# ELF Msingi wa Taarifa {{#include ../../banners/hacktricks-training.md}} ## Vichwa vya Programu Vinavyoelezea kwa loader jinsi ya kupakia **ELF** kwenye kumbukumbu: ```bash readelf -lW lnstat Elf file type is DYN (Position-Independent Executable file) Entry point 0x1c00 There are 9 program headers, starting at offset 64 Program Headers: Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align PHDR 0x000040 0x0000000000000040 0x0000000000000040 0x0001f8 0x0001f8 R 0x8 INTERP 0x000238 0x0000000000000238 0x0000000000000238 0x00001b 0x00001b R 0x1 [Requesting program interpreter: /lib/ld-linux-aarch64.so.1] LOAD 0x000000 0x0000000000000000 0x0000000000000000 0x003f7c 0x003f7c R E 0x10000 LOAD 0x00fc48 0x000000000001fc48 0x000000000001fc48 0x000528 0x001190 RW 0x10000 DYNAMIC 0x00fc58 0x000000000001fc58 0x000000000001fc58 0x000200 0x000200 RW 0x8 NOTE 0x000254 0x0000000000000254 0x0000000000000254 0x0000e0 0x0000e0 R 0x4 GNU_EH_FRAME 0x003610 0x0000000000003610 0x0000000000003610 0x0001b4 0x0001b4 R 0x4 GNU_STACK 0x000000 0x0000000000000000 0x0000000000000000 0x000000 0x000000 RW 0x10 GNU_RELRO 0x00fc48 0x000000000001fc48 0x000000000001fc48 0x0003b8 0x0003b8 R 0x1 Section to Segment mapping: Segment Sections... 00 01 .interp 02 .interp .note.gnu.build-id .note.ABI-tag .note.package .gnu.hash .dynsym .dynstr .gnu.version .gnu.version_r .rela.dyn .rela.plt .init .plt .text .fini .rodata .eh_frame_hdr .eh_frame 03 .init_array .fini_array .dynamic .got .data .bss 04 .dynamic 05 .note.gnu.build-id .note.ABI-tag .note.package 06 .eh_frame_hdr 07 08 .init_array .fini_array .dynamic .got ``` Programu ya awali ina **vichwa vya programu 9**, kisha, **ramani ya sehemu** inaonyesha katika kichwa gani cha programu (kuanzia 00 hadi 08) **kila sehemu iko**. ### PHDR - Kichwa cha Programu Inajumuisha meza za vichwa vya programu na metadata yenyewe. ### INTERP Inaonyesha njia ya loader inayotumika kupakia binary kwenye kumbukumbu. ### LOAD Vichwa hivi vinatumika kuonyesha **jinsi ya kupakia binary kwenye kumbukumbu.**\ Kila kichwa cha **LOAD** kinaonyesha eneo la **kumbukumbu** (ukubwa, ruhusa na usawa) na inaonyesha bytes za ELF **binary za kunakili huko**. Kwa mfano, ya pili ina ukubwa wa 0x1190, inapaswa kuwa katika 0x1fc48 ikiwa na ruhusa za kusoma na kuandika na itajazwa na 0x528 kutoka kwa ofset 0xfc48 (haijaza nafasi yote iliyohifadhiwa). Kumbukumbu hii itakuwa na sehemu `.init_array .fini_array .dynamic .got .data .bss`. ### DYNAMIC Kichwa hiki husaidia kuunganisha programu na utegemezi wa maktaba zao na kutekeleza uhamasishaji. Angalia sehemu **`.dynamic`**. ### NOTE Hii inahifadhi taarifa za metadata za muuzaji kuhusu binary. ### GNU_EH_FRAME Inafafanua eneo la meza za kuondoa stack, zinazotumiwa na debuggers na kazi za usimamizi wa makosa za C++. ### GNU_STACK Inajumuisha usanidi wa ulinzi wa kuzuia utekelezaji wa stack. Ikiwa imewezeshwa, binary haitakuwa na uwezo wa kutekeleza msimbo kutoka kwenye stack. ### GNU_RELRO