[PATCH v4 19/19] arm: vectors support

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Add support for tests to use exception handlers using
install_exception_handler(). This patch also adds phys_start_usr(),
which can be used to start a function in USR mode, using a stack
set up in a new memregion. phys_start_usr() is used by new selftest
tests that check the new vector support.

Signed-off-by: Andrew Jones <drjones@xxxxxxxxxx>
---
v4: a couple tweaks to fit changes in the other patches,
    vectors-usr test now has an 8K usr stack
v3:
  - squashed in 'arm: Simplify exceptions_init in cstart.S'
    [Christoffer Dall]
  - suggested function name changes and comment additions
    [Christoffer Dall]
  - fix a bug with stack restore from usr mode exceptions that
    Christoffer pointed out. Add a get_sp() accessor too.
---
 arm/cstart.S            | 174 ++++++++++++++++++++++++++++++++++++++++++++++++
 arm/flat.lds            |   7 +-
 arm/selftest.c          | 122 ++++++++++++++++++++++++++++++++-
 arm/unittests.cfg       |  12 ++++
 config/config-arm.mak   |   3 +-
 lib/arm/asm/processor.h |  40 +++++++++++
 lib/arm/processor.c     | 115 ++++++++++++++++++++++++++++++++
 lib/libcflat.h          |   3 +
 8 files changed, 473 insertions(+), 3 deletions(-)
 create mode 100644 lib/arm/asm/processor.h
 create mode 100644 lib/arm/processor.c

diff --git a/arm/cstart.S b/arm/cstart.S
index e28251db2950d..cc87ece4b6b40 100644
--- a/arm/cstart.S
+++ b/arm/cstart.S
@@ -5,6 +5,10 @@
  *
  * This work is licensed under the terms of the GNU LGPL, version 2.
  */
+#define __ASSEMBLY__
+#include "asm/asm-offsets.h"
+#include "asm/ptrace.h"
+#include "asm/cp15.h"
 
 .arm
 
@@ -17,6 +21,13 @@ start:
 	 * See the kernel doc Documentation/arm/Booting
 	 */
 	ldr	sp, =stacktop
+	push	{r0-r3}
+
+	/* set up vector table and mode stacks */
+	bl	exceptions_init
+
+	/* complete setup */
+	pop	{r0-r3}
 	bl	setup
 
 	/* run the test */
@@ -27,9 +38,172 @@ start:
 	bl	exit
 	b	halt
 
+
+.macro set_mode_stack mode, stack
+	add	\stack, #S_FRAME_SIZE
+	msr	cpsr_c, #(\mode | PSR_I_BIT | PSR_F_BIT)
+	mov	sp, \stack
+.endm
+
+exceptions_init:
+	mrc	p15, 0, r2, c1, c0, 0	@ read SCTLR
+	bic	r2, #CR_V		@ SCTLR.V := 0
+	mcr	p15, 0, r2, c1, c0, 0	@ write SCTLR
+	ldr	r2, =vector_table
+	mcr	p15, 0, r2, c12, c0, 0	@ write VBAR
+
+	mrs	r2, cpsr
+	ldr	r1, =exception_stacks
+
+	/* first frame reserved for svc mode */
+	set_mode_stack	UND_MODE, r1
+	set_mode_stack	ABT_MODE, r1
+	set_mode_stack	IRQ_MODE, r1
+	set_mode_stack	FIQ_MODE, r1
+
+	msr	cpsr_cxsf, r2		@ back to svc mode
+	mov	pc, lr
+
 .text
 
