X64 jmp

X64 jmp

Transfers program control to a different point in the instruction stream without recording return information. The destination target operand specifies the address of the instruction being jumped to. This operand can be an immediate value, a general-purpose register, or a memory location.

Near and Short Jumps. When executing a near jump, the processor jumps to the address within the current code segment that is specified with the target operand. The target operand specifies either an absolute offset that is an offset from the base of the code segment or a relative offset a signed displacement relative to the current.

JMP System Requirements

A near jump to a relative offset of 8-bits rel8 is referred to as a short jump. The CS register is not changed on near and short jumps. The operand-size attribute determines the size of the target operand 16 or 32 bits. Absolute offsets are loaded directly into the EIP register. If the operand-size attribute is 16, the upper two bytes of the EIP register are cleared, resulting in a maximum instruction pointer size of 16 bits. A relative offset rel8, rel16or rel32 is generally specified as a label in assembly code, but at the machine code level, it is encoded as a signed 8-,or bit immediate value.

This value is added to the value in the EIP register. When using relative offsets, the opcode for short vs. When executing a far jump in real-address or virtual mode, the processor jumps to the code segment and offset specified with the target operand. Here the target operand specifies an absolute far address either directly with a pointer ptr or ptr or indirectly with a memory location m or m With the pointer method, the segment and address of the called procedure is encoded in the instruction, using a 4-byte bit operand size or 6-byte bit operand size far address immediate.

With the indirect method, the target operand specifies a memory location that contains a 4-byte bit operand size or 6-byte bit operand size far address. If the operand-size attribute is 16, the upper two bytes of the EIP register are cleared. Far Jumps in Protected Mode.Wikipedia has related information at Control flow. Almost all programming languages have the ability to change the order in which statements are evaluated, and assembly is no exception.

The instruction pointer EIP register contains the address of the next instruction to be executed. To change the flow of control, the programmer must be able to modify the value of EIP. This is where control flow functions come in. Performs a bit-wise logical and on arg0 and arg1 the result of which we will refer to as commonBits and sets the ZF zeroSF sign and PF parity flags based on commonBits. CommonBits is then discarded.

x64 jmp

Performs a comparison operation between minuend and subtrahend. The comparison is performed by a signed subtraction of subtrahend from minuendthe results of which can be called difference. Difference is then discarded. If subtrahend is an immediate value it will be sign extended to the length of minuend. The jump instructions allow the programmer to indirectly set the value of the EIP register. The location passed as the argument is usually a label.

The first instruction executed after the jump is the instruction immediately following the label. All of the jump instructions, with the exception of jmpare conditional jumpsmeaning that program flow is diverted only if a condition is true. These instructions are often used after a comparison instruction see abovebut since many other instructions set flags, this order is not required.

Loads EIP with the specified address i. Loads EIP with the specified address, if operands of previous cmp instruction are equal. For example:. Loads EIP with the specified address, if operands of previous cmp instruction are not equal. Loads EIP with the specified address, if the minuend of the previous cmp instruction is greater than the second performs signed comparison. Loads EIP with the specified address, if the minuend of the of previous cmp instruction is greater than or equal to the subtrahend performs signed comparison.

Loads EIP with the specified address, if the minuend of the previous cmp instruction is greater than the subtrahend. That means, the following piece of code always jumps unless rbx is -1toobecause negative one is represented as all bits set in the two's complement.

That is the largest unsigned value a register can hold. Loads EIP with the specified address, if the minuend of previous cmp instruction is greater than or equal to the subtrahend. It loads EIP with the specified address, if the criterion is met. So either SF or OF can be set, but not both in order to satisfy this criterion. If we take the sub which is basically what a cmp does instruction as an example, we have:.

With respect to sub and cmp there are several cases that fulfill this criterion:. In the first case SF will be set but not OF and in second case OF will be set but not SF since the overflow will reset the most significant bit to zero and thus preventing SF being set.

Loads EIP with the specified address, if the minuend of previous cmp instruction is lesser than or equal to the subtrahend. See the jl section for a more detailed description of the criteria.It is a desktop statistical analysis program using exploratory graphics to promote statistical discovery.

JMP was released for Windows in and has been available for bit Linux since SAS's version 6. To understand the importance of a bit version of JMP, let us contemplate the purpose and history of statistical analysis. Ultimately, the purpose of statistics is to make sense out of too much information. For example, the only possible way to digest the results of the United States census data every ten years, with its dozens of measurements on million people, is by reducing it to statistical conclusions, such as the average household income by county and median age by city or neighborhood.

The problem is that there are hundreds and thousands of statistical measures—in fact, SAS has already spent 30 years extending and refining its analytical capabilities and doesn't see any end in sight. Learning what techniques to use for which real-world situations can take years, and developing the insights to proceed effectively from raw data to knowledge can take a lifetime.

