What's the difference between MOV, MOVZ, MOVN and MOVK in ARMv8 assembly?
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I was using a disassembler when I came across MOVZ and was a bit confused, since I had only used MOV before.
The ARMv8 ISA manual explains of course all the details, and that MOV is an alias for the other three depending on the context, but maybe someone can provide some rationale here, and give concrete examples to speedup the learning process.
arm armv8
asked Nov 12 at 18:34
Ciro Santilli
50714
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I was using a disassembler when I came across MOVZ and was a bit confused, since I had only used MOV before.
The ARMv8 ISA manual explains of course all the details, and that MOV is an alias for the other three depending on the context, but maybe someone can provide some rationale here, and give concrete examples to speedup the learning process.
arm armv8
asked Nov 12 at 18:34
Ciro Santilli
50714
What's your manual? infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0802a/… describes the differences in quite a short way, so I'm kind of confused what you are looking for.
– domen
Nov 13 at 8:19
@domen developer.arm.com/docs/ddi0487/latest/… seems a bit better. But I'm guessing it must be there somewhere.
– Ciro Santilli
Nov 13 at 9:42
I think I don't understand your question.movz - Move shifted 16-bit immediate to register.Then:movn - Move inverse of shifted 16-bit immediate to register.How much shorter do you want it?
– domen
Nov 13 at 10:00
@domen one could explain the encoding of immediate to new users I think, and show why we need the three encoding types.
– Ciro Santilli
Nov 13 at 10:36
@Close voters: can you explain rationale? There are thousands of assembly questions on SO, so it seems like a well established topic. You should likely open a meta post instead to decide once and for all for all of them instead of close-voting one by one.
– Ciro Santilli
Nov 16 at 7:01
|
show 2 more comments
up vote
0
down vote
favorite
up vote
0
down vote
favorite
I was using a disassembler when I came across MOVZ and was a bit confused, since I had only used MOV before.
The ARMv8 ISA manual explains of course all the details, and that MOV is an alias for the other three depending on the context, but maybe someone can provide some rationale here, and give concrete examples to speedup the learning process.
arm armv8
asked Nov 12 at 18:34
Ciro Santilli
50714
I was using a disassembler when I came across MOVZ and was a bit confused, since I had only used MOV before.
The ARMv8 ISA manual explains of course all the details, and that MOV is an alias for the other three depending on the context, but maybe someone can provide some rationale here, and give concrete examples to speedup the learning process.
arm armv8
arm armv8
asked Nov 12 at 18:34
Ciro Santilli
50714
asked Nov 12 at 18:34
Ciro Santilli
50714
asked Nov 12 at 18:34
Ciro Santilli
50714
asked Nov 12 at 18:34
Ciro Santilli
50714
asked Nov 12 at 18:34
Ciro Santilli
50714
50714
What's your manual? infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0802a/… describes the differences in quite a short way, so I'm kind of confused what you are looking for.
– domen
Nov 13 at 8:19
@domen developer.arm.com/docs/ddi0487/latest/… seems a bit better. But I'm guessing it must be there somewhere.
– Ciro Santilli
Nov 13 at 9:42
I think I don't understand your question.movz - Move shifted 16-bit immediate to register.Then:movn - Move inverse of shifted 16-bit immediate to register.How much shorter do you want it?
– domen
Nov 13 at 10:00
@domen one could explain the encoding of immediate to new users I think, and show why we need the three encoding types.
– Ciro Santilli
Nov 13 at 10:36
@Close voters: can you explain rationale? There are thousands of assembly questions on SO, so it seems like a well established topic. You should likely open a meta post instead to decide once and for all for all of them instead of close-voting one by one.
– Ciro Santilli
Nov 16 at 7:01
|
show 2 more comments
What's your manual? infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0802a/… describes the differences in quite a short way, so I'm kind of confused what you are looking for.
– domen
Nov 13 at 8:19
@domen developer.arm.com/docs/ddi0487/latest/… seems a bit better. But I'm guessing it must be there somewhere.
– Ciro Santilli
Nov 13 at 9:42
I think I don't understand your question.movz - Move shifted 16-bit immediate to register.Then:movn - Move inverse of shifted 16-bit immediate to register.How much shorter do you want it?
