Eax vs rax

However, it could also possibly cause problems too. The new registers also got their “narrow” versions. This is done because the eax register is 4 bytes wide which make up a long. – fpmurphy. eax, ebx, ecx and so on are actually registers, which can be seen as "hardware" variables, somewhat similar to higher level-language's variables. broadcasts the sign bit of eax into every bit of edx. Sep 23, 2019 · Orbi has advantage over regular mesh because of dedicated backhaul, allowing for higher performance. Jun 24, 2011 · Ptrace needs to be able to read both all registers state before syscall and the return value of syscall; but the return value is written to %eax. A router like the RAX80/120/200 will give better “single” unit coverage and better overall speeds at close to medium ranges. EBX: "Extended Base" - often used as a pointer to data in the data segment of memory. All 3 give completely identical results for registers, flags, opcode length, latency, throughput. Curiously, you can write a 64-bit value into rax, then read off the low 32 bits from eax, or the low 16 bitx from ax, or the low 8 bits from al Nov 18, 2009 · x64 extends x64's 8 general-purpose registers to be 64-bit, and adds 8 new 64-bit registers. It should be: syscall cmp 0xfffffffffffff000, %rax jbe . There are also the lower parts of those registers in case of you don't know yet. al and ah are the 8-bit, "char" size parts of the register. If you include slight differences like that as redundant, or even instructions that run on different execution ports, there are lots of ways to do some things. By design, strcpy can return either -1,0 or 1 in EAX with 0 indicating both strings match. then lea rax, [rbp-50h] would result in 5. Registers can be used in your software directly with instructions such as mov, add or cmp. But add %dl, (%rax) is an RMW on (%rax), so the dl data isn't needed until a load from (%rax) has that data ready. This is happening because you're returning zero. to indicate operand size 8 Jun 25, 2021 · Whenever I run a pointer scan I don't get any results, so I was going to use AOB to just NOP the decrease, but the health value gets passed between RAX and EAX and it crashes the game; because it's no longer passing values between mem and registers (I'm guessing). It's not clear why it is happening here. May 15, 2016 · Now, leal is used for address assignment. If the suffix is not specified, and there are no memory operands for the instruction, GAS infers the operand size from the size of the destination register operand. It was added in 1985 during the transition to 32-bit processors. However, unless I am mistaken, %eax is a 32-bit register. On AMD Bulldozer-family, it's 4c or 6c latency, and one per 2c or one per 4c throughput. 1 on Sandybridge-family, so disp32 + index*2 is faster than disp8 + base + index*1 on SnB-family, i. And yet for testing if 0, if not zero, or if signed, some compilers will use test eax,eax while some use or eax,eax, and I was Jan 13, 2014 · If you only use al for an 8-bit value, it leaves ah free for a second one. g i r rdi rsi, i r: print all register except floating point & vector register (xmm, ymm, zmm). Jan 19, 2014 · mov rax, 1 ; #1 add rax, 2 ; #2 mov rax, 3 ; #3 add rax, 4 ; #4 The CPU can perform instructions #1 and #3 as soon as they're decoded, since they require no dependencies to be fulfilled (and run over the old value in rax). The machine command will copy the content of %edx to the address given by %rbp + 4 * %rax - 0x80. %eax is the 32 bit one, and %ax would be 16 bits. Pushes the contents of the general-purpose registers onto the stack. It’s a mess, but it is the most widely used ISA in the world today. ). fast food restaurant chain specializing in roast beef sandwiches. – Feb 11, 2019 · The CDQE instruction sign-extends a DWORD (32-bit value) in the EAX register to a QWORD (64-bit value) in the RAX register. If you do this with any other 32-bit register, it will clear the top 32 bits of the corresponding 64-bit register, but not in the "eax, eax" form. Similarly, in the 64-bit version, the 'E' is replaced with an 'R' ( register ), so the 64-bit version of 'EAX' is called 'RAX'. Not to be confused with cdqe, the 64-bit instruction that is a more compact