Msg/FetchBadPC - Revision history

Henry: /* ARMv7 */

2019-03-17T04:00:04Z

ARMv7

← Older revision		Revision as of 04:00, 17 March 2019
Line 11:		Line 11:
	nop		nop
	</syntaxhighlight>		</syntaxhighlight>
	(~~The~~ example uses two nops in the .text section for ARM because the assembler pads the length of the .text section to a multiple of 8 bytes.)		(This example uses two nops in the .text section for ARM because the assembler pads the length of the .text section to a multiple of 8 bytes.)

	==== Nios II ====		==== Nios II ====

Henry: /* ARMv7 */

2019-03-17T03:59:55Z

ARMv7

← Older revision		Revision as of 03:59, 17 March 2019
Line 11:		Line 11:
	nop		nop
	</syntaxhighlight>		</syntaxhighlight>
			(The example uses two nops in the .text section for ARM because the assembler pads the length of the .text section to a multiple of 8 bytes.)

	==== Nios II ====		==== Nios II ====
	<syntaxhighlight line lang="Asm" highlight="5">		<syntaxhighlight line lang="Asm" highlight="5">

Henry at 03:57, 17 March 2019

2019-03-17T03:57:30Z

← Older revision		Revision as of 03:57, 17 March 2019
Line 20:		Line 20:
	</syntaxhighlight>		</syntaxhighlight>

	As the examples above show, one of the common reasons for encountering this warning is that the program runs past the end of the <code>.text</code> section and starts executing in the <code>.data</code> section. Although the first 32-bit word of the <code>.data</code> section is a valid opcode, executing instructions from the <code>.data</code> section is usually unintended.		==== MIPS ====
			<syntaxhighlight line lang="Asm" highlight="5">
			.global _start
			_start:
			nop
			.data
			nop
			</syntaxhighlight>

			As the examples above show, one of the common reasons for encountering this warning is that the program runs past the end of the <code>.text</code> section and starts executing in the <code>.data</code> section. Although the first 32-bit word of the <code>.data</code> section is a valid opcode in this example, executing instructions from the <code>.data</code> section is usually unintended.

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

Henry: Created page with "Normally, the CPU should execute code that came from a code section (such as `.text`) from an executable file generated by an assembler or compiler. This message te..."

2019-03-11T06:26:00Z

Created page with "Normally, the CPU should execute code that came from a code section (such as <code>.text</code>) from an executable file generated by an assembler or compiler. This message te..."

New page

Normally, the CPU should execute code that came from a code section (such as <code>.text</code>) from an executable file generated by an assembler or compiler. This message tells you that the simulator thinks you're currently executing outside a code section.

=== Examples ===
==== ARMv7 ====
<syntaxhighlight line lang="Asm" highlight="6">
.global _start
_start:
nop
nop
.data
nop
</syntaxhighlight>
==== Nios II ====
<syntaxhighlight line lang="Asm" highlight="5">
.global _start
_start:
nop
.data
nop
</syntaxhighlight>

As the examples above show, one of the common reasons for encountering this warning is that the program runs past the end of the <code>.text</code> section and starts executing in the <code>.data</code> section. Although the first 32-bit word of the <code>.data</code> section is a valid opcode, executing instructions from the <code>.data</code> section is usually unintended.

=== Debugging ===
* As in the examples above, make sure your program isn't executing past the end of the <code>.text</code> section.
* Executing from a bad location could also be due to a branch with an incorrect target address. To find the offending branch, try using the [https://cpulator.01xz.net/doc/#callstack <b>Trace window</b>] (located in the same panel as the registers window by default) to look backwards in the program execution.

=== Implementation ===
ELF executables contain "sections" of bytes that define where in memory each blob of bytes in the executable should be loaded. The ELF executable also includes information on whether each section is intended for executable code (e.g., the <code>.text</code> section contains code) or for data (the <code>.data</code> section is marked as containing data). The simulator tracks the sections defined in the most recently loaded ELF executable, and checks each instruction fetch against the sections. This message is generated at the instruction fetch.

There may be uncommon cases where the simulator's idea of what is a code section doesn't match reality, and you may want to disable this warning. Some examples:
* Your program writes code into a data section and then executes it. In this case, executing from a data section really is the right thing to do.
* Your program has multiple ELF executables. The simulator uses the section boundaries defined in the most recently loaded ELF executable.

{{DisableMsg|Instruction fetch: Outside a code section}}

Msg/FetchBadPC - Revision history

Henry: /* ARMv7 */

Henry: /* ARMv7 */

Henry at 03:57, 17 March 2019

Henry: Created page with "Normally, the CPU should execute code that came from a code section (such as .text) from an executable file generated by an assembler or compiler. This message te..."

Henry: Created page with "Normally, the CPU should execute code that came from a code section (such as `.text`) from an executable file generated by an assembler or compiler. This message te..."