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libxml2 personal notes
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root@research:~/dev# cat main.c | |
#include <stdio.h> | |
#include <libxml/parser.h> | |
int main(int argc, char *argv[]) | |
{ | |
xmlDocPtr doc; | |
xmlNodePtr node; | |
/* read xmlfile */ | |
doc = xmlReadFile(argv[1], 0, 0); | |
if (!argv[1]) | |
{ | |
printf("[!] You input an null data: '%s'\n", argv[1]); | |
return -1; | |
} | |
node = xmlDocGetRootElement(doc); | |
if (!node) | |
{ | |
puts("[!] Make sure that is a correct file.\n"); | |
return -1; | |
} | |
return 0; | |
} | |
-------------------------- %< -------------------------- | |
0400691 <+1>: mov 0x8(%rsi),%rdi ;align stack for the 3rd parameter, making argv[1] | |
;pointer points to '*filename' | |
0400695 <+5>: mov %rsi,%rbx ;copies data from parameter to argument | |
0400698 <+8>: xor %edx,%edx ;initiates the register with value zero | |
040069a <+10>: xor %esi,%esi ;initiates the register with value zero | |
callq 0x400640 <xmlReadFile@plt> ;exec function: xmlReadFile(argv[1], 0, 0) | |
4006a1 <+17>: cmpq $0x0,0x8(%rbx) ;knowing that $0x0 corresponds to 'null terminator' | |
; that is equals to 'NULL', then it is a check | |
;if "*argv[]" points to NULL data. | |
4006a6 <+22>: je 0x4006b9 <main+41> ;jump to "ret" (0x4006b9) whether is NULL | |
;is it looks like: if (!argv[1]) { return -1; } | |
4006a8 <+24>: mov %rax,%rdi ;copies the data stored in rdi (*filename) to rax | |
4006ab <+27>: callq 0x400650 <xmlDocGetRootElement@plt> ;exec function "xmlDocGetRootElement(rax);" | |
4006b0 <+32>: test %rax,%rax ;set rax to '1'(true) if rax is '0'(false), then exec next current instruction | |
4006b3 <+35>: je 0x4006cc <main+60> ; if rax was set to "1" jump to address 0x4006cc | |
; reading the libxml2 documentation, note that the function "xmlDocGetRootElement" | |
; has 2 behaviors defined --- from xmlsoft: "Returns: the #xmlNodePtr for the root or NULL" | |
; exec this 3 instructions below if rax was set to '0' -- xmlDocGetRootElement's behavior | |
4006b5 <+37>: xor %eax,%eax ; set eax to 0 | |
4006b7 <+39>: pop %rbx ; remove rbx from stack | |
4006b8 <+40>: retq ; return eax | |
4006b9 <+41>: xor %esi,%esi ;reset the 32-bit LSB of the RSI register, - WORD size. | |
4006bb <+43>: mov $0x400868,%edi ;input the value stored in "0x40086" into EDI register. | |
4006c0 <+48>: xor %eax,%eax ;set EAX to '0' | |
4006c2 <+50>: callq 0x400630 <printf@plt> ;callq belongs to SIMD (single instruction, multiple data) | |
;perform the printf() execution and pushes the current address | |
;of instruction pointer (%rip) onto the stack and jumps to it. | |
; return after callq | |
04006c7 <+55>: or $0xffffffff,%eax ;set to '1' all bits (32-bits length) | |
04006ca <+58>: pop %rbx ;remove rbx from the stack | |
04006cb <+59>: retq ;return "-1" (0xffffffff) | |
; calling "puts" function with message stored at "$0x400890" and do the same thing as above and return -1 | |
04006cc <+60>: mov $0x400890,%edi | |
04006d1 <+65>: callq 0x400660 <puts@plt> | |
04006d6 <+70>: or $0xffffffff,%eax | |
04006d9 <+73>: pop %rbx | |
04006da <+74>: retq | |
-------------------------- %< -------------------------- |
[Warning] This note has no intention of teaching. They're just random notes and outburst during my studies two years later.
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Dropping this as public 2 years later.