Inaonyesha usanidi wa RELRO (Relocation Read-Only) wa binary. Ulinzi huu utaashiria kama isiyo na kuandika sehemu fulani za kumbukumbu (kama `GOT` au meza za `init` na `fini`) baada ya programu kupakiwa na kabla ya kuanza kutekelezwa. Katika mfano wa awali inakopi bytes 0x3b8 hadi 0x1fc48 kama zisizo na kuandika zikihusisha sehemu `.init_array .fini_array .dynamic .got .data .bss`. Kumbuka kwamba RELRO inaweza kuwa ya sehemu au kamili, toleo la sehemu halilindi sehemu **`.plt.got`**, ambayo inatumika kwa **lazy binding** na inahitaji nafasi hii ya kumbukumbu kuwa na **ruhusa za kuandika** ili kuandika anwani za maktaba wakati wa kwanza mahali pake inatafutwa. ### TLS Inafafanua meza ya entries za TLS, ambayo inahifadhi taarifa kuhusu mabadiliko ya ndani ya thread. ## Vichwa vya Sehemu Vichwa vya sehemu vinatoa mtazamo wa kina zaidi wa binary ya ELF. ``` objdump lnstat -h lnstat: file format elf64-littleaarch64 Sections: Idx Name Size VMA LMA File off Algn 0 .interp 0000001b 0000000000000238 0000000000000238 00000238 2**0 CONTENTS, ALLOC, LOAD, READONLY, DATA 1 .note.gnu.build-id 00000024 0000000000000254 0000000000000254 00000254 2**2 CONTENTS, ALLOC, LOAD, READONLY, DATA 2 .note.ABI-tag 00000020 0000000000000278 0000000000000278 00000278 2**2 CONTENTS, ALLOC, LOAD, READONLY, DATA 3 .note.package 0000009c 0000000000000298 0000000000000298 00000298 2**2 CONTENTS, ALLOC, LOAD, READONLY, DATA 4 .gnu.hash 0000001c 0000000000000338 0000000000000338 00000338 2**3 CONTENTS, ALLOC, LOAD, READONLY, DATA 5 .dynsym 00000498 0000000000000358 0000000000000358 00000358 2**3 CONTENTS, ALLOC, LOAD, READONLY, DATA 6 .dynstr 000001fe 00000000000007f0 00000000000007f0 000007f0 2**0 CONTENTS, ALLOC, LOAD, READONLY, DATA 7 .gnu.version 00000062 00000000000009ee 00000000000009ee 000009ee 2**1 CONTENTS, ALLOC, LOAD, READONLY, DATA 8 .gnu.version_r 00000050 0000000000000a50 0000000000000a50 00000a50 2**3 CONTENTS, ALLOC, LOAD, READONLY, DATA 9 .rela.dyn 00000228 0000000000000aa0 0000000000000aa0 00000aa0 2**3 CONTENTS, ALLOC, LOAD, READONLY, DATA 10 .rela.plt 000003c0 0000000000000cc8 0000000000000cc8 00000cc8 2**3 CONTENTS, ALLOC, LOAD, READONLY, DATA 11 .init 00000018 0000000000001088 0000000000001088 00001088 2**2 CONTENTS, ALLOC, LOAD, READONLY, CODE 12 .plt 000002a0 00000000000010a0 00000000000010a0 000010a0 2**4 CONTENTS, ALLOC, LOAD, READONLY, CODE 13 .text 00001c34 0000000000001340 0000000000001340 00001340 2**6 CONTENTS, ALLOC, LOAD, READONLY, CODE 14 .fini 00000014 0000000000002f74 0000000000002f74 00002f74 2**2 CONTENTS, ALLOC, LOAD, READONLY, CODE 15 .rodata 00000686 0000000000002f88 0000000000002f88 00002f88 2**3 CONTENTS, ALLOC, LOAD, READONLY, DATA 16 .eh_frame_hdr 000001b4 0000000000003610 0000000000003610 00003610 2**2 CONTENTS, ALLOC, LOAD, READONLY, DATA 17 .eh_frame 000007b4 00000000000037c8 00000000000037c8 000037c8 2**3 CONTENTS, ALLOC, LOAD, READONLY, DATA 18 .init_array 00000008 000000000001fc48 