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https://github.com/cirosantilli/linux-kernel-module-cheat.git
synced 2026-01-26 11:41:35 +01:00
52 lines
1.2 KiB
ArmAsm
52 lines
1.2 KiB
ArmAsm
/* https://github.com/cirosantilli/arm-assembly-cheat#x31 */
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#include "common.h"
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ENTRY
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/* ERROR: can never use the name x31. */
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#if 0
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mov x31, 31
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#endif
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/* mov (register) is an alias for ORR, which accepts xzr. */
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mov x0, 1
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mov x0, xzr
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ASSERT_EQ(x0, 0)
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/* Same encoding as the mov version. */
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mov x0, 1
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orr x0, xzr, xzr
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ASSERT_EQ(x0, 0)
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/* So, orr, which is not an alias, can only take xzr, not sp. */
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#if 0
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orr sp, sp, sp
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#endif
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/* Zero register discards result if written to. */
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mov x0, 1
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orr xzr, x0, x0
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ASSERT_EQ(xzr, 0)
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/* MOV (to/from SP) is an alias for ADD (immediate). */
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mov x0, sp
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mov sp, 1
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/* Alias to add. */
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mov x1, sp
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/* Exact same encoding as above. */
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add x1, sp, 0
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ASSERT_EQ(x1, 1)
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mov sp, x0
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/* So, ADD (immediate), which is not an alias, can only take sp, not xzr. */
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#if 0
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/* Error: integer register expected in the extended/shifted operand register at operand 3 -- `add xzr,xzr,1' */
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add xzr, xzr, 1
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#endif
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/* Note however that ADD (register), unlike ADD (immediate),
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* does not say anything about SP, and so does accept xzr just fine.
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*/
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add xzr, xzr, xzr
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EXIT
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