form of movsxd rax, eax. And that, folks, was a quick history of x86 accumulator! From an 8-bit A of 8008, to 16-bit AX of 8086, to 32-bit EAX of 80386, to 64-bit RAX. S. Note that this is exactly the value of ecx. e. . In x86 processors registers are 32 bits long and the "accumulator register" (RAX in amd64) is here named EAX. To be sure for what the hell it is done we need to see what will happen to %rdx later. states in the 1980s and falling to fewer than 20 locations on more than one occasion. imul r, r/m and imul r, r/m, imm are both 3 cycle latency, one per 1c throughput on Intel SnB-family and AMD Ryzen, even for 64bit operand size. then modify AX ( not RAX ) to something you like ( and something that will fit in a WORD ) ie: mov AX , 01 // AX = 2 bytes ) ps. As complete 32-bit data registers: EAX, EBX, ECX, EDX. Jan 4, 2022 · syscall cmp $0, %rax jg . Divides unsigned the value in the AX, DX:AX, EDX:EAX, or RDX:RAX registers (dividend) by the source operand (divisor) and stores the result in the AX (AH:AL), DX:AX, EDX:EAX, or RDX:RAX registers. Because it its the address of the array, and ebx is the index (mostlikely 8 or 2, depending on if it holds integer or bytes). Thus, after movl $-1, %eax, the %rax register has value 0x0000'0000'FFFF'FFFF. eax vs. This operation cannot be done at once (as in mov dword [esp + 4], dword [eax], cannot have two memory references in the same instruction), so it is split in two Oct 24, 2019 · If you're wondering why not movzbw (%rdi), %ax for short, that's because writing to 8-bit and 16-bit partial registers has to merge with the previous high bytes. %ah refers to the high 8 bits of the 16 bits in the register, and %al refers to the lower end. Jul 30, 2022 · Depending on placement and distances either the RAX/EAX system would work or the Orbi system would work for most of the internal home coverage. Take R15, for example: ⁂. Notice that it's not dereferenced as a byte. reg). E. Jan 1, 2024 · For example, 'EAX' is the accumulator register as a 32-bit value. This is because there are no encodings to access those parts in any instruction. They're original back to 1972. x86 is a poorly-designed ISA. So my question is: I thought x64 used RAX etc and x86 used EAX, but it appears x86 specifies register sizes using prefix bytes. Four 32-bit data registers are used for arithmetic, logical, and other operations. •%raxstores the return value •%rdistores the first parameter to a function Sep 9, 2009 · xor eax, eax is a faster way of setting eax to zero. The only other difference is that the cmp instruction will properly set the obscure AF flag, while the test instruction leaves the contents of that flag undefined. And then you can jump using an indirect jump, e. Note that you don't need any actual instructions -- the constraints tell gcc that after doing nothing, the value rax will be in rax and the %eax for syscall_number. Dec 9, 2020 · The compiler could have moved this load earlier as well, but chose not to. L1. In this case, are -0x14(%rsbp) and -0x20(%rbp) both memory operands and We would like to show you a description here but the site won’t allow us. TEST EAX,EAX tests whether EAX is zero or not and sets or unsets the ZF bit. I don't know what kind of assembly is that, i'm used to right to left mov, but it seems to be opposite in your example. Mar 25, 2011 · Gdb commands: i r <register_name>: print a single register, e. g. Gotta be careful there. Apr 1, 2011 · mov eax, 0x87654321 will make rax equal 0x0000000087654321, and mov rax, 0x87654321 will make rax equal 0xffffffff87654321. And the "value of the pointer needed" is C419588. Oct 19, 2019 · movzwl reads a word (16 bits) from the source, zero-extends it to a long (32 bits), and writes it into the destination register. If you want to set the low bits without changing the high bits, you can do a trick like: // sets eax to ebx without changing rax[32. MOV sets EAX = the value from memory at that address. Compares the first source operand with the second source operand and sets the status flags in the EFLAGS register according to the results. . For e. The MOVZX instruction zero-extends the source to the destination. Just because it is popular does not mean it’s good. most of the mainstream x86 CPUs we care about optimizing for. mov eax, 0 ; doesn't touch FLAGS, but not 2. 