Adding upstream version 5.10.209.upstream/5.10.209upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 222 insertions, 0 deletions

diff --git a/arch/arm/lib/backtrace-clang.S b/arch/arm/lib/backtrace-clang.S
new file mode 100644
index 000000000..6174c45f5
--- /dev/null
+++ b/arch/arm/lib/backtrace-clang.S
@@ -0,0 +1,222 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ *  linux/arch/arm/lib/backtrace-clang.S
+ *
+ *  Copyright (C) 2019 Nathan Huckleberry
+ *
+ */
+#include <linux/kern_levels.h>
+#include <linux/linkage.h>
+#include <asm/assembler.h>
+		.text
+
+/* fp is 0 or stack frame */
+
+#define frame	r4
+#define sv_fp	r5
+#define sv_pc	r6
+#define mask	r7
+#define sv_lr	r8
+#define loglvl	r9
+
+ENTRY(c_backtrace)
+
+#if !defined(CONFIG_FRAME_POINTER) || !defined(CONFIG_PRINTK)
+		ret	lr
+ENDPROC(c_backtrace)
+#else
+
+
+/*
+ * Clang does not store pc or sp in function prologues so we don't know exactly
+ * where the function starts.
+ *
+ * We can treat the current frame's lr as the saved pc and the preceding
+ * frame's lr as the current frame's lr, but we can't trace the most recent
+ * call.  Inserting a false stack frame allows us to reference the function
+ * called last in the stacktrace.
+ *
+ * If the call instruction was a bl we can look at the callers branch
+ * instruction to calculate the saved pc.  We can recover the pc in most cases,
+ * but in cases such as calling function pointers we cannot. In this case,
+ * default to using the lr. This will be some address in the function, but will
+ * not be the function start.
+ *
+ * Unfortunately due to the stack frame layout we can't dump r0 - r3, but these
+ * are less frequently saved.
+ *
+ * Stack frame layout:
+ * 		<larger addresses>
+ * 		saved lr
+ * 	frame=> saved fp
+ * 		optionally saved caller registers (r4 - r10)
+ * 		optionally saved arguments (r0 - r3)
+ * 		<top of stack frame>
+ * 		<smaller addresses>
+ *
+ * Functions start with the following code sequence:
+ * corrected pc =>  stmfd sp!, {..., fp, lr}
+ *		add fp, sp, #x
+ *		stmfd sp!, {r0 - r3} (optional)
+ *
+ *
+ *
+ *
+ *
+ *
+ * The diagram below shows an example stack setup for dump_stack.
+ *
+ * The frame for c_backtrace has pointers to the code of dump_stack. This is
+ * why the frame of c_backtrace is used to for the pc calculation of
+ * dump_stack. This is why we must move back a frame to print dump_stack.
+ *
+ * The stored locals for dump_stack are in dump_stack's frame. This means that
+ * to fully print dump_stack's frame we need both the frame for dump_stack (for
+ * locals) and the frame that was called by dump_stack (for pc).
+ *
+ * To print locals we must know where the function start is. If we read the
+ * function prologue opcodes we can determine which variables are stored in the
+ * stack frame.
+ *
+ * To find the function start of dump_stack we can look at the stored LR of
+ * show_stack. It points at the instruction directly after the bl dump_stack.
+ * We can then read the offset from the bl opcode to determine where the branch
+ * takes us.  The address calculated must be the start of dump_stack.
+ *
+ * c_backtrace frame           dump_stack:
+ * {[LR]    }  ============|   ...
+ * {[FP]    }  =======|    |   bl c_backtrace
+ *                    |    |=> ...
+ * {[R4-R10]}         |
+ * {[R0-R3] }         |        show_stack:
+ * dump_stack frame   |        ...
+ * {[LR]    } =============|   bl dump_stack
+ * {[FP]    } <=======|    |=> ...
+ * {[R4-R10]}
+ * {[R0-R3] }
+ */
+
+		stmfd	sp!, {r4 - r9, fp, lr}	@ Save an extra register
+						@ to ensure 8 byte alignment
+		movs	frame, r0		@ if frame pointer is zero
+		beq	no_frame		@ we have no stack frames
+		mov	loglvl, r2
+		tst	r1, #0x10		@ 26 or 32-bit mode?
+		moveq	mask, #0xfc000003
+		movne	mask, #0		@ mask for 32-bit
+
+/*
+ * Switches the current frame to be the frame for dump_stack.