 .globl halt
 halt:
 1:	wfi
 	b	1b
+
+/*
+ * Vector stubs
+ * Simplified version of the Linux kernel implementation
+ *   arch/arm/kernel/entry-armv.S
+ *
+ * Each mode has an S_FRAME_SIZE sized stack initialized
+ * in exceptions_init
+ */
+.macro vector_stub, name, vec, mode, correction=0
+.align 5
+vector_\name:
+.if \correction
+	sub	lr, lr, #\correction
+.endif
+	/*
+	 * Save r0, r1, lr_<exception> (parent PC)
+	 * and spsr_<exception> (parent CPSR)
+	 */
+	str	r0, [sp, #S_R0]
+	str	r1, [sp, #S_R1]
+	str	lr, [sp, #S_PC]
+	mrs	r0, spsr
+	str	r0, [sp, #S_PSR]
+
+	/* Prepare for SVC32 mode. */
+	mrs	r0, cpsr
+	bic	r0, #MODE_MASK
+	orr	r0, #SVC_MODE
+	msr	spsr_cxsf, r0
+
+	/* Branch to handler in SVC mode */
+	mov	r0, #\vec
+	mov	r1, sp
+	ldr	lr, =vector_common
+	movs	pc, lr
+.endm
+
+vector_stub 	rst,	0, UND_MODE
+vector_stub	und,	1, UND_MODE
+vector_stub	pabt,	3, ABT_MODE, 4
+vector_stub	dabt,	4, ABT_MODE, 8
+vector_stub	irq,	6, IRQ_MODE, 4
+vector_stub	fiq,	7, FIQ_MODE, 4
+
+.align 5
+vector_svc:
+	/*
+	 * Save r0, r1, lr_<exception> (parent PC)
+	 * and spsr_<exception> (parent CPSR)
+	 */
+	push	{ r1 }
+	ldr	r1, =exception_stacks
+	str	r0, [r1, #S_R0]
+	pop	{ r0 }
+	str	r0, [r1, #S_R1]
+	str	lr, [r1, #S_PC]
+	mrs	r0, spsr
+	str	r0, [r1, #S_PSR]
+
+	/*
+	 * Branch to handler, still in SVC mode.
+	 * r0 := 2 is the svc vector number.
+	 */
+	mov	r0, #2
+	ldr	lr, =vector_common
+	mov	pc, lr
+
+vector_common:
+	/* make room for pt_regs */
+	sub	sp, #S_FRAME_SIZE
+	tst	sp, #4			@ check stack alignment
+	subne	sp, #4
+
+	/* store registers r0-r12 */
+	stmia	sp, { r0-r12 }		@ stored wrong r0 and r1, fix later
+
+	/* get registers saved in the stub */
+	ldr	r2, [r1, #S_R0]		@ r0
+	ldr	r3, [r1, #S_R1]		@ r1
+	ldr	r4, [r1, #S_PC] 	@ lr_<exception> (parent PC)
+	ldr	r5, [r1, #S_PSR]	@ spsr_<exception> (parent CPSR)
+
+	/* fix r0 and r1 */
+	str	r2, [sp, #S_R0]
+	str	r3, [sp, #S_R1]
+
+	/* store sp_svc, if we were in usr mode we'll fix this later */
+	add	r6, sp, #S_FRAME_SIZE
+	addne	r6, #4			@ stack wasn't aligned
+	str	r6, [sp, #S_SP]
+
+	str	lr, [sp, #S_LR]		@ store lr_svc, fix later for usr mode
+	str	r4, [sp, #S_PC]		@ store lr_<exception>
+	str	r5, [sp, #S_PSR]	@ store spsr_<exception>
+
+	/* set ORIG_r0 */
+	mov	r2, #-1
+	str	r2, [sp, #S_OLD_R0]
+
+	/* if we were in usr mode then we need sp_usr and lr_usr instead */
+	and	r1, r5, #MODE_MASK
+	cmp	r1, #USR_MODE
+	bne	1f
+	add	r1, sp, #S_SP
+	stmia	r1, { sp,lr }^
+
+	/* Call the handler. r0 is the vector number, r1 := pt_regs */
+1:	mov	r1, sp
+	bl	do_handle_exception
+
+	/*
+	 * make sure we restore sp_svc on mode change. No need to
+	 * worry about lr_svc though, as that gets clobbered on
+	 * exception entry anyway.
+	 */
+	str	r6, [sp, #S_SP]
+
+	/* return from exception */
+	msr	spsr_cxsf, r5
+	ldmia	sp, { r0-pc }^
+
+.align 5
+vector_addrexcptn:
+	b	vector_addrexcptn
+
+.section .text.ex
+.align 5
+vector_table:
+	b	vector_rst
+	b	vector_und
+	b	vector_svc
+	b	vector_pabt
+	b	vector_dabt
+	b	vector_addrexcptn	@ should never happen
+	b	vector_irq
+	b	vector_fiq
diff --git a/arm/flat.lds b/arm/flat.lds
index 3e5d72e24989b..ee9fc0ab79abc 100644
--- a/arm/flat.lds
+++ b/arm/flat.lds
@@ -3,7 +3,12 @@ SECTIONS
 {
     .text : { *(.init) *(.text) *(.text.*) }
     . = ALIGN(4K);
-    .data : { *(.data) }
+    .data : {
+        exception_stacks = .;
+        . += 4K;
+        exception_stacks_end = .;
+        *(.data)
+    }
     . = ALIGN(16);
     .rodata : { *(.rodata) }
     . = ALIGN(16);
diff --git a/arm/selftest.c b/arm/selftest.c
index 45729e9ac85d9..d8c9cae7e4ec1 100644
--- a/arm/selftest.c
+++ b/arm/selftest.c
@@ -7,6 +7,9 @@
  */
 #include "libcflat.h"
 #include "asm/setup.h"
+#include "asm/ptrace.h"
+#include "asm/asm-offsets.h"
+#include "asm/processor.h"
 