처음 네 개의 16비트 레지스터 (ax, cx, dx, bx)는 두 개의 8비트 레지스터로 각각 접근할 수 있다. Otherwise, the destination operand is loaded into the AL, AX, EAX or RAX register. The kernel does not know what your Sep 29, 2020 · LaC is right. (mov eax,0 isn't totally redundant, because it doesn't affect flags. The in instruction is doing stuff with I/O ports. •%raxstores the return value •%rdistores the first parameter to a function Nov 14, 2012 · ecx = C419588. Feb 18, 2018 · To efficiently do x = x*10 + 1, it's probably optimal to use. It assigns the above address to %eax, hence you get %eax := %edx * 5. Symbol () means the address of the register. Lower halves of the 32-bit registers can be used as four 16-bit data registers: AX, BX, CX and DX. I took following snippet from the Linux Assembly Tutorial but I'm doubtful about this. The question is this: When we manipulate %rax after moving $1 into %eax, are we sure that the Different names (e. answered Nov 8, 2021 at 20:25. x86アーキテクチャには通常、汎用レジスタがeax、ebx、ecx、edxなどの32ビットレジスタとして存在します。 一方、x64アーキテクチャでは、より多くの汎用レジスタ（RAX、RBX、RCX、RDXなど）が64ビットレジスタとして使用されます。 Dec 9, 2022 · 1 3. (The upper half of EAX isn't directly accessible as a 16-bit register; you can shift or rotate EAX if you want to get at it. rax is used as running sum and after the sumLoop which calculates the sum, I assign the value of it to rdx which is May 17, 2014 · The question is specifically about the difference between the specific cases test eax,eax, or eax,eax and and eax,eax. On the other hand, mov rax, [rbp-50h] would most probable crash your application, as it would try to read the content of the address 5 and put it into rax. r14 vs lr on ARM) and smaller views of a register (e. UPDATE: Thanks to R. The action of this instruction depends on the operand size Mar 15, 2021 · 1. The comparison is performed by subtracting the second operand from the first operand and then setting the status flags in the same manner as the SUB instruction. %ebx, %ecx, %edx, %esi, %edi, %ebp are used for passing 6 parameters to system calls. ) when register shifting and bitwise operations rax is the 64-bit, "long" size register. But in the case of cmp eax,0 the AF will always be cleared regardless of the value of eax Assume that rpb has a value of 55h (Assembler syntax). The registers are stored on the stack in the following order: EAX, ECX, EDX, EBX, ESP (original value), EBP, ESI, and EDI (if the current operand-size attribute is 32) and AX, CX, DX, BX, SP (original value), BP, SI, and DI (if the operand-size attribute is 16). After the xor instruction, rax would contain 0, because XORing a value with itself results in 0. And registers almost always counted from zero, so RBX should be R3, and AX, CX, DX would be R0, R1, R2 respectively. Loading ax vs. jmp rax (or whatever it is in AT&T syntax). ) x86-64 CPUs extend the integer registers to 64-bit: RAX is the full 64-bit value, with These registers could be treated as having two separate 16 bit components (least significant 16 bits accessed using the 16 bit name such as EAX -> AX, EBX -> BX, etc. Aug 31, 2021 · This program is used to calculate the sum and average of all the elements in arr. You'll have to use indirect instruction sequences if you're interested in doing that. LEA sets EAX = the address. – Carl Norum Jan 5, 2022 · Thus, if rax is 0x0123456789abcedf then eax is 0x89abcdef, ax is 0xcdef, al is 0xef, and ah is 0xcd. Subregisters cannot be renamed, which cramps the processor's ability to parallelize operations. (Registers don't have addresses, but C memcpy only works by reference; C isn't assembly language). Then original eax, used before syscall will be lost. This guide should give you enough background to read and understand (most) of the 64bit x86 assembly that gcc is likely to produce. Sep 24, 2010 · __int64 rax;}; // eax and rax share same register, eax is low part of that register *** however some operations on eax bung up padd (as intended) This mapping is like al is to ax, al is to eax, al is to rax ax is to eax, ax is to rax eax is to rax with rax though there are some rules as to what happens to upper bits of 64-bit register (sign The ADD instruction performs integer addition. RAX