000000000001fc48 0000fc48 2**3 CONTENTS, ALLOC, LOAD, DATA 19 .fini_array 00000008 000000000001fc50 000000000001fc50 0000fc50 2**3 CONTENTS, ALLOC, LOAD, DATA 20 .dynamic 00000200 000000000001fc58 000000000001fc58 0000fc58 2**3 CONTENTS, ALLOC, LOAD, DATA 21 .got 000001a8 000000000001fe58 000000000001fe58 0000fe58 2**3 CONTENTS, ALLOC, LOAD, DATA 22 .data 00000170 0000000000020000 0000000000020000 00010000 2**3 CONTENTS, ALLOC, LOAD, DATA 23 .bss 00000c68 0000000000020170 0000000000020170 00010170 2**3 ALLOC 24 .gnu_debugaltlink 00000049 0000000000000000 0000000000000000 00010170 2**0 CONTENTS, READONLY 25 .gnu_debuglink 00000034 0000000000000000 0000000000000000 000101bc 2**2 CONTENTS, READONLY ``` Inayoonyesha pia mahali, ofseti, ruhusa lakini pia **aina ya data** ambayo sehemu hiyo ina. ### Sehemu za Meta - **String table**: Inayo kila nyuzi inayohitajika na faili la ELF (lakini si zile zinazotumiwa na programu). Kwa mfano, ina majina ya sehemu kama `.text` au `.data`. Na ikiwa `.text` iko kwenye ofseti 45 katika jedwali la nyuzi itatumia nambari **45** katika uwanja wa **jina**. - Ili kupata mahali ambapo jedwali la nyuzi liko, ELF ina kiashiria kwa jedwali la nyuzi. - **Symbol table**: Inayo taarifa kuhusu alama kama jina (ofseti katika jedwali la nyuzi), anwani, ukubwa na metadata zaidi kuhusu alama hiyo. ### Sehemu Kuu - **`.text`**: Maagizo ya programu ya kukimbia. - **`.data`**: Vigezo vya kimataifa vyenye thamani iliyofafanuliwa katika programu. - **`.bss`**: Vigezo vya kimataifa vilivyotelekezwa (au kuanzishwa kuwa sifuri). Vigezo hapa vinakaguliwa kiotomatiki kuwa sifuri hivyo kuzuia sifuri zisizohitajika kuongezwa kwenye binary. - **`.rodata`**: Vigezo vya kimataifa visivyobadilika (sehemu ya kusoma tu). - **`.tdata`** na **`.tbss`**: Kama .data na .bss wakati vigezo vya ndani ya thread vinapotumika (`__thread_local` katika C++ au `__thread` katika C). - **`.dynamic`**: Angalia hapa chini. ## Alama Alama ni mahali lenye jina katika programu ambalo linaweza kuwa kazi, kitu cha data cha kimataifa, vigezo vya ndani ya thread... ``` readelf -s lnstat Symbol table '.dynsym' contains 49 entries: Num: Value Size Type Bind Vis Ndx Name 0: 0000000000000000 0 NOTYPE LOCAL DEFAULT UND 1: 0000000000001088 0 SECTION LOCAL DEFAULT 12 .init 2: 0000000000020000 0 SECTION LOCAL DEFAULT 23 .data 3: 0000000000000000 0 FUNC GLOBAL DEFAULT UND strtok@GLIBC_2.17 (2) 4: 0000000000000000 0 FUNC GLOBAL DEFAULT UND s[...]@GLIBC_2.17 (2) 5: 0000000000000000 0 FUNC GLOBAL DEFAULT UND strlen@GLIBC_2.17 (2) 6: 0000000000000000 0 FUNC GLOBAL DEFAULT UND fputs@GLIBC_2.17 (2) 7: 0000000000000000 0 FUNC GLOBAL DEFAULT UND exit@GLIBC_2.17 (2) 8: 0000000000000000 0 FUNC GLOBAL DEFAULT UND _[...]@GLIBC_2.34 (3) 9: 0000000000000000 0 FUNC GLOBAL DEFAULT UND perror@GLIBC_2.17 (2) 10: 0000000000000000 0 NOTYPE WEAK DEFAULT UND _ITM_deregisterT[...] 11: 0000000000000000 0 FUNC WEAK DEFAULT UND _[...]