+ */
+		add	frame, sp, #24		@ switch to false frame
+for_each_frame:	tst	frame, mask		@ Check for address exceptions
+		bne	no_frame
+
+/*
+ * sv_fp is the stack frame with the locals for the current considered
+ * function.
+ *
+ * sv_pc is the saved lr frame the frame above. This is a pointer to a code
+ * address within the current considered function, but it is not the function
+ * start. This value gets updated to be the function start later if it is
+ * possible.
+ */
+1001:		ldr	sv_pc, [frame, #4]	@ get saved 'pc'
+1002:		ldr	sv_fp, [frame, #0]	@ get saved fp
+
+		teq	sv_fp, mask		@ make sure next frame exists
+		beq	no_frame
+
+/*
+ * sv_lr is the lr from the function that called the current function. This is
+ * a pointer to a code address in the current function's caller.  sv_lr-4 is
+ * the instruction used to call the current function.
+ *
+ * This sv_lr can be used to calculate the function start if the function was
+ * called using a bl instruction. If the function start can be recovered sv_pc
+ * is overwritten with the function start.
+ *
+ * If the current function was called using a function pointer we cannot
+ * recover the function start and instead continue with sv_pc as an arbitrary
+ * value within the current function. If this is the case we cannot print
+ * registers for the current function, but the stacktrace is still printed
+ * properly.
+ */
+1003:		ldr	sv_lr, [sv_fp, #4]	@ get saved lr from next frame
+
+		ldr	r0, [sv_lr, #-4]	@ get call instruction
+		ldr	r3, .Lopcode+4
+		and	r2, r3, r0		@ is this a bl call
+		teq	r2, r3
+		bne	finished_setup		@ give up if it's not
+		and	r0, #0xffffff		@ get call offset 24-bit int
+		lsl	r0, r0, #8		@ sign extend offset
+		asr	r0, r0, #8
+		ldr	sv_pc, [sv_fp, #4]	@ get lr address
+		add	sv_pc, sv_pc, #-4	@ get call instruction address
+		add	sv_pc, sv_pc, #8	@ take care of prefetch
+		add	sv_pc, sv_pc, r0, lsl #2@ find function start
+
+finished_setup:
+
+		bic	sv_pc, sv_pc, mask	@ mask PC/LR for the mode
+
+/*
+ * Print the function (sv_pc) and where it was called from (sv_lr).
+ */
+1004:		mov	r0, sv_pc
+
+		mov	r1, sv_lr
+		mov	r2, frame
+		bic	r1, r1, mask		@ mask PC/LR for the mode
+		mov	r3, loglvl
+		bl	dump_backtrace_entry
+
+/*
+ * Test if the function start is a stmfd instruction to determine which
+ * registers were stored in the function prologue.
+ *
+ * If we could not recover the sv_pc because we were called through a function
+ * pointer the comparison will fail and no registers will print. Unwinding will
+ * continue as if there had been no registers stored in this frame.
+ */
+1005:		ldr	r1, [sv_pc, #0]		@ if stmfd sp!, {..., fp, lr}
+		ldr	r3, .Lopcode		@ instruction exists,
+		teq	r3, r1, lsr #11
+		ldr	r0, [frame]		@ locals are stored in
+						@ the preceding frame
+		subeq	r0, r0, #4
+		mov	r2, loglvl
+		bleq	dump_backtrace_stm	@ dump saved registers
+
+/*
+ * If we are out of frames or if the next frame is invalid.
+ */
+		teq	sv_fp, #0		@ zero saved fp means
+		beq	no_frame		@ no further frames
+
+		cmp	sv_fp, frame		@ next frame must be
+		mov	frame, sv_fp		@ above the current frame
+		bhi	for_each_frame
+
+1006:		adr	r0, .Lbad
+		mov	r1, loglvl
+		mov	r2, frame
+		bl	printk
+no_frame:	ldmfd	sp!, {r4 - r9, fp, pc}
+ENDPROC(c_backtrace)
+		.pushsection __ex_table,"a"
+		.align	3
+		.long	1001b, 1006b
+		.long	1002b, 1006b
+		.long	1003b, 1006b
+		.long	1004b, 1006b
+		.long   1005b, 1006b
+		.popsection
+
+.Lbad:		.asciz	"%sBacktrace aborted due to bad frame pointer <%p>\n"
+		.align
+.Lopcode:	.word	0xe92d4800 >> 11	@ stmfd sp!, {... fp, lr}
+		.word	0x0b000000		@ bl if these bits are set
+
+#endif