EAX AX Registers (x86-64 architecture) AL 63 31 15 7 0 RBX EBX BX BL RCX ECX CX CL RDX EDX DX DL General purpose registers: 17. rax is the 64-bit, "long" size register. So in this case rsi seems to be one of Thus, after movl $-1, %eax, the %rax register has value 0x0000'0000'FFFF'FFFF. eax is the value written into this variable. The company has been through many iterations, declaring bankruptcy more than once, rising to as many as 504 locations in 38 U. O t h e rs, su ch a s m ovs Sep 18, 2016 · The test instruction always clears OF and CF, but that's also what cmp against zero does. It evaluates the result for both signed and unsigned integer operands and sets the OF and CF flags to indicate a carry (overflow) in the signed or unsigned result, respectively. mov $0x0, %eax # write return value to %rax add $0x10, %rsp # deallocate stack frame retq # return from current function, resume caller It was added in 1979, but is used in DOS or BIOS code to this day. movslq reads a long (32 bits) from the source, sign extends it to a qword (64 bits, replicating bit 31 into bits 63:32), and writes it into the destination register. You can fetch the address from the RAX is a 64 bits register (maximum value is 2 64-1) and only exists in amd64 (or x86_64) processors. 즉, 'eax'의 64비트 버전은 'rax'가 된다. Where RBX is a uint64_t holding the value 10. Dec 13, 2013 · 4. Mar 30, 2010 · The following is a brief explanation of what each of the x86 general-purpose registers stands for: EAX: "Extended Accumulator" - used for arithmetic and logical operations, as well as for storing return values from functions. xor eax,eax. But compilers just use mov unless optimizing for size over speed. The SF flag indicates the sign of the signed result. The new registers are named r8 through r15. The same applies to the other cases. That's an 8-byte store to memory, like C memcpy(&DigitSpace, &local_var, 8). so 'movl 8 (%ebp), %eax' means set %eax with the address of the %ebp. At the end the leaq command will multiply %rax by 4 and store it into %rdx. If the two values are equal, the second operand (source operand) is loaded into the destination operand. These 32-bit registers can be used in three ways −. Here's a reference that seems to explain it in detail. Like C++ variables, registers are actually available in several sizes: rax is the 64-bit, "long" size register. The source operand can be an immediate, a register, or a memory location; the destination operand can be a register or a memory location. eax is the 32-bit, "int" size register. Explicit registers are specified as string literals (e. 3 cycles vs. Note that explicit registers treat register aliases (e. Description ¶. 11 1. Well, read it a few times. Jul 9, 2018 · It is impossible to access the higher parts of the EAX and RAX registers, or of any other 32 and 64-bit registers, directly. The leading e stands for e xtended and means that your register is 32 bits wide. Aug 4, 2023 · In order to achieve maximum compatibility, on 64-bit platforms Linux clips input and output of system calls using the interrupt method. The options are mov eax, 1 (5 bytes) to set RAX=1 via implicit zero extension, or push 1 / pop rax (3 bytes), or xor eax,eax / inc eax (4 bytes). g i r rax, i r eax. 64] xor ebx, eax xor rax, rbx Not perfect - it changes ebx (but you can get the low bits Jun 29, 2013 · In this case, the %rax register is a 64 bit register. Apr 7, 2016 · div / idiv: divides edx:eax by the src. There's no form of div / idiv that ignores edx in the input. Having the RAX address ready early is more valuable than the DL data because the address is being used for another load, not ALU -> store. It was added in 2003 during the transition to 64-bit processors. Are you asking about which byte will Sep 14, 2019 · Case 1 : You are moving the value at address specified by register rsp to the register eax. movb - move byte. RAX register is available only in 64-bit mode. and great LXR, I did a full search of orig_eax in linux 0. 10 Data Sizes Registers are 64 bits, but we can refer to just the lower [32, 16 or 8] bits of each register by different names. answered Nov 13, 2012 at 10:37. 5gb port. eax vs rax ) as equivalent to the base register. 