– domen
Nov 13 at 10:00
@domen one could explain the encoding of immediate to new users I think, and show why we need the three encoding types.
– Ciro Santilli
Nov 13 at 10:36
@Close voters: can you explain rationale? There are thousands of assembly questions on SO, so it seems like a well established topic. You should likely open a meta post instead to decide once and for all for all of them instead of close-voting one by one.
– Ciro Santilli
Nov 16 at 7:01
What's your manual? infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0802a/… describes the differences in quite a short way, so I'm kind of confused what you are looking for.
– domen
Nov 13 at 8:19
What's your manual? infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0802a/… describes the differences in quite a short way, so I'm kind of confused what you are looking for.
– domen
Nov 13 at 8:19
@domen developer.arm.com/docs/ddi0487/latest/… seems a bit better. But I'm guessing it must be there somewhere.
– Ciro Santilli
Nov 13 at 9:42
@domen developer.arm.com/docs/ddi0487/latest/… seems a bit better. But I'm guessing it must be there somewhere.
– Ciro Santilli
Nov 13 at 9:42
I think I don't understand your question.
movz - Move shifted 16-bit immediate to register. Then: movn - Move inverse of shifted 16-bit immediate to register. How much shorter do you want it?– domen
Nov 13 at 10:00
I think I don't understand your question.
movz - Move shifted 16-bit immediate to register. Then: movn - Move inverse of shifted 16-bit immediate to register. How much shorter do you want it?– domen
Nov 13 at 10:00
@domen one could explain the encoding of immediate to new users I think, and show why we need the three encoding types.
– Ciro Santilli
Nov 13 at 10:36
@domen one could explain the encoding of immediate to new users I think, and show why we need the three encoding types.
– Ciro Santilli
Nov 13 at 10:36
@Close voters: can you explain rationale? There are thousands of assembly questions on SO, so it seems like a well established topic. You should likely open a meta post instead to decide once and for all for all of them instead of close-voting one by one.
– Ciro Santilli
Nov 16 at 7:01
@Close voters: can you explain rationale? There are thousands of assembly questions on SO, so it seems like a well established topic. You should likely open a meta post instead to decide once and for all for all of them instead of close-voting one by one.
– Ciro Santilli
Nov 16 at 7:01
|
show 2 more comments
1 Answer
1
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votes
up vote
2
down vote
MOV
This instruction can take many forms, depending on the value needed to be moved. Changes if the value is an register or an immediate. If it is in a register then it produces an ORR instruction (ORR <Xd>, XZR, <Wm>)* and if it is using the SP (Stack Pointer) it produces an ADD (ADD <Xd|XSP>, <Xn|XSP>, #0)*. If you are moving an immediate, then is using one of the MOVZ, MOVK or MOVN instruction.
*These are the 64-bit prototypes.
MOVZ and MOVK
These two are sometimes used one after the other. And they are used to move immediates.
MOVZ moves an immediate value (16-bit value) to a register, and all the other bits outside the immediate value are set to Zero. The immediate can be shift to the left 0, 16, 32 or 48. MOVK moves and immediate value but leaves the other bits of the register untouched. For example, let's say you need to move this value 0x7fb7fb1f88 to register X0. First, you will move the first 16 bits (bit 0 to 15) with a MOVZ instruction, so the rest of the register is set to zero. And then you will move the second 16 bits (bit 16 to 31) with a MOVK instruction, so the value moved before (the first 16 bits) remains in the register, and you do the same with the other resting bits.
instruction value of x0
mov x0, #0x1f88 | 0x1f88
movk x0, #0xb7fb, lsl #16 | 0xb7fb1f88
movk x0, #0x7f, lsl #32 | 0x7fb7fb1f88
MOVN
MOVN is usually used for moving bitmasks, let's say you want to move the bitmask 0xffffffff0000ffff to x0, then you will move 0xffff shift to the left 16, that will make the value 0x00000000fffff0000, but if you negate this value it becomes 0xffffffff0000ffff.
