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34 lines
962 B
ArmAsm
34 lines
962 B
ArmAsm
/* https://github.com/cirosantilli/linux-kernel-module-cheat#x86-data-transfer-instructions
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*
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* mov and zero extend
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*
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* unsigned typecast to larger types in 2's complement.
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*
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* MOV does this automatically from 32 to 64 bits:
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* https://stackoverflow.com/questions/11177137/why-do-x86-64-instructions-on-32-bit-registers-zero-the-upper-part-of-the-full-6
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*/
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#include <lkmc.h>
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LKMC_PROLOGUE
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/* Top bit is 0, extend with zero. */
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mov $0x1234567F, %eax
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movzx %al, %ax
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LKMC_ASSERT_EQ_32(%eax, $0x1234007F)
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/* Top bit is 1: does not matter, stil zero extends. */
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mov $0x1234568F, %eax
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movzx %al, %ax
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LKMC_ASSERT_EQ_32(%eax, $0x1234008F)
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#if 0
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/* must be a register, otherwise x86 cannot know how to size it:
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* Error: unsupported syntax for `movzx' */
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movzx $0, %eax
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/* Operands have the same size. Fist must be larger.
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* Error: unsupported syntax for `movzx' */
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movzx %al, %al
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#endif
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LKMC_EPILOGUE
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