비슷하게, 64비트 버전에서는 'e' 대신 'r'을 사용한다. Next %eax is extended to 64bit rax by the machine command cltq. Dec 15, 2010 · Actually, opcode 0x90 (corresponding to xchg %eax, %eax in 32-bit code) is a dedicated NOP on x86-64. Here we're loading the same constant 0x12 into all the different sizes of eax: Compares the value in the AL, AX, EAX, or RAX register with the first operand (destination operand). lea eax, [rax + rax*4] ; x*=5 lea eax, [1 + rax*2] ; x = x*2 + 1 3-component LEA has higher latency on modern Intel CPUs, e. I'm getting into the first struggles of teaching myself assembly, and I came across an example in a text that left me with a question: Consider the following code: (Assume %rdx has been loaded with an arbitrary variable) movl $1, %eax. Take a look here to get a better understanding for the AT&T syntax. Moreover, further down in the code, it actually uses the 64-bit register %rax to do the iterating, which never gets initialized outside of xorl %eax %eax, which would For example, we use XOR to zero out the rax register: xor eax, eax. i r <register_name_1> <register_name_2> : print multiple registers, e. I'm in the habit of using this register size, since they also work in 32 bit mode, although I should probably use the longer rax Mar 20, 2020 · So R in RAX stood for register, and was a way to unify the naming to be more consistent with the new R8 – R15 registers. Here, the source operand (in a general-purpose register or memory location) is multiplied by the value in the AL, AX, EAX, or RAX register (depending on the operand size) and the product (twice the size of the input operand) is stored in the AX, DX:AX, EDX:EAX, or RDX:RAX registers, respectively. sub eax,eax to zero rax vs. 7. Basically reading a word of data from the port specified dx in and storing it in al. May 15, 2022 · ie: press <CTRL>a on that code line. rax) refer to different parts of the same register For instance, consider an instruction located at (starting-point + 0x80) that loads a variable g located at (starting-point + 0x1000) into %rax. This is slightly more efficient than using rax directly: Rax Roast Beef is a regional U. mov eax,[edx] does exactly the reverse, reads a value stored from the memory, from the address Jun 20, 2016 · That's right, modern x86 CPUs (especially Intel) have very high performance multipliers. then press <CTRL><SHIFT>a to create an injection point. ) or four 8 bit registers (least significant 16 bits accessed as two 8 bit registers such as EAX -> AH and AL, EBX -> BH and BL, etc. If you know about C unions I can provide a snippet of Jul 14, 2015 · In addition, unlike where we set x to 0, the mov instruction as shown in GAS syntax does not have a suffix. Dec 24, 2012 · The other commonly used assembly syntax for x86 is AT&T, but as Intel and AT&T syntaxes look very different, they are easy to distinguish. Additionally, instruction #2 can be performed in parallel right afterwards, as each depends only on the preceding instruction. So AX is composed of AH:AL halves, and is itself the low half of EAX. The return value is in %eax. Feb 3, 2012 · The real encoded order is AX, CX, DX, BX (See Why are first four x86 GPRs named in such unintuitive order? ). mov $0x0, %eax # write return value to %rax add $0x10, %rsp # deallocate stack frame retq # return from currently executing function, resume caller eax/rax is zeroed at start, and later is used as a counter for i, and edi seems to have n value here. •%rax stores the return value •%rdi stores the first parameter to a function e xa mp l e , mo vi n g a q u a d wo rd f ro m % rax to % rbx re su l t s i n t h e i n st ru ct i o n m ovq %rax, %rbx . cdq sign-extends eax into edx:eax, i. And %eax is the value of that address. EAX is the register used by IA32 calling conventions to either return an interger value or a memory address to the calling routine. quotient in eax, remainder in edx. So it seems to me that this should actually be xorq %rax, %rax, particularly since this is holding a 64-bit long int. May 12, 2017 · Also, in 64-bit registers, too, we can see in any low-level debugger such as Windbg that the right-most bits are still referred to by the same name as that of the 64-bit register except the name starts with an E. Lower and higher halves of the above-mentioned four 16 Jun 10, 2016 · Yes, this is one of many redundancies in x86 assembly language. "eax") while register classes are specified as identifiers (e. S o me i n st ru ct i o n s, l i ke r et , d o n o t u se su f f i xe s b e ca u se t h e re i s n o n e e d . Most people remember the restaurant at this time and the “endless salad and dessert bar” that came with your meal. It was added in 1985 during the transition to 32-bit processors with the 80386 CPU. rax may offer memory bandwidth advantages. 