CODEWITHSUNDEEP
debuggingassemblygdbx86-64disassembly
Karan Tejas
Karan Tejas

Reputation: 59

Why is there a "±" in lea rax, [ rip ± 0xeb3]?

I just started learning about assembly language in Kali Linux in VMware. I have a Ryzen 5 CPU. In the below code snippet, I have a few things I don't understand.

(gdb) list
1       #include<stdio.h>
2
3       int main(){
4               int i;
5               for(i = 0 ; i < 10 ; i++){
6                       printf("Hello World!\n");
7               }
8               return 0;
9       }
(gdb) disassemble main
Dump of assembler code for function main:
   0x0000000000001139 <+0>:     push   rbp
   0x000000000000113a <+1>:     mov    rbp,rsp
   0x000000000000113d <+4>:     sub    rsp,0x10
   0x0000000000001141 <+8>:     mov    DWORD PTR [rbp-0x4],0x0
   0x0000000000001148 <+15>:    jmp    0x115d <main+36>
   0x000000000000114a <+17>:    lea    rax,[rip±0xeb3]        # 0x2004
   0x0000000000001151 <+24>:    mov    rdi,rax
   0x0000000000001154 <+27>:    call   0x1030 <puts@plt>
   0x0000000000001159 <+32>:    add    DWORD PTR [rbp-0x4],0x1
   0x000000000000115d <+36>:    cmp    DWORD PTR [rbp-0x4],0x9
   0x0000000000001161 <+40>:    jle    0x114a <main+17>
   0x0000000000001163 <+42>:    mov    eax,0x0
   0x0000000000001168 <+47>:    leave  
   0x0000000000001169 <+48>:    ret    
End of assembler dump.
(gdb)

Edit:

gdb -v        
GNU gdb (Debian 12.1-3) 12.1
Copyright (C) 2022 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

Upvotes: 5

Views: 440

Answers (1)

Margaret Bloom
Margaret Bloom

Reputation: 44066

It's not a plus-minus (±, Unicode point 0x00b1), it's an underlined plus.
If you copy-paste it, you get only a plus (+).

GDB 12.1 uses Python to colorize each line of its disassembler output. Specifically, it uses the Pygments packages, which, at the current version 2.11.2, handle x64 code badly, here's a test case:

from pygments import formatters, lexers, highlight
 
def colorize_disasm(content, gdbarch):
    # Don't want any errors.
    try:
        lexer = lexers.get_lexer_by_name("asm")
        formatter = formatters.TerminalFormatter()
        return highlight(content, lexer, formatter).rstrip().encode()
    except:
        return None
 
 
print(colorize_disasm("lea [rip+0x211]  #test", None).decode())

Wrong Pygments output for RIP-relative operands

The (yet to be released) next version uses an entirely different coloring code, where each disassembler function can introduce style markers in its output and the disassemble command (see gdb/disassemble.c) translates those markers into terminal escapes.

Upvotes: 4

Related Questions