cortex-m: Generate vector table in C

Different versions of the linker behave differently when mixing object
built with lto enabled (desirable for code size reduction) and disabled
(assembler code), especially when they refer to each other symbols:

The file evaluation order of the linker becomes important as it
eliminates dead code at various points in time, and LTO code referring
to non-LTO code or vice versa, is not visible at early runs.

Sadly, just changing the order on the command line isn't sufficient:
What works for gcc8 breaks gcc6 (and may behave different in even more
ways on gcc4 or other versions).

Therefore, implement the vector table in C, so it's compiled in LTO
mode, just like the code it refers to.

BUG=b:65441143
BRANCH=none
TEST=with this change coral EC is functional when built with the gcc 8.1
based coreboot toolchain.

Change-Id: I9b75f6558f0357e18000ff1161096c8f9c94a8ac
Signed-off-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-on: https://chromium-review.googlesource.com/1120333
Commit-Ready: Patrick Georgi <pgeorgi@chromium.org>
Tested-by: Patrick Georgi <pgeorgi@chromium.org>
Reviewed-by: Stefan Reinauer <reinauer@chromium.org>

1 files changed, 382 insertions, 0 deletions

diff --git a/core/cortex-m/vecttable.c b/core/cortex-m/vecttable.c
new file mode 100644
index 0000000000..7db4a0eeca
--- /dev/null
+++ b/core/cortex-m/vecttable.c
@@ -0,0 +1,382 @@
+/* Copyright (c) 2018 The Chromium OS Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ *
+ * Cortex-M CPU vector table
+ */
+
+#ifndef ___INIT
+#define ___INIT
+#include "config.h"
+#include <task.h>
+#endif
+
+typedef void (*func)(void);
+
+#ifndef PASS
+#define PASS 1
+#endif
+
+#if PASS == 1
+/* Default exception handler */
+void __attribute__((used,naked)) default_handler(void);
+void default_handler()
+{
+	asm(
+	".thumb_func\n"
+	"	b exception_panic"
+	);
+}
+
+#define table(x) x
+
+#define weak_with_default __attribute__((used,weak,alias("default_handler")))
+
+#define vec(name) extern void weak_with_default name ## _handler(void);
+#define irq(num) vec(irq_ ## num)
+
+#define item(name) extern void name(void);
+#define null
+
+extern void stack_end(void); /* not technically correct, it's just a pointer */
+extern void reset(void);
+
+#pragma GCC diagnostic push
+#if __GNUC__ >= 6
+#pragma GCC diagnostic ignored "-Wattribute-alias"
+#endif
+/* Call default_handler if svc_handler is not found (task.c is not built) */
+void weak_with_default svc_handler(int desched, task_id_t resched);
+#pragma GCC diagnostic pop
+
+/*
+ * SVC handler helper
+ *
+ * Work around issue where a late exception can corrupt r0 to r3,
+ * see section 2.7 (svc) of Cortex-M3 Application Note 179:
+ * http://infocenter.arm.com/help/topic/com.arm.doc.dai0179b/AppsNote179.pdf
+ *
+ * This approach differs slightly from the one in the document,
+ * it only loads r0 (desched) and r1 (resched) for svc_handler.
+ */
+void __attribute__((used,naked)) svc_helper_handler(void);
+void svc_helper_handler()
+{
+	asm(
+	".thumb_func\n"
+	"	tst lr, #4		/* see if called from supervisor mode */\n"
+	"	mrs r2, msp		/* get the correct stack pointer into r2 */\n"
+	"	it ne\n"
+	"	mrsne r2, psp\n"
+	"	ldr r1, [r2, #4]	/* get regs from stack frame */\n"
+	"	ldr r0, [r2]\n"
+	"	b %0			/* call svc_handler */\n"
+	:
+	: "i"(svc_handler)
+	);
+}
+
+#endif /* PASS 1 */
+
+#if PASS == 2
+#undef table
+#undef vec
+#undef irq
+#undef item
+#undef null
+
+/* number of elements before the first irq vector */
