How to use a logical address with an FS or GS base in gdb?
gdb, memory-segmentation, x86
Solution
how can i read the memory at "%gs:0x14" in gdb
You can't: there is no way for GDB to know how the segment to which `%gs` refers to has been set up.
or translate this logical address to a linear address that i could use in x command
Again, you can't do this in general. However, you appear to be on 32-bit x86 Linux, and there you can do that -- the `%gs` is set up to point to the thread descriptor via `set_thread_area` system call.
You can do `catch syscall set_thread_area` in GDB, and examine the parameters (each thread will have one such call). The code to actually do that is here. Once you know how `%gs` has been set up, just add 0x14 to the `base_addr`, and you are done.
Problem
gdb provides functionality to read or write to a specific linear address, for example: ``` (gdb) x/1wx 0x080483e4 0x80483e4 <main>: 0x83e58955 (gdb) ``` but how do you specify a logical address ? I came accross the following instruction: ``` 0x0804841a <+6>: mov %gs:0x14,%eax ``` how can i read the memory at "%gs:0x14" in gdb, or translate this logical address to a linear address that i could use in `x` command ? note: i know that i could simply read %eax after this instruction, but that is not my concern