I have the following piece of code that I have to debug:
JavaScript
x
global _start_start:pop espjs 0x36xor [eax+edi*2+0x43],ebxxor [eax+edi*2+0x35],blxor [eax+edi*2+0x36],blcmp [eax+edi*2+0x37],blss pop espjs 0x49aaapop espjs 0x52xor al,0x5cjs 0x56xor al,0x5cjs 0x59cmp [eax+edi*2+0x37],blxor ebx,[eax+edi*2+0x32]xor al,0x5cjs 0x61xor eax,0x3532785cpop espjs 0x6dcmp [eax+edi*2+0x32],blxor [eax+edi*2+0x32],blxor ebx,[eax+edi*2+0x32]xor eax,0x3332785cpop espjs 0x81cmp [eax+edi*2+0x37],blcmp [eax+edi*2+0x32],blxor al,0x5cjs 0x8exor eax,0x3532785cpop espjs 0x95cmp [eax+edi*2+0x37],blcmp [eax+edi*2+0x32],blxor [eax+edi*2+0x37],blxor bl,[eax+edi*2+0x32]xor [eax+edi*2+0x36],blcmp [eax+edi*2+0x37],blxor [eax+edi*2+0x37],blxor [eax+edi*2+0x37],blxor eax,0x3637785cpop espjs 0xbdcmp [eax+edi*2+0x32],blaaapop espjs 0xc6xor al,0x5cjs 0xcacmp [eax+edi*2+0x32],blaaapop espjs 0xd1cmp [eax+edi*2+0x37],blcmp [eax+edi*2+0x32],ebxaaapop espjs 0xd9xor al,0x5cjs 0xe2xor bl,[eax+edi*2+0x36]cmp [eax+edi*2+0x37],blxor bl,[eax+edi*2+0x37]cmp [eax+edi*2+0x37],blcmp [eax+edi*2+0x37],ebxcmp [eax+edi*2+0x36],blcmp [eax+edi*2+0x37],blss pop espjs 0xfdaaapop espjs 0x106xor [eax+edi*2+0x32],blxor eax,0x3836785cpop espjs 0x112cmp [eax+edi*2+0x37],blxor ebx,[eax+edi*2+0x32]xor ebx,[eax+edi*2+0x32]aaapop espjs 0x121cmp [eax+edi*2+0x32],blxor [eax+edi*2+0x37],blcmp [eax+edi*2+0x32],ebxxor bl,[eax+edi*2+0x37]xor eax,0x3836785cpop espjs 0x13axor [eax+edi*2+0x37],blxor [eax+edi*2+0x32],ebxxor al,0x5cjs 0x141xor ebx,[eax+edi*2+0x36]cmp [eax+edi*2+0x37],blxor [eax+edi*2+0x37],ebxxor ebx,[eax+edi*2+0x37]cmp [eax+edi*2+0x37],ebxxor [eax+edi*2+0x36],blcmp [eax+edi*2+0x32],blxor eax,0x3937785cpop espjs 0x16axor bl,[eax+edi*2+0x37]xor bl,[eax+edi*2+0x36]cmp [eax+edi*2+0x32],blaaapop espjs 0x17acmp [eax+edi*2+0x32],blaaapop espjs 0x182xor eax,0x3836785cpop espjs 0x18acmp [eax+edi*2+0x37],blxor [eax+edi*2+0x37],blxor ebx,[eax+edi*2+0x37]xor eax,0x3836785cpop espjs 0x19exor bl,[eax+edi*2+0x37]cmp [eax+edi*2+0x32],blxor ebx,[eax+edi*2+0x37]xor eax,0x3836785cpop espjs 0x1adxor eax,0x3032785cpop espjs 0x1baxor [eax+edi*2+0x32],blxor al,0x5cjs 0x1c1cmp [eax+edi*2+0x37],blxor bl,[eax+edi*2+0x32]xor eax,0x3637785cpop espjs 0x1d2xor ebx,[eax+edi*2+0x36]cmp [eax+edi*2+0x37],blxor bl,[eax+edi*2+0x32]xor [eax+edi*2+0x37],blxor ebx,[eax+edi*2+0x37]xor bl,[eax+edi*2+0x36]cmp [eax+edi*2+0x37],blxor [eax+edi*2+0x32],ebxxor [eax+edi*2+0x37],blxor [eax+edi*2+0x32],ebxxor bl,[eax+edi*2+0x36]cmp [eax+edi*2+0x32],blxor ebx,[eax+edi*2+0x37]xor eax,0x3037785cpop espjs 0x20exor bl,[eax+edi*2+0x36]cmp [eax+edi*2+0x32],blxor bl,[eax+edi*2+0x37]xor al,0x5cjs 0x219xor eax,0x3837785cpop espjs 0x225cmp [eax+edi*2+0x37],blxor [eax+edi*2+0x37],ebxaaapop espjs 0x232xor eax,0x3137785cpop espjs 0x239cmp [eax+edi*2+0x32],blaaapop espjs 0x242xor bl,[eax+edi*2+0x37]aaapop espjs 0x245xor