@GLIBC_2.17 (2) 12: 0000000000000000 0 FUNC GLOBAL DEFAULT UND putc@GLIBC_2.17 (2) [...] ``` Kila kipengele cha alama kina: - **Jina** - **Sifa za uhusiano** (dhaifu, za ndani au za kimataifa): Alama ya ndani inaweza kufikiwa tu na programu yenyewe wakati alama za kimataifa zinashirikiwa nje ya programu. Kitu dhaifu ni mfano wa kazi ambayo inaweza kubadilishwa na nyingine tofauti. - **Aina**: NOTYPE (aina haijabainishwa), OBJECT (kibadilisha data cha kimataifa), FUNC (kazi), SECTION (sehemu), FILE (faili ya msimbo wa chanzo kwa ajili ya wadhibiti), TLS (kibadilisha cha ndani cha nyuzi), GNU_IFUNC (kazi isiyo ya moja kwa moja kwa ajili ya uhamasishaji) - **Sehemu** index ambapo iko - **Thamani** (anwani katika kumbukumbu) - **Ukubwa** ## Sehemu ya Kihisia ``` readelf -d lnstat Dynamic section at offset 0xfc58 contains 28 entries: Tag Type Name/Value 0x0000000000000001 (NEEDED) Shared library: [libc.so.6] 0x0000000000000001 (NEEDED) Shared library: [ld-linux-aarch64.so.1] 0x000000000000000c (INIT) 0x1088 0x000000000000000d (FINI) 0x2f74 0x0000000000000019 (INIT_ARRAY) 0x1fc48 0x000000000000001b (INIT_ARRAYSZ) 8 (bytes) 0x000000000000001a (FINI_ARRAY) 0x1fc50 0x000000000000001c (FINI_ARRAYSZ) 8 (bytes) 0x000000006ffffef5 (GNU_HASH) 0x338 0x0000000000000005 (STRTAB) 0x7f0 0x0000000000000006 (SYMTAB) 0x358 0x000000000000000a (STRSZ) 510 (bytes) 0x000000000000000b (SYMENT) 24 (bytes) 0x0000000000000015 (DEBUG) 0x0 0x0000000000000003 (PLTGOT) 0x1fe58 0x0000000000000002 (PLTRELSZ) 960 (bytes) 0x0000000000000014 (PLTREL) RELA 0x0000000000000017 (JMPREL) 0xcc8 0x0000000000000007 (RELA) 0xaa0 0x0000000000000008 (RELASZ) 552 (bytes) 0x0000000000000009 (RELAENT) 24 (bytes) 0x000000000000001e (FLAGS) BIND_NOW 0x000000006ffffffb (FLAGS_1) Flags: NOW PIE 0x000000006ffffffe (VERNEED) 0xa50 0x000000006fffffff (VERNEEDNUM) 2 0x000000006ffffff0 (VERSYM) 0x9ee 0x000000006ffffff9 (RELACOUNT) 15 0x0000000000000000 (NULL) 0x0 ``` Direktori ya NEEDED inaonyesha kwamba programu **inahitaji kupakia maktaba iliyoelezwa** ili kuendelea. Direktori ya NEEDED inakamilika mara tu **maktaba inayo shared inakuwa na kazi kamili na tayari** kwa matumizi. ## Mabadiliko Mchambuzi pia lazima ahamasishe utegemezi baada ya kuyapakia. Mabadiliko haya yanaonyeshwa katika jedwali la mabadiliko katika muundo wa REL au RELA na idadi ya mabadiliko inatolewa katika sehemu za dynamic RELSZ au RELASZ. ``` readelf -r lnstat Relocation section '.rela.dyn' at offset 0xaa0 contains 23 entries: Offset Info Type Sym. Value Sym. Name + Addend 00000001fc48 000000000403 R_AARCH64_RELATIV 1d10 00000001fc50 000000000403 R_AARCH64_RELATIV 1cc0 00000001fff0 000000000403 R_AARCH64_RELATIV 1340 000000020008 000000000403 R_AARCH64_RELATIV 20008 000000020010 000000000403 R_AARCH64_RELATIV 3330 000000020030 000000000403 R_AARCH64_RELATIV 3338 000000020050 000000000403 R_AARCH64_RELATIV 3340 000000020070 000000000403 R_AARCH64_RELATIV 3348 000000020090 000000000403 R_AARCH64_RELATIV 3350 0000000200b0 000000000403 