Here is an example:
instruction value of x0
MOVN x0, 0xFFFF, lsl 16 | 0xffffffff0000ffff
answered Nov 13 at 11:50
Guillermo
36626
add a comment |
1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
2
down vote
MOV
This instruction can take many forms, depending on the value needed to be moved. Changes if the value is an register or an immediate. If it is in a register then it produces an ORR instruction (ORR <Xd>, XZR, <Wm>)* and if it is using the SP (Stack Pointer) it produces an ADD (ADD <Xd|XSP>, <Xn|XSP>, #0)*. If you are moving an immediate, then is using one of the MOVZ, MOVK or MOVN instruction.
*These are the 64-bit prototypes.
MOVZ and MOVK
These two are sometimes used one after the other. And they are used to move immediates.
MOVZ moves an immediate value (16-bit value) to a register, and all the other bits outside the immediate value are set to Zero. The immediate can be shift to the left 0, 16, 32 or 48. MOVK moves and immediate value but leaves the other bits of the register untouched. For example, let's say you need to move this value 0x7fb7fb1f88 to register X0. First, you will move the first 16 bits (bit 0 to 15) with a MOVZ instruction, so the rest of the register is set to zero. And then you will move the second 16 bits (bit 16 to 31) with a MOVK instruction, so the value moved before (the first 16 bits) remains in the register, and you do the same with the other resting bits.
instruction value of x0
mov x0, #0x1f88 | 0x1f88
movk x0, #0xb7fb, lsl #16 | 0xb7fb1f88
movk x0, #0x7f, lsl #32 | 0x7fb7fb1f88
MOVN
MOVN is usually used for moving bitmasks, let's say you want to move the bitmask 0xffffffff0000ffff to x0, then you will move 0xffff shift to the left 16, that will make the value 0x00000000fffff0000, but if you negate this value it becomes 0xffffffff0000ffff.
Here is an example:
instruction value of x0
MOVN x0, 0xFFFF, lsl 16 | 0xffffffff0000ffff
answered Nov 13 at 11:50
Guillermo
36626
add a comment |
up vote
2
down vote
MOV
This instruction can take many forms, depending on the value needed to be moved. Changes if the value is an register or an immediate. If it is in a register then it produces an ORR instruction (ORR <Xd>, XZR, <Wm>)* and if it is using the SP (Stack Pointer) it produces an ADD (ADD <Xd|XSP>, <Xn|XSP>, #0)*. If you are moving an immediate, then is using one of the MOVZ, MOVK or MOVN instruction.
*These are the 64-bit prototypes.
MOVZ and MOVK
These two are sometimes used one after the other. And they are used to move immediates.
MOVZ moves an immediate value (16-bit value) to a register, and all the other bits outside the immediate value are set to Zero. The immediate can be shift to the left 0, 16, 32 or 48. MOVK moves and immediate value but leaves the other bits of the register untouched. For example, let's say you need to move this value 0x7fb7fb1f88 to register X0. First, you will move the first 16 bits (bit 0 to 15) with a MOVZ instruction, so the rest of the register is set to zero. And then you will move the second 16 bits (bit 16 to 31) with a MOVK instruction, so the value moved before (the first 16 bits) remains in the register, and you do the same with the other resting bits.
instruction value of x0
mov x0, #0x1f88 | 0x1f88
movk x0, #0xb7fb, lsl #16 | 0xb7fb1f88
movk x0, #0x7f, lsl #32 | 0x7fb7fb1f88
MOVN
MOVN is usually used for moving bitmasks, let's say you want to move the bitmask 0xffffffff0000ffff to x0, then you will move 0xffff shift to the left 16, that will make the value 0x00000000fffff0000, but if you negate this value it becomes 0xffffffff0000ffff.
Here is an example:
instruction value of x0
MOVN x0, 0xFFFF, lsl 16 | 0xffffffff0000ffff
answered Nov 13 at 11:50
Guillermo
36626
add a comment |
up vote
2
down vote
up vote
2
down vote
MOV
This instruction can take many forms, depending on the value needed to be moved. Changes if the value is an register or an immediate. If it is in a register then it produces an ORR instruction (ORR <Xd>, XZR, <Wm>)* and if it is using the SP (Stack Pointer) it produces an ADD (ADD <Xd|XSP>, <Xn|XSP>, #0)*. If you are moving an immediate, then is using one of the MOVZ, MOVK or MOVN instruction.
*These are the 64-bit prototypes.
MOVZ and MOVK
These two are sometimes used one after the other. And they are used to move immediates.
