int setjmp(jmp_buf jmp)
+{
+	long r = 0;
+
+#ifdef CONFIG_ARM64
+	asm volatile(
+		"adr x1, jmp_target\n"
+		"str x1, %1\n"
+		"stp x26, x27, %2\n"
+		"stp x28, x29, %3\n"
+		"mov x1, sp\n"
+		"str x1, %4\n"
+		"b 2f\n"
+		"jmp_target: "
+		"mov %0, #1\n"
+		"2:\n"
+		: "+r" (r), "=m" (jmp->target),
+		  "=m" (jmp->regs[0]), "=m" (jmp->regs[2]),
+		  "=m" (jmp->regs[4])
+		:
+		: "x0", "x1", "x2", "x3", "x4", "x5", "x6", "x7",
+		  "x8", "x9", "x10", "x11", "x12", "x13", "x14", "x15",
+		  "x16", "x17", "x18", "x19", "x20", "x21", "x22",
+		  "x23", "x24", "x25", /* x26, x27, x28, x29, sp */
+		  "x30", "cc", "memory");
+#else
+	asm volatile(
+#ifdef CONFIG_SYS_THUMB_BUILD
+		"adr r0, jmp_target + 1\n"
+#else
+		"adr r0, jmp_target\n"
+#endif
+		"mov r1, %1\n"
+		"mov r2, sp\n"
+		"stm r1, {r0, r2, r4, r5, r6, r7}\n"
+		"b 2f\n"
+		"jmp_target: "
+		"mov %0, #1\n"
+		"2:\n"
+		: "+l" (r)
+		: "l" (&jmp->target)
+		: "r0", "r1", "r2", "r3", /* "r4", "r5", "r6", "r7", */
+		  "r8", "r9", "r10", "r11", /* sp, */ "ip", "lr",
+		  "cc", "memory");
+#endif
+
+printf("%s:%d target=%#lx\n", __func__, __LINE__, jmp->target);
+
+	return r;
+}
+
+static inline __noreturn void longjmp(jmp_buf jmp)
+{
+#ifdef CONFIG_ARM64
+	asm volatile(
+		"ldr x0, %0\n"
+		"ldr x1, %3\n"
+		"mov sp, x1\n"
+		"ldp x26, x27, %1\n"
+		"ldp x28, x25, %2\n"
+		"mov x29, x25\n"
+		"br x0\n"
+		:
+		: "m" (jmp->target), "m" (jmp->regs[0]), "m" (jmp->regs[2]),
+		  "m" (jmp->regs[4])
+		: "x0", "x1", "x25", "x26", "x27", "x28");
+#else
+	asm volatile(
+		"mov r1, %0\n"
+		"ldm r1, {r0, r2, r4, r5, r6, r7}\n"
+		"mov sp, r2\n"
+		"bx r0\n"
+		:
+		: "l" (&jmp->target)
+		: "r1");
+#endif
+
+	while (1) { }
+}
+
+
+#endif /* _SETJMP_H_ */