Msg/ClobberedRA - Revision history

Henry at 03:50, 17 March 2019

2019-03-17T03:50:06Z

← Older revision		Revision as of 03:50, 17 March 2019
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	==== ARMv7 ====		==== ARMv7 ====

	<syntaxhighlight lang="Asm" line highlight="11">		<syntaxhighlight lang="Asm" line highlight="10">
	.global _start		.global _start
	_start:		_start:
	~~mov sp, #0x1000 // Initialize SP to something sane~~
	bl MyFunction		bl MyFunction
	nop // Should return here		nop // Should return here
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	</syntaxhighlight>		</syntaxhighlight>
	==== Nios II ====		==== Nios II ====
	<syntaxhighlight lang="Asm" line highlight="10">		<syntaxhighlight lang="Asm" line highlight="9">
	.global _start		.global _start
	_start:		_start:
	~~movi sp, 0x1000 # Initialize SP~~
	call Function		call Function
	nop # Should return here		nop # Should return here
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	ret # return to a different location		ret # return to a different location
	</syntaxhighlight>		</syntaxhighlight>

			==== MIPS ====
			<syntaxhighlight lang="Asm" line highlight="9">
			.global _start
			_start:
			jal Function
			nop # Should return here
			nop # Actually returns here

			Function:
			addiu $ra, $ra, 4 # Modify ra
			jr $ra # return to a different location
			</syntaxhighlight>


	=== Debugging ===		=== Debugging ===

Henry at 09:58, 10 March 2019

2019-03-10T09:58:01Z

← Older revision		Revision as of 09:58, 10 March 2019
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	=== Debugging ===		=== Debugging ===
	* ~~Fundamentally, this~~ message is complaining that the return address differs between the start of the function and at the function return. Use breakpoints and make a note of the value of the return address (ra or lr) at both the function entry and return. Are they the same?		* This message is complaining that the return address (or link address for ARM) differs between the start of the function and at the function return. Use breakpoints and make a note of the value of the return address (ra or lr) at both the function entry and return. Are they the same?
	* Typically, the return address register is not used in a function body except for saving and restoring it to the stack ~~due to the need for~~ a nested function call. A common cause of the return address changing is a problem during save and restore, e.g., popping from a different location than the corresponding push, or modifying the value that was on the stack. Watch the return address's save and restore and ensure that both the location on the stack and values are the same.		* Typically, the return address register is not used in a function body except for saving and restoring it to the stack when there is a nested function call. A common cause of the return address changing is a problem during save and restore, e.g., popping from a different location than the corresponding push, or modifying the value that was on the stack. Watch the return address's save and restore and ensure that both the location on the stack and values are the same.

	=== Implementation ===		=== Implementation ===

Henry at 09:54, 10 March 2019

2019-03-10T09:54:54Z

← Older revision		Revision as of 09:54, 10 March 2019
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	A function should normally return to the instruction after the call instruction in the caller that called this function. This message tells you that this didn't happen: the function return is returning somewhere other than the instruction following the matching call.		A function should normally return to the instruction after the call instruction in the caller that called this function. This message tells you that this didn't happen: the function return is returning somewhere other than the instruction following the matching call.

	If you clobbered sp, see also [[Msg/ClobberedSP]]		If you also clobbered sp, see also [[Msg/ClobberedSP]]

	=== Examples ===		=== Examples ===

Henry at 07:40, 10 March 2019

2019-03-10T07:40:18Z

← Older revision		Revision as of 07:40, 10 March 2019
Line 1:		Line 1:
	A function should normally return to the instruction after the call instruction in the caller that called this function. This message tells you that this didn't happen: the function return is returning somewhere other than the instruction following the matching call.		A function should normally return to the instruction after the call instruction in the caller that called this function. This message tells you that this didn't happen: the function return is returning somewhere other than the instruction following the matching call.

			If you clobbered sp, see also [[Msg/ClobberedSP]]

	=== Examples ===		=== Examples ===

Henry at 07:13, 10 March 2019

2019-03-10T07:13:59Z

← Older revision		Revision as of 07:13, 10 March 2019
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	{{DisableMsg\|Function clobbered ra or sp}}		{{DisableMsg\|Function clobbered ra or sp}}

			ARMv7: <b>Function clobbered sp, or bad return</b>

Henry: /* Examples */

2019-03-10T07:13:00Z

Examples

← Older revision		Revision as of 07:13, 10 March 2019
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	Function:		Function:
	addi ra, ra, 4 # Modify ra		addi ra, ra, 4 # Modify ra
	ret # return to a different location		ret # return to a different location
	</syntaxhighlight>		</syntaxhighlight>

Henry: /* Examples */

2019-03-10T07:12:52Z

Examples

← Older revision		Revision as of 07:12, 10 March 2019
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	MyFunction:		MyFunction:
	add lr, #4 // Change LR		add lr, #4 // Change LR
	bx lr // return to a different location		bx lr // return to a different location
	</syntaxhighlight>		</syntaxhighlight>
	==== Nios II ====		==== Nios II ====

Henry: /* Examples */

2019-03-10T07:12:43Z

Examples

← Older revision		Revision as of 07:12, 10 March 2019
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	mov sp, #0x1000 // Initialize SP to something sane		mov sp, #0x1000 // Initialize SP to something sane
	bl MyFunction		bl MyFunction
	nop // Should return here		nop // Should return here
	nop // Actually returns here		nop // Actually returns here
	# ...		# ...

	MyFunction:		MyFunction:
	add lr, #4 // Change LR		add lr, #4 // Change LR
	bx lr // return to a different location		bx lr // return to a different location
	</syntaxhighlight>		</syntaxhighlight>
	==== Nios II ====		==== Nios II ====

Henry: Henry moved page Msgs/ClobberedRA to Msg/ClobberedRA without leaving a redirect

2019-03-10T01:09:56Z

Henry moved page Msgs/ClobberedRA to Msg/ClobberedRA without leaving a redirect

← Older revision	Revision as of 01:09, 10 March 2019
(No difference)

Henry: /* Examples */

2019-03-10T01:04:03Z

Examples

← Older revision		Revision as of 01:04, 10 March 2019
Line 9:		Line 9:
	mov sp, #0x1000 // Initialize SP to something sane		mov sp, #0x1000 // Initialize SP to something sane
	bl MyFunction		bl MyFunction
	nop // Should return here		nop // Should return here
	nop // Actually returns here		nop // Actually returns here
	# ...		# ...

	MyFunction:		MyFunction:
	add lr, #4 // Change LR		add lr, #4 // Change LR
	bx lr // return to a different location		bx lr // return to a different location
	</syntaxhighlight>		</syntaxhighlight>
	==== Nios II ====		==== Nios II ====
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	movi sp, 0x1000 # Initialize SP		movi sp, 0x1000 # Initialize SP
	call Function		call Function
	nop # Should return here		nop # Should return here
	nop # Actually returns here		nop # Actually returns here

	Function:		Function: