arch: arm: add armv6+ port

arch/arm/getcontext.S

@@ -0,0 +1,27 @@
+/*
+ * Copyright (c) 2018 William Pitcock <nenolod@dereferenced.org>
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * This software is provided 'as is' and without any warranty, express or
+ * implied.  In no event shall the authors be liable for any damages arising
+ * from the use of this software.
+ */
+
+.globl __getcontext;
+__getcontext:
+	/* copy all of the current registers into the ucontext structure */
+	add	r1, r0, #48
+	stmia	r1, {r4-r12}
+	str	r13, [r0,#84]
+	str	r14, [r0,#92]
+
+	/* return 0 */
+	mov	r0, #0
+	mov	pc, lr
+
+
+.weak getcontext;
+getcontext = __getcontext;

arch/arm/makecontext.c

@@ -0,0 +1,65 @@
+/*
+ * Copyright (c) 2018 William Pitcock <nenolod@dereferenced.org>
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * This software is provided 'as is' and without any warranty, express or
+ * implied.  In no event shall the authors be liable for any damages arising
+ * from the use of this software.
+ */
+
+#define _GNU_SOURCE
+#include <stddef.h>
+#include <stdarg.h>
+#include <signal.h>
+#include <string.h>
+#include <stdint.h>
+#include <stdio.h>
+
+
+extern void __start_context(void);
+
+
+void
+__makecontext(ucontext_t *ucp, void (*func)(void), int argc, ...)
+{
+	unsigned long *sp;
+	unsigned long *regp;
+	va_list va;
+	int i;
+
+	sp = (unsigned long *) ((uintptr_t) ucp->uc_stack.ss_sp + ucp->uc_stack.ss_size);
+	sp = (unsigned long *) (((uintptr_t) sp & -16L) - 8);
+
+	if (argc > 4)
+		sp -= (argc - 4);
+
+	ucp->uc_mcontext.arm_sp = (uintptr_t) sp;
+	ucp->uc_mcontext.arm_pc = (uintptr_t) func;
+	ucp->uc_mcontext.arm_r4 = (uintptr_t) ucp->uc_link;
+	ucp->uc_mcontext.arm_lr = (uintptr_t) &__start_context;
+
+	va_start(va, argc);
+
+	regp = &(ucp->uc_mcontext.arm_r0);
+
+	for (i = 0; (i < argc && i < 4); i++)
+		*regp++ = va_arg (va, unsigned long);
+
+	for (; i < argc; i++)
+		*sp++ = va_arg (va, unsigned long);
+
+	va_end(va);
+
+/*
+	printf("R4 offset = %d\n", offsetof(ucontext_t, uc_mcontext.arm_r4));
+	printf("SP offset = %d\n", offsetof(ucontext_t, uc_mcontext.arm_sp));
+	printf("LR offset = %d\n", offsetof(ucontext_t, uc_mcontext.arm_lr));
+	printf("PC offset = %d\n", offsetof(ucontext_t, uc_mcontext.arm_pc));
+ */
+}
+
+
+extern __typeof(__makecontext) makecontext __attribute__((weak, __alias__("__makecontext")));

arch/arm/setcontext.S

@@ -0,0 +1,26 @@
+/*
+ * Copyright (c) 2018 William Pitcock <nenolod@dereferenced.org>
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * This software is provided 'as is' and without any warranty, express or
+ * implied.  In no event shall the authors be liable for any damages arising
+ * from the use of this software.
+ */
+
+.globl __setcontext;
+__setcontext:
+	/* copy all of the current registers into the ucontext structure */
+	add	r14, r0, #32
+	ldmia	r14, {r0-r12}
+	ldr	r13, [r14, #52]
+	add	r14, r14, #56
+
+	/* load link register and jump to new context */
+	ldmia	r14, {r14, pc}
+
+
+.weak setcontext;
+setcontext = __setcontext;

arch/arm/startcontext.S

@@ -0,0 +1,23 @@
+/*
+ * Copyright (c) 2018 William Pitcock <nenolod@dereferenced.org>
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * This software is provided 'as is' and without any warranty, express or
+ * implied.  In no event shall the authors be liable for any damages arising
+ * from the use of this software.
+ */
+
+.globl __start_context;
+.fnstart
+.cantunwind
+	nop
+__start_context:
+	/* get the proper context into position and test for NULL */
+	movs	r0, r4
+	bne	__setcontext@plt
+
+	/* we are returning into a null context, it seems, so maybe we should exit */
+	b	exit@plt

arch/arm/swapcontext.S

@@ -0,0 +1,30 @@
+/*
+ * Copyright (c) 2018 William Pitcock <nenolod@dereferenced.org>
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * This software is provided 'as is' and without any warranty, express or
+ * implied.  In no event shall the authors be liable for any damages arising
+ * from the use of this software.
+ */
+
+.globl __swapcontext;
+__swapcontext:
+	/* copy all of the current registers into the ucontext structure */
+	add	r2, r0, #32
+	stmia	r2, {r0-r12}
+	str	r13, [r0,#84]
+	str	r14, [r0,#92]
+
+	/* load new registers from the second ucontext structure */
+	add	r14, r1, #32
+	ldmia	r14, {r0-r12}
+	ldr	r13, [r14, #52]
+	add	r14, r14, #56
+	ldmia	r14, {r14, pc}
+
+
+.weak swapcontext;
+swapcontext = __swapcontext;