 #define TESTGRP "selftest"
 
@@ -74,14 +77,131 @@ static void check_setup(int argc, char **argv)
 	assert_args(nr_tests, 2);
 }
 
+static struct pt_regs expected_regs;
+/*
+ * Capture the current register state and execute an instruction
+ * that causes an exception. The test handler will check that its
+ * capture of the current register state matches the capture done
+ * here.
+ *
+ * NOTE: update clobber list if passed insns needs more than r0,r1
+ */
+#define test_exception(pre_insns, excptn_insn, post_insns)	\
+	asm volatile(						\
+		pre_insns "\n"					\
+		"mov	r0, %0\n"				\
+		"stmia	r0, { r0-lr }\n"			\
+		"mrs	r1, cpsr\n"				\
+		"str	r1, [r0, #" __stringify(S_PSR) "]\n"	\
+		"mov	r1, #-1\n"				\
+		"str	r1, [r0, #" __stringify(S_OLD_R0) "]\n"	\
+		"add	r1, pc, #8\n"				\
+		"str	r1, [r0, #" __stringify(S_R1) "]\n"	\
+		"str	r1, [r0, #" __stringify(S_PC) "]\n"	\
+		excptn_insn "\n"				\
+		post_insns "\n"					\
+	:: "r" (&expected_regs) : "r0", "r1")
+
+static bool check_regs(struct pt_regs *regs)
+{
+	unsigned i;
+
+	/* exception handlers should always run in svc mode */
+	if (current_mode() != SVC_MODE)
+		return false;
+
+	for (i = 0; i < ARRAY_SIZE(regs->uregs); ++i) {
+		if (regs->uregs[i] != expected_regs.uregs[i])
+			return false;
+	}
+
+	return true;
+}
+
+static bool und_works;
+static void und_handler(struct pt_regs *regs)
+{
+	und_works = check_regs(regs);
+}
+
+static bool check_und(void)
+{
+	install_exception_handler(EXCPTN_UND, und_handler);
+
+	/* issue an instruction to a coprocessor we don't have */
+	test_exception("", "mcr p2, 0, r0, c0, c0", "");
+
+	install_exception_handler(EXCPTN_UND, NULL);
+
+	return und_works;
+}
+
+static bool svc_works;
+static void svc_handler(struct pt_regs *regs)
+{
+	u32 svc = *(u32 *)(regs->ARM_pc - 4) & 0xffffff;
+
+	if (processor_mode(regs) == SVC_MODE) {
+		/*
+		 * When issuing an svc from supervisor mode lr_svc will
+		 * get corrupted. So before issuing the svc, callers must
+		 * always push it on the stack. We pushed it to offset 4.
+		 */
+		regs->ARM_lr = *(unsigned long *)(regs->ARM_sp + 4);
+	}
+
+	svc_works = check_regs(regs) && svc == 123;
+}
+
+static bool check_svc(void)
+{
+	install_exception_handler(EXCPTN_SVC, svc_handler);
+
+	if (current_mode() == SVC_MODE) {
+		/*
+		 * An svc from supervisor mode will corrupt lr_svc and
+		 * spsr_svc. We need to save/restore them separately.
+		 */
+		test_exception(
+			"mrs	r0, spsr\n"
+			"push	{ r0,lr }\n",
+			"svc	#123\n",
+			"pop	{ r0,lr }\n"
+			"msr	spsr_cxsf, r0\n"
+		);
+	} else {
+		test_exception("", "svc #123", "");
+	}
+
+	install_exception_handler(EXCPTN_SVC, NULL);
+
+	return svc_works;
+}
+
+static void check_vectors(void *arg __unused)
+{
+	report("%s", check_und() && check_svc(), testnam);
+	exit(report_summary());
+}
+
 int main(int argc, char **argv)
 {
 	assert_args(argc, 1);
 
 	testnam_set(argv[0]);
 
-	if (strcmp(argv[0], "setup") == 0)
+	if (strcmp(argv[0], "setup") == 0) {
+
 		check_setup(argc-1, &argv[1]);
 