1 Kudo. AH is the bits 8 through 15 (zero-based), the top half of AX. Thus, the difference is that the first is direct, the second indirect. i r a: print all register, include floating point & vector register (xmm, ymm, zmm). CPUID returns processor identification and feature information in the EAX, EBX, ECX, and EDX registers. vikas william. mov [edx],eax stores the value of eax in memory, to the address given in edx (in little-endian byte order). It seems %rax is holding the index to that array and %rbp - 0x80 is the base address. Tips for golfing in x86/x64 machine code points out that a 3-byte lea eax, [rdx+1] from another register of known value can be useful. subq %rdx, %rax. hmm eax == 32bits ax == 16bits ah|al == 8bits, it's always like this, x64 adds new registers, back in the 16 bit days we only had ax & al & ah then when 32 bit addressing came round it was added in a way that didn't really effect how you address the 16bit or 8bit registers, the new registers in x64 (64 bit registers that overlap, eax that overlaps ax, etc) start with an r so rax rbx and so on. Some VIA CPUs expose the internal RISC instructions and R0-R4 are also mapped directly to EAX/ECX/EDX/EBX as expected. 예를 들어, 'eax'는 32비트 값을 갖는 어큐뮬레이터 레지스터이다. This instruction operates the same in non-64-bit modes and 64-bit mode. ax vs. The address of a qword memory location is the address of its lowest-address byte. The 64-bit registers have names beginning with "r", so for example the 64-bit extension of eax is called rax. al is the low 8 bits, ah is the high 8 bits. All other registers (including EFLAGS) are preserved across the int $0x80. you don't even have to save AX (2 bytes) because it's not used later ( movzx eax, byte ptr [rcx+1a] ) -edit-- oh lol i didn Here, the source operand (in a general-purpose register or memory location) is multiplied by the value in the AL, AX, EAX, or RAX register (depending on the operand size) and the product (twice the size of the input operand) is stored in the AX, DX:AX, EDX:EAX, or RDX:RAX registers, respectively. %eax is the 32-bit sub-register within %rax. This is commonly seen, because the scaling factor scale can only be 1, 2, 4, 8, hence there is no way to multiply %edx by 5 directly. the right-most 32 bits of the RAX register in a 64-bit system is referred to as EAX. The same is true after movq $-1, %rax; addl $0, %eax! (The movq sets %rax to 0xFFFF'FFFF'FFFF'FFFF; the addl sets its upper 32 bits to zero. Defined by the owners as the “champagne of fast food”. The lower 32 bits, 16 bits, and 8 bits of each register are directly addressable in operands. It is done by a function called stats1. The name Rax did not come along until the early 1980s when it was the most popular. Two-operand form As you can see, whatever is in %esi will copied on the stack and then copied to %eax. If any one can show an example, it would be Performs a bitwise exclusive OR (XOR) operation on the destination (first) and source (second) operands and stores the result in the destination operand location. malloc_exit_ This is typical of UNIX system calls; they return -1 to indicate an error, and the thunk is responsible for updating errno, or whatever your c-bindings look like. malloc_exit_ Is not right. In part because x86-64 has preserved backwards compatibility with many previous architectures all the way back to the 16-bit integer-only 8086, many newer operations have been placed in their own register bank with their own operations. Similarly, if want to get %eax = %edx * 3, we have to do leal (%edx, %edx, 2), %eax. 16 Register Responsibilities Some registers take on special responsibilities during program execution. 