bl,[eax+edi*2+0x36]cmp [eax+edi*2+0x37],blxor [eax+edi*2+0x37],blxor [eax+edi*2+0x32],blaaapop espjs 0x259xor eax,0x3836785cpop espjs 0x266aaapop espjs 0x26axor ebx,[eax+edi*2+0x37]cmp [eax+edi*2+0x32],blxor al,0x5cjs 0x275cmp [eax+edi*2+0x37],blxor bl,[eax+edi*2+0x37]cmp [eax+edi*2+0x37],blaaapop espjs 0x286xor al,0x5cjs 0x289cmp [eax+edi*2+0x32],blaaapop espjs 0x292aaapop espjs 0x291aaapop espjs 0x295xor bl,[eax+edi*2+0x36]cmp [eax+edi*2+0x32],blxor bl,[eax+edi*2+0x37]xor al,0x5cjs 0x2a5xor bl,[eax+edi*2+0x37]xor eax,0x3836785cpop espjs 0x2b6xor ebx,[eax+edi*2+0x37]aaapop espjs 0x2bexor [eax+edi*2+0x37],blxor [eax+edi*2+0x35],blxor al,0x5cjs 0x2c8inc ebppop espjs 0x2cfinc edxpop espjs 0x2e1inc ebppop espjs 0x2d7inc edxpop espjs 0x2e7aaapop espjs 0x2edinc ebxpop espjs 0x2edcmp [eax+edi*2+0x38],ebxxor [eax+edi*2+0x30],blxor [eax+edi*2+0x30],blxor [eax+edi*2+0x30],blxor [eax+edi*2+0x42],blinc edxpop espjs 0x2f7xor [eax+edi*2+0x30],ebxxor [eax+edi*2+0x30],blxor [eax+edi*2+0x30],blxor [eax+edi*2+0x33],blxor [eax+edi*2+0x43],ebxxor [eax+edi*2+0x35],blxor [eax+edi*2+0x41],blinc ebxpop espjs 0x316xor ebx,[eax+edi*2+0x43]xor ebx,[eax+edi*2+0x41]inc ecxpop espjs 0x334xor bl,[eax+edi*2+0x46]inc ecxpop espjs 0x32cxor al,0x5cjs 0x330inc ebppop espjs 0x342inc ebxdb 0x0aAfter compiling and running that code I obtain a segmentation fault error, it seems that something goes wrong after the 5th line. My linux asm knowledge is very basic, any hints or ideas about what is exactly going wrong and how to fix it?
This piece of code is a part of a debugging exercise, I’m doing that for auto-learning only, this is not a part of any homework or something.
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Answer
I have compiled your example and then looked at it using hexdump:
(I had to add BITS 32 to it to compile in 32-bit mode, because I’m using Linux-64):
JavaScript
$ vi test.asm$ nasm test.asm$ hexdump -C test00000000 5c 0f 88 2f 00 00 00 31 5c 78 43 30 5c 78 35 30 |../1xC0x50|00000010 5c 78 36 38 5c 78 37 36 5c 0f 88 2a 00 00 00 37 |x68x76..*7|00000020 5c 0f 88 2b 00 00 00 34 5c 0f 88 27 00 00 00 34 |..+4..'...4|00000030 5c 0f 88 22 00 00 00 38 5c 78 37 33 5c 78 32 34 |.."...8x73x24|00000040 5c 0f 88 1a 00 00 00 35 5c 78 32 35 5c 0f 88 1a |5x25|00000050 00 00 00 38 5c 78 32 30 5c 78 32 33 5c 78 32 35 |8x20x23x25|00000060 5c 78 32 33 5c 0f 88 16 00 00 00 38 5c 78 37 38 |x238x78|00000070 5c 78 32 34 5c 0f 88 13 00 00 00 35 5c 78 32 35 |x245x25|00000080 5c 0f 88 0e 00 00 00 38 5c 78 37 38 5c 78 32 30 |8x78x20|..Do you see the pattern? At the right column (ASCII mode) you can see a lot of literal xNN, that is not the byte NN but the characters '' 'x' and two numbers!
My guess is that you are debugging a dump of some binary code, but that code has not been properly dumped. Thus the assembly you are looking at is nonsense.