Inspired by the way the Macintosh made desktop computing accessible to a whole new audience by introducing a graphical user interface, Sall realized he could make statistics accessible to a wider audience by making the analysis process visual. Comprehending the meaning buried in pages of statistical test results—p-values, standard deviations, error terms, degrees of freedom and on and on—is a mind-boggling task even for experts, but Sall knew that just about anyone could look at a well-drawn graph and understand things about his or her data.

JMP always leads every analysis with graphs, so that researchers needn't waste time poring over statistics when those graphs make it intuitively obvious whether they are on the right analysis path or not.

X86 Assembly/Control Flow

JMP also groups related analyses together and presents them in the order a researcher would need them in the course of a sound data exploration process. Researchers do not have to wrack their brains to remember which procedure might be helpful next.

Instead, JMP provides the tools that are appropriate at each stage. Further, all of JMP's graphs and data tables are dynamically linked, so that users can point and click to select points in a graph or bars in a histogram and instantly see where those points are represented in all other open graphs and data tables. Setting aside for a moment what it takes to understand statistics, consider what it takes to calculate statistics.

For a researcher to compute a standard deviation on thousands of observations using only a pencil and paper could take weeks or months. When he created SAS in the early s, Jim Goodnight's idea was to store all that data in a file and then write procedures that could be used and reused to compute statistics on any file.

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It's an idea that seems ludicrously simple today, but it was revolutionary at the time. The agricultural scientists using SAS could perform calculations over and over again on new data without having to pay for computer scientists to write and rewrite programs. Instead of taking weeks, these computations took hours.Jump to navigation. For years, PC programmers used x86 assembly to write performance-critical code. However, bit PCs are being replaced with bit ones, and the underlying assembly code has changed.

This white paper is an introduction to x64 assembly. No prior knowledge of x86 code is needed, although it makes the transition easier. We call this intersection flavor x This white paper won't cover hardware details such as caches, branch prediction, and other advanced topics.

Several references will be given at the end of the article for further reading in these areas. Assembly knowledge is useful for debugging code - sometimes a compiler makes incorrect assembly code and stepping through the code in a debugger helps locate the cause. Code optimizers sometimes make mistakes. Another use for assembly is interfacing with or fixing code for which you have no source code. Assembly is necessary if you want to know how your language of choice works under the hood - why some things are slow and others are fast.

Finally, assembly code knowledge is indispensable when diagnosing malware. When learning assembly for a given platform, the first place to start is to learn the register set.

General Architecture Since the bit registers allow access for many sizes and locations, we define a byte as 8 bits, a word as 16 bits, a double word as 32 bits, a quadword as 64 bits, and a double quadword as bits. Intel stores bytes "little endian," meaning lower significant bytes are stored in lower memory addresses. The second eight are named R8-R Note there is no R8H. The bit instruction pointer RIP points to the next instruction to be executed, and supports a bit flat memory model.

Memory address layout in current operating systems is covered later. The stack pointer RSP points to the last item pushed onto the stack, which grows toward lower addresses. This is formed from the x86 bit register EFLAGS by adding a higher 32 bits which are reserved and currently unused. Table 1 lists the most useful flags.

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Most of the other flags are used for operating system level tasks and should always be set to the value previously read. Table 1 - Common Flags.

FPR can each store one value of the types shown in Table 2. Floating point operations conform to IEEE These registers share space with the eight bit MMX registers. Table 2 - Floating Point Types. Binary Coded Decimal BCD is supported by a few 8-bit instructions, and an oddball format supported on the floating point registers gives an 80 bit, 17 digit BCD type.

x64 jmp

The sixteen bit XMM registers eight more than x86 are covered in more detail. The most notable performance opcode is RDTSC, which is used to count processor cycles for profiling small pieces of code.We got a few nice features from the new architecture of x64, like larger memory addressing, more registers so fast call is the standard up to three registers and the rest get on the stackand of course, a wider bandwidth of 64 bits, etc.

AMD had a once in a life opportunity to change the ISA instruction set architecture a bit and to make it much better, but instead, they only added a very few new instructions, canceled a lot, and left the decoding as hard as before.

Probably they were in a crazy rush, so that time Intel had to catch up with them! The problem we face when hooking a function is how many bytes we will need to override. I already talked about Hot Patching and branching in x But I have never talked at length about x Usually most hookers use the JMP relative instruction 0xE9which is possibly useful for x64 as well.

I also searched a bit over the inet to look for more info and found some interesting approaches. I decided to talk about them here and describe how they work. This one is almost optimal, you can branch everywhere in the address space, it takes only 12 bytes. It suffers a destruction of a register. Of course, by the ABI Application Binary Interface which the compiler implements, some registers are defined as volatile, means you can use them almost any time without worrying or needing to restore them.

Analyzing the function using a disassembler you may be able to know which register you can use safely. The first push, although pushes a 32 bits value, really allocates 64 bits value on the stack.