+#define IRQ_OFFSET 16
+/* element in the table that is null: extra IRQs are routed there,
+ * then finally overwritten
+ */
+#define IRQ_UNUSED_OFFSET 8
+
+#define table(x) func vectors[] __attribute__((section(".text.vecttable,\"a\" @"))) = { x [IRQ_UNUSED_OFFSET] = null };
+
+#define vec(name) name ## _handler,
+#define irq(num) [num < CONFIG_IRQ_COUNT ? num + IRQ_OFFSET : IRQ_UNUSED_OFFSET] = vec(irq_ ## num)
+
+#define item(name) name,
+#define null (void*)0,
+#endif /* PASS 2 */
+
+table(
+	item(stack_end)
+	item(reset)
+	vec(nmi)
+	vec(hard_fault)
+	vec(mpu_fault)
+	vec(bus_fault)
+	vec(usage_fault)
+	null
+	null
+	null
+	null
+	item(svc_helper_handler)
+	vec(debug)
+	null
+	vec(pendsv)
+	vec(sys_tick)
+	irq(0)
+	irq(1)
+	irq(2)
+	irq(3)
+	irq(4)
+	irq(5)
+	irq(6)
+	irq(7)
+	irq(8)
+	irq(9)
+	irq(10)
+	irq(11)
+	irq(12)
+	irq(13)
+	irq(14)
+	irq(15)
+	irq(16)
+	irq(17)
+	irq(18)
+	irq(19)
+	irq(20)
+	irq(21)
+	irq(22)
+	irq(23)
+	irq(24)
+	irq(25)
+	irq(26)
+	irq(27)
+	irq(28)
+	irq(29)
+	irq(30)
+	irq(31)
+	irq(32)
+	irq(33)
+	irq(34)
+	irq(35)
+	irq(36)
+	irq(37)
+	irq(38)
+	irq(39)
+	irq(40)
+	irq(41)
+	irq(42)
+	irq(43)
+	irq(44)
+	irq(45)
+	irq(46)
+	irq(47)
+	irq(48)
+	irq(49)
+	irq(50)
+	irq(51)
+	irq(52)
+	irq(53)
+	irq(54)
+	irq(55)
+	irq(56)
+	irq(57)
+	irq(58)
+	irq(59)
+	irq(60)
+	irq(61)
+	irq(62)
+	irq(63)
+	irq(64)
+	irq(65)
+	irq(66)
+	irq(67)
+	irq(68)
+	irq(69)
+	irq(70)
+	irq(71)
+	irq(72)
+	irq(73)
+	irq(74)
+	irq(75)
+	irq(76)
+	irq(77)
+	irq(78)
+	irq(79)
+	irq(80)
+	irq(81)
+	irq(82)
+	irq(83)
+	irq(84)
+	irq(85)
+	irq(86)
+	irq(87)
+	irq(88)
+	irq(89)
+	irq(90)
+	irq(91)
+	irq(92)
+	irq(93)
+	irq(94)
+	irq(95)
+	irq(96)
+	irq(97)
+	irq(98)
+	irq(99)
+	irq(100)
+	irq(101)
+	irq(102)
+	irq(103)
+	irq(104)
+	irq(105)
+	irq(106)
+	irq(107)
+	irq(108)
+	irq(109)
+	irq(110)
+	irq(111)
+	irq(112)
+	irq(113)
+	irq(114)
+	irq(115)
+	irq(116)
+	irq(117)
+	irq(118)
+	irq(119)
+	irq(120)
+	irq(121)
+	irq(122)
+	irq(123)
+	irq(124)
+	irq(125)
+	irq(126)
+	irq(127)
+	irq(128)
+	irq(129)
+	irq(130)
+	irq(131)
+	irq(132)
+	irq(133)
+	irq(134)
+	irq(135)
+	irq(136)
+	irq(137)
+	irq(138)
+	irq(139)
+	irq(140)
+	irq(141)
+	irq(142)
+	irq(143)
+	irq(144)
+	irq(145)
+	irq(146)
+	irq(147)
+	irq(148)
+	irq(149)
+	irq(150)
+	irq(151)
+	irq(152)
+	irq(153)
+	irq(154)
+	irq(155)
+	irq(156)
+	irq(157)
+	irq(158)
+	irq(159)
+	irq(160)
+	irq(161)
+	irq(162)
+	irq(163)
+	irq(164)
+	irq(165)
+	irq(166)
+	irq(167)
+	irq(168)
+	irq(169)
+	irq(170)
+	irq(171)
+	irq(172)
+	irq(173)
+	irq(174)
+	irq(175)
+	irq(176)
+	irq(177)
+	irq(178)
+	irq(179)
+	irq(180)
+	irq(181)
+	irq(182)
+	irq(183)
+	irq(184)
+	irq(185)
+	irq(186)
+	irq(187)
+	irq(188)
+	irq(189)
+	irq(190)
+	irq(191)
+	irq(192)
+	irq(193)
+	irq(194)
+	irq(195)
+	irq(196)
+	irq(197)
+	irq(198)
+	irq(199)
+	irq(200)
+	irq(201)
+	irq(202)
+	irq(203)
+	irq(204)
+	irq(205)
+	irq(206)
+	irq(207)
+	irq(208)
+	irq(209)
+	irq(210)
+	irq(211)
+	irq(212)
+	irq(213)
+	irq(214)
+	irq(215)
+	irq(216)
+	irq(217)
+	irq(218)
+	irq(219)
+	irq(220)
+	irq(221)
+	irq(222)
+	irq(223)
+	irq(224)
+	irq(225)
+	irq(226)
+	irq(227)
+	irq(228)
+	irq(229)
+	irq(230)
+	irq(231)
+	irq(232)
+	irq(233)
+	irq(234)
+	irq(235)
+	irq(236)
+	irq(237)
+	irq(238)
+	irq(239)
+	irq(240)
+	irq(241)
+	irq(242)
+	irq(243)
+	irq(244)
+	irq(245)
+	irq(246)
+	irq(247)
+	irq(248)
+	irq(249)
+	irq(250)
+	irq(251)
+	irq(252)
+	irq(253)
+	irq(254)
+)
+
+#if PASS == 1
+#undef PASS
+#define PASS 2
+#include "vecttable.c"
+#endif