5 Specifying an Offset The offset part of a memory address can be specified directly as a static value (called a displacement) or through an address computation made up of one or more of the following components: Feb 15, 2013 · Because I want the eax*4 to be in increments of bytes, not 32-bit words. It is also possible to address the first four registers (AX, CX, DX and BX) in their size of 16-bit as two 8-bit halves. In a non-PIE, the instruction might be written movq 0x400080, %rax (in compiler output, movq g, %rax ); but this relies on g having a fixed address. Nov 12, 2015 · xor edx, edx ; RDX = 0 ; small code-size alternative: cdq ; zero RDX if EAX is already zero ; SUB-OPTIMAL xor rax,rax ; waste of a REX prefix, and extra slow on Silvermont xor r10,r10 ; bad on Silvermont (not dep breaking), same as r10d on other CPUs because a REX prefix is still needed for r10d or r10. When callee finishes, it writes the return value (if any) to %rax, cleans up the stack, and use retq instruction to return control to the caller. In x64, any operation on a 32-bit register clears the top 32 bits of the corresponding 64-bit register too, so there's no need to use xor rax, rax which would necessitate an extra REX byte for encoding. Therefore, you should use movl which means move a long value. The right way to do this with gcc is with register contraints: uint64_t rax = 0, rbx = 0; __asm__("" : "=a"(rax), "=b"(rbx) ::); /* make rax and rbx take on the current values in those registers */. I can run two satellites however I turn down the power to 50%. For example, for the write system call, it grabs the file descriptor from ebx, a pointer to the buffer you want to write from ecx and the number of bytes you want to write from edx. e. r11 seems to be j counter, but with missing rest of code i'm just guessing here. Honestly the RAX200 is just an RAX80 with an extra 5Ghz band and a 2. Registers (x86-64 architecture) movq %rax, (%rbx) popq %rbx ret Use of %to indicate registers Use of q/l/w/bto indicate 64 / 32 / 16 / 8-bit operands Intel Syntax multstore: push rbx mov rbx, rdx call mult2@PLT mov QWORD PTR [rbx], rax pop rbx ret Register names are bare Use of QWORDetc. Writing a 32-bit register like EAX implicitly zero-extends into the full RAX, avoiding a false dependency on the old value of RAX or any ALU merging uop. Message 2 of 5. To save it, there is a orig_eax field. Nov 18, 2018 · From eax it grabs the number of the system call you want to execute and from the other registers it grabs additional data. About the why this would happen, it depends on the context. So, do the E and R stand for something? Sep 4, 2022 · The company started in Springfield Ohio in 1967 Under the name of Jax Roast Beef. For example, this could be used to load the value of [eax] on the stack, to use it as an argument for a function call. movw - move word (2 bytes). ) Modifying a 16- or 8-bit register name leaves all other bits of the register unchanged. Apr 17, 2019 · There are several ways to implement switch, but the most obvious one is to have an array/table of addresses of where to jump to and then just use an integer index into it to retrieve the corresponding to it address. 95. (However, two memory operands cannot be used Oct 31, 2015 · To quote the intel basic architecture manual: 3. For example, the same "0xb8" instruction that loads a 32-bit constant into eax can be used with a "0x66" prefix to load a 16-bit constant, or a "0x48" REX prefix to load a 64-bit constant. It breaks almost every rule of good ISA design. That means, for instance, you cannot pass, nor receive (complete) 64-bit address pointers on an x86-64 platform using the int $0x80 method, because the upper 32 bits of all arguments and the result are zeroed. Why I need to use eax instead of rax in line 16? In my case, I first assign the address of sum into rdx. Description ¶ . This instruction can be used with a LOCK prefix to allow the 16 Register Responsibilities Some registers take on special responsibilities during program execution. The source operand can be a general-purpose register or a memory location. I have a 5k sq ft home and most of the time just 1 router and satellite is sufficient. 1 The instruction’s output is dependent on the contents of the EAX register upon execution (in some cases, ECX as well). ny qz qx qw ku bd ie tt nz hv