Then if the high half of the address is non zero, you will have to write it directly to the stack. So it takes 14 bytes as well. In the world of firewalls which do tons of hookingsfor instance, hooking this function twice with two different methods, will probably lead to a crash, since most hooking engines disassemble the instructions, you will get garbage beginning with the second instruction.

Because the addressing mode really supports 64 bit values.

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It takes 12 bytes. Needless to say, it dirties a register.

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Each method has its own pros and cons. It seems you can do best by choosing a specific method according to the difference from the hooked function to the target trampoline address. This entry was posted on Sunday, September 27th, at am and is filed under Assembly.

You can follow any responses to this entry through the RSS 2. You can leave a responseor trackback from your own site. Probably need store rax to memory. And why are you so worried about the number of writable memory? Thanks serge. This is 12 bytes indeed!

Is an extremly BAD idea, because it is guaranteed to generate a mispredicted branch. All x86 processors have a Call-RET table. Intel already tried a fresh start with Itanium IA It totally faceplanted. I mean, talk about crash and burn. AMD64 is incremental move, and even then it was an extremely risky business proposition. AMD bosses either had nuts of steel or something forced their hand. Instead, it looks in the memory at address RAX and from there, it reads the destination address to jump to.

I just cannot find such instruction after disassembling a bunch of binaries.Transfers program control to a different point in the instruction stream without recording return information. The destination target operand specifies the address of the instruction being jumped to. This operand can be an immediate value, a general-purpose register, or a memory location.

x64 jmp

This instruction can be used to execute four different types of jumps: - Near jump-A jump to an instruction within the current code segment the segment currently pointed to by the CS registersometimes referred to as an intrasegment jump. Near and Short Jumps. When executing a near jump, the processor jumps to the address within the current code segment that is specified with the target operand. The target operand specifies either an absolute offset that is an offset from the base of the code segment or a relative offset a signed displacement relative to the current value of the instruction pointer in the EIP register.

A near jump to a relative offset of 8-bits rel8 is referred to as a short jump. The CS register is not changed on near and short jumps. The operand-size attribute determines the size of the target operand 16 or 32 bits.

Absolute offsets are loaded directly into the EIP register. If the operand-size attribute is 16, the upper two bytes of the EIP register are cleared, resulting in a maximum instruction pointer size of 16 bits. A relative offset rel8, rel16, or rel32 is generally specified as a label in assembly code, but at the machine code level, it is encoded as a signed 8-,or bit immediate value.

This value is added to the value in the EIP register. When using relative offsets, the opcode for short vs. When executing a far jump in realaddress or virtual mode, the processor jumps to the code segment and offset specified with the target operand.

Here the target operand specifies an absolute far address either directly with a pointer ptr or ptr or indirectly with a memory location m or m With the pointer method, the segment and address of the called procedure is encoded in the instruction, using a 4-byte bit operand size or 6-byte bit operand size far address immediate.

With the indirect method, the target operand specifies a memory location that contains a 4-byte bit operand size or 6-byte bit operand size far address. If the operand-size attribute is 16, the upper two bytes of the EIP register are cleared.

Far Jumps in Protected Mode. When the processor is operating in protected mode, the JMP instruction can be used to perform the following three types of far jumps:. The JMP instruction cannot be used to perform inter-privilege-level far jumps.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service. The dark mode beta is finally here.

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Change your preferences any time. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. Have a doubt regarding the hex code conversion of JMP machine instruction. I have the absolute address I want to jump to, say "JMP 0x". First of all, is this allowed?

If yes, what would be the corresponding hex code? I am working on x86 64b architecture. I have tried to print out the hex code from the diassem output in gdb, but there is no consistency, ie, I do not see the destination address in the hex code. There is no jump of the form JMP absaddr to an absolute address in 64 bit mode. The operand of a jump is always a 32 bit relative displacement to ripwhich gets sign extended to 64 bit.

The reason you see no consistency is possibly that the offset depends on the the current instruction pointer and you didn't recognize that. How did I know these hex codes? Well, I did ask my compiler. I compiled with gcc -c and disassembled with objdump.

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I didn't bother to use Intel syntax, because I don't need it. If you don't want to use a register for whatever reason, it's also possible to encode a 64 bit absolute immediate jump as.

Learn more. Asked 8 years ago. Active 1 year, 4 months ago. Viewed 27k times. I am new to hex code and machine instructions, so pardon my ignorance. Deepanjan Mazumdar Deepanjan Mazumdar 1, 2 2 gold badges 11 11 silver badges 19 19 bronze badges. If the jump target is in range, some toolchains e. Active Oldest Votes. Gunther Piez Gunther Piez Thank you for the answer.

This really helped me. I have marked your post as "useful". Can you please tell where I can find description of this syntax?

JMP — Jump

If you don't want to use a register for whatever reason, it's also possible to encode a 64 bit absolute immediate jump as ff 25 00 00 00 00 jmp qword ptr [rip] yo ur ad dr re ss he re some random assembly rip refers to the instruction pointer AFTER the jmp instruction itself, so it's a pointer to your address.

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