What does jmpq do

Riyazul Aboobucker. So when the assembler sees mov eax, msg it knows that msg is a label corresponding to an address in the data segment, so it generates an instruction to load that address into eax.

When it sees mov eax, [msg] it generates an instruction to load bits the size of register eax from memory at address of msg. But it looks like it treats it as an alias for [] Now LEA is a funny instruction -- it has basically the same format as a move from memory, but instead of reading memory, it stores the address it would have read from into the destination register. So lea eax, msg makes no sense -- the source is the label address msg , which is a link time constant and is not in memory anywhere.

So when you say gdb p msg it looks at msg and says "that looks like a variable, so lets get the current value of that variable and print that". Dave B. Only authorized users can answer the question. Please sign in first, or register a free account. Not the answer you're looking for? Browse other questions tagged : assembly.

When executing a far jump through a call gate, the segment selector specified by the target operand identifies the call gate. The offset part of the target operand is ignored. The processor then jumps to the code segment specified in the call gate descriptor and begins executing the instruction at the offset specified in the call gate. No stack switch occurs. Here again, the target operand can specify the far address of the call gate either directly with a pointer ptr or ptr or indirectly with a memory location m or m Executing a task switch with the JMP instruction is somewhat similar to executing a jump through a call gate.

Here the target operand specifies the segment selector of the task gate for the task being switched to and the offset part of the target operand is ignored. This instruction pointer value is loaded into the EIP register so that the task begins executing again at this next instruction.

The JMP instruction can also specify the segment selector of the TSS directly, which eliminates the indirection of the task gate. A return to the previous task can thus not be carried out by executing the IRET instruction. In Bit Mode. If a selector points to a gate, then RIP equals the bit displacement taken from gate; else RIP equals the zero-extended offset from the far pointer referenced in the instruction.

Instruction ordering. Instructions following a far jump may be fetched from memory before earlier instructions complete execution, but they will not execute even speculatively until all instructions prior to the far jump have completed execution the later instructions may execute before data stored by the earlier instructions have become globally visible.

Certain situations may lead to the next sequential instruction after a near indirect JMP being speculatively executed. This section sheds some light on what actually happens with the Java application code when going through the JVM.

The code. In this video we introduce the lab throughout the course. We formulate the problem provide the codebase structure and train a simple Multilayer Perceptron on. Instruction ordering. Instructions following a far jump may be fetched from memory before earlier instructions complete execution but they will not execute. Conditional Instructions. Unconditional jump. This is performed by the JMP instruction. Conditional execution often involves a transfer of control to the. Callee saved.

These registers are. The x86 instruction set refers to the set of instructions that x86compatible microprocessors support. The instructions are usually part of an executable. The assembler in Intel mode will automatically select the correct jmp encoding for you. From a different manufacturer, using a different paradigm.

Note that Intel does not specify different syntaxes for the relative and absolute forms of the jmp. The beauty of this is that the assembler automatically uses the proper jump for you. To make gnu use Intel syntax, this will put things back the way they are designed by Intel and away from the PDP7 syntax used by gnu.

An l operand-size suffix implies an indirect jmp , unlike with calll main which is still a relative near-call. And since you're using it with an operand like main , it becomes a memory-indirect jump, doing a data load from main and using that as the new EIP value. Using jmpl is optional in all of these.