+	} else if (strcmp(argv[0], "vectors-svc") == 0) {
+
+		check_vectors(NULL);
+
+	} else if (strcmp(argv[0], "vectors-usr") == 0) {
+
+		phys_start_usr(2*PAGE_SIZE, check_vectors, NULL);
+	}
+
 	return report_summary();
 }
diff --git a/arm/unittests.cfg b/arm/unittests.cfg
index da9dfd7b1f118..57f5f90f3e808 100644
--- a/arm/unittests.cfg
+++ b/arm/unittests.cfg
@@ -16,3 +16,15 @@ file = selftest.flat
 smp  = 1
 extra_params = -m 256 -append 'setup smp=1 mem=256'
 groups = selftest
+
+# Test vector setup and exception handling (svc mode).
+[selftest::vectors-svc]
+file = selftest.flat
+extra_params = -append 'vectors-svc'
+groups = selftest
+
+# Test vector setup and exception handling (usr mode).
+[selftest::vectors-usr]
+file = selftest.flat
+extra_params = -append 'vectors-usr'
+groups = selftest
diff --git a/config/config-arm.mak b/config/config-arm.mak
index ead191f4954f4..2a62b5847e230 100644
--- a/config/config-arm.mak
+++ b/config/config-arm.mak
@@ -39,7 +39,8 @@ cflatobjs += \
 	lib/virtio-testdev.o \
 	lib/arm/io.o \
 	lib/arm/setup.o \
-	lib/arm/spinlock.o
+	lib/arm/spinlock.o \
+	lib/arm/processor.o
 