R_AARCH64_RELATIV 3358 0000000200d0 000000000403 R_AARCH64_RELATIV 3360 0000000200f0 000000000403 R_AARCH64_RELATIV 3370 000000020110 000000000403 R_AARCH64_RELATIV 3378 000000020130 000000000403 R_AARCH64_RELATIV 3380 000000020150 000000000403 R_AARCH64_RELATIV 3388 00000001ffb8 000a00000401 R_AARCH64_GLOB_DA 0000000000000000 _ITM_deregisterTM[...] + 0 00000001ffc0 000b00000401 R_AARCH64_GLOB_DA 0000000000000000 __cxa_finalize@GLIBC_2.17 + 0 00000001ffc8 000f00000401 R_AARCH64_GLOB_DA 0000000000000000 stderr@GLIBC_2.17 + 0 00000001ffd0 001000000401 R_AARCH64_GLOB_DA 0000000000000000 optarg@GLIBC_2.17 + 0 00000001ffd8 001400000401 R_AARCH64_GLOB_DA 0000000000000000 stdout@GLIBC_2.17 + 0 00000001ffe0 001e00000401 R_AARCH64_GLOB_DA 0000000000000000 __gmon_start__ + 0 00000001ffe8 001f00000401 R_AARCH64_GLOB_DA 0000000000000000 __stack_chk_guard@GLIBC_2.17 + 0 00000001fff8 002e00000401 R_AARCH64_GLOB_DA 0000000000000000 _ITM_registerTMCl[...] + 0 Relocation section '.rela.plt' at offset 0xcc8 contains 40 entries: Offset Info Type Sym. Value Sym. Name + Addend 00000001fe70 000300000402 R_AARCH64_JUMP_SL 0000000000000000 strtok@GLIBC_2.17 + 0 00000001fe78 000400000402 R_AARCH64_JUMP_SL 0000000000000000 strtoul@GLIBC_2.17 + 0 00000001fe80 000500000402 R_AARCH64_JUMP_SL 0000000000000000 strlen@GLIBC_2.17 + 0 00000001fe88 000600000402 R_AARCH64_JUMP_SL 0000000000000000 fputs@GLIBC_2.17 + 0 00000001fe90 000700000402 R_AARCH64_JUMP_SL 0000000000000000 exit@GLIBC_2.17 + 0 00000001fe98 000800000402 R_AARCH64_JUMP_SL 0000000000000000 __libc_start_main@GLIBC_2.34 + 0 00000001fea0 000900000402 R_AARCH64_JUMP_SL 0000000000000000 perror@GLIBC_2.17 + 0 00000001fea8 000b00000402 R_AARCH64_JUMP_SL 0000000000000000 __cxa_finalize@GLIBC_2.17 + 0 00000001feb0 000c00000402 R_AARCH64_JUMP_SL 0000000000000000 putc@GLIBC_2.17 + 0 00000001feb8 000d00000402 R_AARCH64_JUMP_SL 0000000000000000 opendir@GLIBC_2.17 + 0 00000001fec0 000e00000402 R_AARCH64_JUMP_SL 0000000000000000 fputc@GLIBC_2.17 + 0 00000001fec8 001100000402 R_AARCH64_JUMP_SL 0000000000000000 snprintf@GLIBC_2.17 + 0 00000001fed0 001200000402 R_AARCH64_JUMP_SL 0000000000000000 __snprintf_chk@GLIBC_2.17 + 0 00000001fed8 001300000402 R_AARCH64_JUMP_SL 0000000000000000 malloc@GLIBC_2.17 + 0 00000001fee0 001500000402 R_AARCH64_JUMP_SL 0000000000000000 gettimeofday@GLIBC_2.17 + 0 00000001fee8 001600000402 R_AARCH64_JUMP_SL 0000000000000000 sleep@GLIBC_2.17 + 0 00000001fef0 001700000402 R_AARCH64_JUMP_SL 0000000000000000 __vfprintf_chk@GLIBC_2.17 + 0 00000001fef8 001800000402 R_AARCH64_JUMP_SL 0000000000000000 calloc@GLIBC_2.17 + 0 00000001ff00 001900000402 R_AARCH64_JUMP_SL 0000000000000000 rewind@GLIBC_2.17 + 0 00000001ff08 001a00000402 R_AARCH64_JUMP_SL 0000000000000000 strdup@GLIBC_2.17 + 0 00000001ff10 001b00000402 R_AARCH64_JUMP_SL 0000000000000000 closedir@GLIBC_2.17 + 0 00000001ff18 001c00000402 R_AARCH64_JUMP_SL 0000000000000000 __stack_chk_fail@GLIBC_2.17 + 0 00000001ff20 