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2023-12-09 95099d4622f8cb224d94e314c7a8e0df60b13f87

 kernel/arch/arm/kernel/entry-ftrace.S
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@@ -1,8 +1,4 @@
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-/*
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- * This program is free software; you can redistribute it and/or modify
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- * it under the terms of the GNU General Public License version 2 as
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- * published by the Free Software Foundation.
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- */
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+/* SPDX-License-Identifier: GPL-2.0-only */
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 #include <asm/assembler.h>
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 #include <asm/ftrace.h>
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@@ -15,23 +11,8 @@
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  * start of every function.  In mcount, apart from the function's address (in
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  * lr), we need to get hold of the function's caller's address.
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  *
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- * Older GCCs (pre-4.4) inserted a call to a routine called mcount like this:
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- *
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- *	bl	mcount
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- *
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- * These versions have the limitation that in order for the mcount routine to
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- * be able to determine the function's caller's address, an APCS-style frame
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- * pointer (which is set up with something like the code below) is required.
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- *
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- *	mov     ip, sp
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- *	push    {fp, ip, lr, pc}
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- *	sub     fp, ip, #4
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- *
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- * With EABI, these frame pointers are not available unless -mapcs-frame is
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- * specified, and if building as Thumb-2, not even then.
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- *
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- * Newer GCCs (4.4+) solve this problem by introducing a new version of mcount,
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- * with call sites like:
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+ * Newer GCCs (4.4+) solve this problem by using a version of mcount with call
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+ * sites like:
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  *
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  *	push	{lr}
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  *	bl	__gnu_mcount_nc
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@@ -41,21 +22,11 @@
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  * mcount can be thought of as a function called in the middle of a subroutine
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  * call.  As such, it needs to be transparent for both the caller and the
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  * callee: the original lr needs to be restored when leaving mcount, and no
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- * registers should be clobbered.  (In the __gnu_mcount_nc implementation, we
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- * clobber the ip register.  This is OK because the ARM calling convention
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- * allows it to be clobbered in subroutines and doesn't use it to hold
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- * parameters.)
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+ * registers should be clobbered.
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  *
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- * When using dynamic ftrace, we patch out the mcount call by a "mov r0, r0"
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- * for the mcount case, and a "pop {lr}" for the __gnu_mcount_nc case (see
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- * arch/arm/kernel/ftrace.c).
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+ * When using dynamic ftrace, we patch out the mcount call by a "pop {lr}"
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+ * instead of the __gnu_mcount_nc call (see arch/arm/kernel/ftrace.c).
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  */
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-
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-#ifndef CONFIG_OLD_MCOUNT
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-#if (__GNUC__ < 4 || (__GNUC__ == 4 && __GNUC_MINOR__ < 4))
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-#error Ftrace requires CONFIG_FRAME_POINTER=y with GCC older than 4.4.0.
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-#endif
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-#endif
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 .macro mcount_adjust_addr rd, rn
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 	bic	\rd, \rn, #1		@ clear the Thumb bit if present
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@@ -96,26 +67,25 @@
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 .macro __ftrace_regs_caller
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-	sub	sp, sp, #8	@ space for PC and CPSR OLD_R0,
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+	str	lr, [sp, #-8]!	@ store LR as PC and make space for CPSR/OLD_R0,
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 				@ OLD_R0 will overwrite previous LR
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-	add 	ip, sp, #12	@ move in IP the value of SP as it was
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-				@ before the push {lr} of the mcount mechanism
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-
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-	str     lr, [sp, #0]    @ store LR instead of PC
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-
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-	ldr     lr, [sp, #8]    @ get previous LR
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+	ldr	lr, [sp, #8]    @ get previous LR
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 	str	r0, [sp, #8]	@ write r0 as OLD_R0 over previous LR
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-	stmdb   sp!, {ip, lr}
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-	stmdb   sp!, {r0-r11, lr}
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+	str	lr, [sp, #-4]!	@ store previous LR as LR
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+
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+	add 	lr, sp, #16	@ move in LR the value of SP as it was
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+				@ before the push {lr} of the mcount mechanism
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+
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+	push	{r0-r11, ip, lr}
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 	@ stack content at this point:
