Contents
What is GS in assembly?
GS is a segment register, its use in linux can be read up on here (its basically used for per thread data). mov %gs:0x14,êx xor %gs:0x14,êx. this code is used to validate that the stack hasn’t exploded or been corrupted, using a canary value stored at GS+0x14, see this.
What are segment registers?
The segment registers stores the starting addresses of a segment. To get the exact location of data or instruction within a segment, an offset value (or displacement) is required.
What does FS and GS stand for?
The registers FS and GS are segment registers. They have no processor-defined purpose, but instead are given purpose by the OS’s running them. In Windows 64-bit the GS register is used to point to operating system defined structures. FS and GS are commonly used by OS kernels to access thread-specific memory.
How does CDQ work?
The CDQ instruction copies the sign (bit 31) of the value in the EAX register into every bit position in the EDX register. The CQO instruction can be used to produce a double quadword dividend from a quadword before a quadword division.
What is the purpose of the GS and FS registers?
In Windows 64-bit the GS register is used to point to operating system defined structures. FS and GS are commonly used by OS kernels to access thread-specific memory. In windows, the GS register is used to manage thread-specific memory.
What are the extra registers in assembly programming?
Apart from the DS, CS and SS registers, there are other extra segment registers – ES (extra segment), FS and GS, which provide additional segments for storing data. In assembly programming, a program needs to access the memory locations. All memory locations within a segment are relative to the starting address of the segment.
What is the ” ES ” Register intended for?
ES is used to access everything else (*2), everything beyond the 64 KiB of DS. Like the text of a word processor, the cells of a spread sheet, or the picture data of a graphics program and so on. Unlike often assumed, this data doesn’t get as much accessed, so needing a prefix hurts less than using longer address fields.
What do you need to know about assembly registers?
Segment Registers 1 Code Segment − It contains all the instructions to be executed. A 16-bit Code Segment register or CS register stores the starting address of the code segment. 2 Data Segment − It contains data, constants and work areas. 3 Stack Segment − It contains data and return addresses of procedures or subroutines.