001d00000402 R_AARCH64_JUMP_SL 0000000000000000 strrchr@GLIBC_2.17 + 0 00000001ff28 001e00000402 R_AARCH64_JUMP_SL 0000000000000000 __gmon_start__ + 0 00000001ff30 002000000402 R_AARCH64_JUMP_SL 0000000000000000 abort@GLIBC_2.17 + 0 00000001ff38 002100000402 R_AARCH64_JUMP_SL 0000000000000000 feof@GLIBC_2.17 + 0 00000001ff40 002200000402 R_AARCH64_JUMP_SL 0000000000000000 getopt_long@GLIBC_2.17 + 0 00000001ff48 002300000402 R_AARCH64_JUMP_SL 0000000000000000 __fprintf_chk@GLIBC_2.17 + 0 00000001ff50 002400000402 R_AARCH64_JUMP_SL 0000000000000000 strcmp@GLIBC_2.17 + 0 00000001ff58 002500000402 R_AARCH64_JUMP_SL 0000000000000000 free@GLIBC_2.17 + 0 00000001ff60 002600000402 R_AARCH64_JUMP_SL 0000000000000000 readdir64@GLIBC_2.17 + 0 00000001ff68 002700000402 R_AARCH64_JUMP_SL 0000000000000000 strndup@GLIBC_2.17 + 0 00000001ff70 002800000402 R_AARCH64_JUMP_SL 0000000000000000 strchr@GLIBC_2.17 + 0 00000001ff78 002900000402 R_AARCH64_JUMP_SL 0000000000000000 fwrite@GLIBC_2.17 + 0 00000001ff80 002a00000402 R_AARCH64_JUMP_SL 0000000000000000 fflush@GLIBC_2.17 + 0 00000001ff88 002b00000402 R_AARCH64_JUMP_SL 0000000000000000 fopen64@GLIBC_2.17 + 0 00000001ff90 002c00000402 R_AARCH64_JUMP_SL 0000000000000000 __isoc99_sscanf@GLIBC_2.17 + 0 00000001ff98 002d00000402 R_AARCH64_JUMP_SL 0000000000000000 strncpy@GLIBC_2.17 + 0 00000001ffa0 002f00000402 R_AARCH64_JUMP_SL 0000000000000000 __assert_fail@GLIBC_2.17 + 0 00000001ffa8 003000000402 R_AARCH64_JUMP_SL 0000000000000000 fgets@GLIBC_2.17 + 0 ``` ### Static Relocations Ikiwa **programu imepakuliwa mahali tofauti** na anwani inayopendelea (kawaida 0x400000) kwa sababu anwani hiyo tayari inatumika au kwa sababu ya **ASLR** au sababu nyingine yoyote, uhamasishaji wa statiki **unarekebisha viashiria** ambavyo vilikuwa na thamani zikitarajia binary kupakuliwa katika anwani inayopendelea. Kwa mfano, sehemu yoyote ya aina `R_AARCH64_RELATIV` inapaswa kuwa na anwani iliyorekebishwa kwenye bias ya uhamasishaji pamoja na thamani ya kuongeza. ### Dynamic Relocations and GOT Uhamasishaji unaweza pia kurejelea alama ya nje (kama kazi kutoka kwa utegemezi). Kama kazi malloc kutoka libC. Kisha, mpakuwaji anapopakua libC katika anwani akichunguza mahali ambapo kazi ya malloc imepakuliwa, itaandika anwani hii katika jedwali la GOT (Global Offset Table) (linaloonyeshwa katika jedwali la uhamasishaji) ambapo anwani ya malloc inapaswa kufafanuliwa. ### Procedure Linkage Table Sehemu ya PLT inaruhusu kufanya uhusiano wa uvivu, ambayo inamaanisha kwamba ufumbuzi wa mahali pa kazi utafanywa wakati wa kwanza inapoombwa. Hivyo wakati programu inaita malloc, kwa kweli inaita mahali husika pa `malloc` katika PLT (`malloc@plt`). Wakati wa kwanza inapoitwa inatatua anwani ya `malloc` na kuihifadhi ili wakati wa pili `malloc` inapoitwa, anwani hiyo inatumika badala ya msimbo wa PLT. ## Program Initialization Baada ya programu kupakuliwa ni wakati wa kuendesha. Hata hivyo, msimbo wa kwanza unaotekelezwa **sio kila wakati kazi ya `main`**. Hii ni kwa sababu kwa mfano katika C++ ikiwa **kigezo cha kimataifa ni kitu cha darasa**, kitu hiki lazima kiwe **kimeanzishwa** **kabla** ya main kuendesha, kama katika: ```cpp #include // g++ autoinit.cpp -o autoinit class AutoInit { public: AutoInit() { printf("Hello AutoInit!