 libeabi = lib/arm/libeabi.a
 eabiobjs = lib/arm/eabi_compat.o
diff --git a/lib/arm/asm/processor.h b/lib/arm/asm/processor.h
new file mode 100644
index 0000000000000..b7d3be00135fd
--- /dev/null
+++ b/lib/arm/asm/processor.h
@@ -0,0 +1,40 @@
+#ifndef _ASMARM_PROCESSOR_H_
+#define _ASMARM_PROCESSOR_H_
+/*
+ * Copyright (C) 2014, Red Hat Inc, Andrew Jones <drjones@xxxxxxxxxx>
+ *
+ * This work is licensed under the terms of the GNU LGPL, version 2.
+ */
+#include "ptrace.h"
+
+enum vector {
+	EXCPTN_RST,
+	EXCPTN_UND,
+	EXCPTN_SVC,
+	EXCPTN_PABT,
+	EXCPTN_DABT,
+	EXCPTN_ADDREXCPTN,
+	EXCPTN_IRQ,
+	EXCPTN_FIQ,
+	EXCPTN_MAX,
+};
+
+typedef void (*exception_fn)(struct pt_regs *);
+extern void install_exception_handler(enum vector v, exception_fn fn);
+
+extern void show_regs(struct pt_regs *regs);
+extern void *get_sp(void);
+
+static inline unsigned long current_cpsr(void)
+{
+	unsigned long cpsr;
+	asm volatile("mrs %0, cpsr" : "=r" (cpsr));
+	return cpsr;
+}
+
+#define current_mode() (current_cpsr() & MODE_MASK)
+
+extern void
+phys_start_usr(size_t stacksize, void (*func)(void *arg), void *arg);
+
+#endif /* _ASMARM_PROCESSOR_H_ */
diff --git a/lib/arm/processor.c b/lib/arm/processor.c
new file mode 100644
index 0000000000000..3d38ea6f9fd73
--- /dev/null
+++ b/lib/arm/processor.c
@@ -0,0 +1,115 @@
+/*
+ * processor control and status functions
+ *
+ * Copyright (C) 2014, Red Hat Inc, Andrew Jones <drjones@xxxxxxxxxx>
+ *
+ * This work is licensed under the terms of the GNU LGPL, version 2.
+ */
+#include "libcflat.h"
+#include "asm/setup.h"
+#include "asm/ptrace.h"
+#include "asm/processor.h"
+
+static const char *processor_modes[] = {
+	"USER_26", "FIQ_26" , "IRQ_26" , "SVC_26" ,
+	"UK4_26" , "UK5_26" , "UK6_26" , "UK7_26" ,
+	"UK8_26" , "UK9_26" , "UK10_26", "UK11_26",
+	"UK12_26", "UK13_26", "UK14_26", "UK15_26",
+	"USER_32", "FIQ_32" , "IRQ_32" , "SVC_32" ,
+	"UK4_32" , "UK5_32" , "UK6_32" , "ABT_32" ,
+	"UK8_32" , "UK9_32" , "UK10_32", "UND_32" ,
+	"UK12_32", "UK13_32", "UK14_32", "SYS_32"
+};
+
+static char *vector_names[] = {
+	"rst", "und", "svc", "pabt", "dabt", "addrexcptn", "irq", "fiq"
+};
+
+void show_regs(struct pt_regs *regs)
+{
+	unsigned long flags;
+	char buf[64];
+
+	printf("pc : [<%08lx>]    lr : [<%08lx>]    psr: %08lx\n"
+	       "sp : %08lx  ip : %08lx  fp : %08lx\n",
+		regs->ARM_pc, regs->ARM_lr, regs->ARM_cpsr,
+		regs->ARM_sp, regs->ARM_ip, regs->ARM_fp);
+	printf("r10: %08lx  r9 : %08lx  r8 : %08lx\n",
+		regs->ARM_r10, regs->ARM_r9, regs->ARM_r8);
+	printf("r7 : %08lx  r6 : %08lx  r5 : %08lx  r4 : %08lx\n",
+		regs->ARM_r7, regs->ARM_r6, regs->ARM_r5, regs->ARM_r4);
+	printf("r3 : %08lx  r2 : %08lx  r1 : %08lx  r0 : %08lx\n",
+		regs->ARM_r3, regs->ARM_r2, regs->ARM_r1, regs->ARM_r0);
+
+	flags = regs->ARM_cpsr;
+	buf[0] = flags & PSR_N_BIT ? 'N' : 'n';
+	buf[1] = flags & PSR_Z_BIT ? 'Z' : 'z';
+	buf[2] = flags & PSR_C_BIT ? 'C' : 'c';
+	buf[3] = flags & PSR_V_BIT ? 'V' : 'v';
+	buf[4] = '\0';
+
+	printf("Flags: %s  IRQs o%s  FIQs o%s  Mode %s\n",
+		buf, interrupts_enabled(regs) ? "n" : "ff",
+		fast_interrupts_enabled(regs) ? "n" : "ff",
+		processor_modes[processor_mode(regs)]);
+
+	if (!user_mode(regs)) {
+		unsigned int ctrl, transbase, dac;
+		asm volatile(
+			"mrc p15, 0, %0, c1, c0\n"
+			"mrc p15, 0, %1, c2, c0\n"
+			"mrc p15, 0, %2, c3, c0\n"
+		: "=r" (ctrl), "=r" (transbase), "=r" (dac));
+		printf("Control: %08x  Table: %08x  DAC: %08x\n",
+			ctrl, transbase, dac);
+	}
+}
+
+void *get_sp(void)
+{
+	register unsigned long sp asm("sp");
+	return (void *)sp;
+}
+
+static exception_fn exception_handlers[EXCPTN_MAX];
+
+void install_exception_handler(enum vector v, exception_fn fn)
+{
+	if (v < EXCPTN_MAX)
+		exception_handlers[v] = fn;
+}
+
+void do_handle_exception(enum vector v, struct pt_regs *regs)
+{
+	if (v < EXCPTN_MAX && exception_handlers[v]) {
+		exception_handlers[v](regs);
+		return;
+	}
+
+	if (v < EXCPTN_MAX)
+		printf("Unhandled exception %d (%s)\n", v, vector_names[v]);
+	else
+		printf("%s called with vector=%d\n", __func__, v);
+
+	printf("Exception frame registers:\n");
+	show_regs(regs);
+	abort();
+}
+
+void phys_start_usr(size_t stacksize, void (*func)(void *arg), void *arg)
+{
+	struct memregion *m = memregion_new(stacksize);
+	unsigned long sp_usr = (unsigned long)(m->addr + m->size);
+
+	sp_usr &= (~7UL); /* stack ptr needs 8-byte alignment */
+
+	asm volatile(
+		"mrs	r0, cpsr\n"
+		"bic	r0, #" __stringify(MODE_MASK) "\n"
+		"orr	r0, #" __stringify(USR_MODE) "\n"
+		"msr	cpsr_c, r0\n"
+		"mov	r0, %0\n"
+		"mov	sp, %1\n"
+		"mov	pc, %2\n"
+	:: "r" (arg), "r" (sp_usr), "r" (func) : "r0");
+}
diff --git a/lib/libcflat.h b/lib/libcflat.h
index f6c071c71f0b9..fec6762dd53fb 100644
--- a/lib/libcflat.h
+++ b/lib/libcflat.h
@@ -66,4 +66,7 @@ do {									\
 		abort();						\
 } while (0)
 
+#define __stringify_1(x...)	#x
+#define __stringify(x...)	__stringify_1(x)
+
 #endif
-- 
1.8.1.4

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