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 	@ 0  4          48   52       56            60   64    68       72
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-	@ R0 | R1 | ... | LR | SP + 4 | previous LR | LR | PSR | OLD_R0 |
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+	@ R0 | R1 | ... | IP | SP + 4 | previous LR | LR | PSR | OLD_R0 |
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-	mov r3, sp				@ struct pt_regs*
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+	mov	r3, sp				@ struct pt_regs*
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 	ldr r2, =function_trace_op
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 	ldr r2, [r2]				@ pointer to the current
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@@ -138,11 +108,9 @@
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 #endif
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 	@ pop saved regs
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-	ldmia   sp!, {r0-r12}			@ restore r0 through r12
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-	ldr	ip, [sp, #8]			@ restore PC
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-	ldr	lr, [sp, #4]			@ restore LR
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-	ldr	sp, [sp, #0]			@ restore SP
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-	mov	pc, ip				@ return
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+	pop	{r0-r11, ip, lr}		@ restore r0 through r12
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+	ldr	lr, [sp], #4			@ restore LR
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+	ldr	pc, [sp], #12
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 .endm
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 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
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 	bl	prepare_ftrace_return
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 	@ pop registers saved in ftrace_regs_caller
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-	ldmia   sp!, {r0-r12}			@ restore r0 through r12
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-	ldr	ip, [sp, #8]			@ restore PC
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-	ldr	lr, [sp, #4]			@ restore LR
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-	ldr	sp, [sp, #0]			@ restore SP
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-	mov	pc, ip				@ return
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+	pop	{r0-r11, ip, lr}		@ restore r0 through r12
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+	ldr	lr, [sp], #4			@ restore LR
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+	ldr	pc, [sp], #12
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 .endm
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 #endif
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 	mcount_exit
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 .endm
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-#ifdef CONFIG_OLD_MCOUNT
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-/*
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- * mcount
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- */
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-
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-.macro mcount_enter
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-	stmdb	sp!, {r0-r3, lr}
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-.endm
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-
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-.macro mcount_get_lr reg
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-	ldr	\reg, [fp, #-4]
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-.endm
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-
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-.macro mcount_exit
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-	ldr	lr, [fp, #-4]
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-	ldmia	sp!, {r0-r3, pc}
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-.endm
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-
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-ENTRY(mcount)
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-#ifdef CONFIG_DYNAMIC_FTRACE
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-	stmdb	sp!, {lr}
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-	ldr	lr, [fp, #-4]
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-	ldmia	sp!, {pc}
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-#else
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-	__mcount _old
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-#endif
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-ENDPROC(mcount)
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-
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-#ifdef CONFIG_DYNAMIC_FTRACE
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-ENTRY(ftrace_caller_old)
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-	__ftrace_caller _old
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-ENDPROC(ftrace_caller_old)
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-#endif
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-
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-#ifdef CONFIG_FUNCTION_GRAPH_TRACER
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-ENTRY(ftrace_graph_caller_old)
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-	__ftrace_graph_caller
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-ENDPROC(ftrace_graph_caller_old)
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-#endif
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-
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-.purgem mcount_enter
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-.purgem mcount_get_lr
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-.purgem mcount_exit
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-#endif
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-
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 /*
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  * __gnu_mcount_nc
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  */
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 .endm
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 .macro mcount_exit
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-	ldmia	sp!, {r0-r3, ip, lr}
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-	ret	ip
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+	ldmia	sp!, {r0-r3}
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+	ldr	lr, [sp, #4]
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+	ldr	pc, [sp], #8
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 .endm
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 ENTRY(__gnu_mcount_nc)
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 UNWIND(.fnstart)
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 #ifdef CONFIG_DYNAMIC_FTRACE
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-	mov	ip, lr
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-	ldmia	sp!, {lr}
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-	ret	ip
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+	push	{lr}
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+	ldr	lr, [sp, #4]
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+	ldr	pc, [sp], #8
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 #else
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 	__mcount
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 #endif