\n"); } ~AutoInit() { printf("Goodbye AutoInit!\n"); } }; AutoInit autoInit; int main() { printf("Main\n"); return 0; } ``` Kumbuka kwamba hizi variables za kimataifa ziko katika `.data` au `.bss` lakini katika orodha `__CTOR_LIST__` na `__DTOR_LIST__` vitu vya kuanzisha na kuharibu vinahifadhiwa ili kufuatilia. Kutoka kwa msimbo wa C inawezekana kupata matokeo sawa kwa kutumia nyongeza za GNU: ```c __attributte__((constructor)) //Add a constructor to execute before __attributte__((destructor)) //Add to the destructor list ``` Kwa mtazamo wa mkusanyiko, ili kutekeleza vitendo hivi kabla na baada ya kazi ya `main` kutekelezwa, inawezekana kuunda kazi ya `init` na kazi ya `fini` ambazo zitarejelewa katika sehemu ya dynamic kama **`INIT`** na **`FIN`**. na zimewekwa katika sehemu za `init` na `fini` za ELF. Chaguo lingine, kama ilivyotajwa, ni kurejelea orodha **`__CTOR_LIST__`** na **`__DTOR_LIST__`** katika **`INIT_ARRAY`** na **`FINI_ARRAY`** katika sehemu ya dynamic na urefu wa hizi unatajwa na **`INIT_ARRAYSZ`** na **`FINI_ARRAYSZ`**. Kila kipengee ni kiashiria cha kazi ambacho kitaitwa bila hoja. Zaidi ya hayo, inawezekana pia kuwa na **`PREINIT_ARRAY`** yenye **viashiria** ambavyo vitatekelezwa **kabla** ya viashiria vya **`INIT_ARRAY`**. ### Agizo la Uanzishaji 1. Programu inawekwa kwenye kumbukumbu, mabadiliko ya kimataifa ya static yanaanzishwa katika **`.data`** na yasiyoanzishwa yanawekwa sifuri katika **`.bss`**. 2. **Mahitaji yote** ya programu au maktaba yanaanzishwa na **kuunganishwa kwa dynamic** kunatekelezwa. 3. Kazi za **`PREINIT_ARRAY`** zinafanywa. 4. Kazi za **`INIT_ARRAY`** zinafanywa. 5. Ikiwa kuna kipengee cha **`INIT`** kinaitwa. 6. Ikiwa ni maktaba, dlopen inamalizika hapa, ikiwa ni programu, ni wakati wa kuita **nukta halisi ya kuingia** (kazi ya `main`). ## Hifadhi ya Mitaa ya Thread (TLS) Zimefafanuliwa kwa kutumia neno muhimu **`__thread_local`** katika C++ au nyongeza ya GNU **`__thread`**. Kila thread itahifadhi eneo la kipekee kwa ajili ya variable hii hivyo ni thread pekee inayoweza kufikia variable yake. Wakati hii inatumika sehemu **`.tdata`** na **`.tbss`** zinatumika katika ELF. Ambazo ni kama `.data` (iliyowekwa) na `.bss` (siyo iliyowekwa) lakini kwa TLS. Kila variable itakuwa na kipengee katika kichwa cha TLS kinachoelezea ukubwa na ofset ya TLS, ambayo ni ofset itakayotumiwa katika eneo la data la ndani la thread. `__TLS_MODULE_BASE` ni alama inayotumika kurejelea anwani ya msingi ya hifadhi ya ndani ya thread na inaelekeza kwenye eneo katika kumbukumbu ambalo lina data zote za ndani za thread za moduli. {{#include ../../banners/hacktricks-training.md}}