MOVZ moves an immediate value (16-bit value) to a register, and all the other bits outside the immediate value are set to Zero. The immediate can be shift to the left 0, 16, 32 or 48. MOVK moves and immediate value but leaves the other bits of the register untouched. For example, let's say you need to move this value 0x7fb7fb1f88 to register X0. First, you will move the first 16 bits (bit 0 to 15) with a MOVZ instruction, so the rest of the register is set to zero. And then you will move the second 16 bits (bit 16 to 31) with a MOVK instruction, so the value moved before (the first 16 bits) remains in the register, and you do the same with the other resting bits.
instruction value of x0
mov x0, #0x1f88 | 0x1f88
movk x0, #0xb7fb, lsl #16 | 0xb7fb1f88
movk x0, #0x7f, lsl #32 | 0x7fb7fb1f88
MOVN
MOVN is usually used for moving bitmasks, let's say you want to move the bitmask 0xffffffff0000ffff to x0, then you will move 0xffff shift to the left 16, that will make the value 0x00000000fffff0000, but if you negate this value it becomes 0xffffffff0000ffff.
Here is an example:
instruction value of x0
MOVN x0, 0xFFFF, lsl 16 | 0xffffffff0000ffff
answered Nov 13 at 11:50
Guillermo
36626
MOV
This instruction can take many forms, depending on the value needed to be moved. Changes if the value is an register or an immediate. If it is in a register then it produces an ORR instruction (ORR <Xd>, XZR, <Wm>)* and if it is using the SP (Stack Pointer) it produces an ADD (ADD <Xd|XSP>, <Xn|XSP>, #0)*. If you are moving an immediate, then is using one of the MOVZ, MOVK or MOVN instruction.
*These are the 64-bit prototypes.
MOVZ and MOVK
These two are sometimes used one after the other. And they are used to move immediates.
MOVZ moves an immediate value (16-bit value) to a register, and all the other bits outside the immediate value are set to Zero. The immediate can be shift to the left 0, 16, 32 or 48. MOVK moves and immediate value but leaves the other bits of the register untouched. For example, let's say you need to move this value 0x7fb7fb1f88 to register X0. First, you will move the first 16 bits (bit 0 to 15) with a MOVZ instruction, so the rest of the register is set to zero. And then you will move the second 16 bits (bit 16 to 31) with a MOVK instruction, so the value moved before (the first 16 bits) remains in the register, and you do the same with the other resting bits.
instruction value of x0
mov x0, #0x1f88 | 0x1f88
movk x0, #0xb7fb, lsl #16 | 0xb7fb1f88
movk x0, #0x7f, lsl #32 | 0x7fb7fb1f88
MOVN
MOVN is usually used for moving bitmasks, let's say you want to move the bitmask 0xffffffff0000ffff to x0, then you will move 0xffff shift to the left 16, that will make the value 0x00000000fffff0000, but if you negate this value it becomes 0xffffffff0000ffff.
Here is an example:
instruction value of x0
MOVN x0, 0xFFFF, lsl 16 | 0xffffffff0000ffff
answered Nov 13 at 11:50
Guillermo
36626
answered Nov 13 at 11:50
Guillermo
36626
answered Nov 13 at 11:50
Guillermo
36626
answered Nov 13 at 11:50
Guillermo
36626
36626
add a comment |
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What's your manual? infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0802a/… describes the differences in quite a short way, so I'm kind of confused what you are looking for.
– domen
Nov 13 at 8:19
@domen developer.arm.com/docs/ddi0487/latest/… seems a bit better. But I'm guessing it must be there somewhere.
– Ciro Santilli
Nov 13 at 9:42
I think I don't understand your question.
movz - Move shifted 16-bit immediate to register.Then:movn - Move inverse of shifted 16-bit immediate to register.How much shorter do you want it?– domen
Nov 13 at 10:00
@domen one could explain the encoding of immediate to new users I think, and show why we need the three encoding types.
– Ciro Santilli
Nov 13 at 10:36
@Close voters: can you explain rationale? There are thousands of assembly questions on SO, so it seems like a well established topic. You should likely open a meta post instead to decide once and for all for all of them instead of close-voting one by one.
– Ciro Santilli
Nov 16 at 7:01