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| en:docs:boot:freeldr:os2csm [2013/03/11 15:27] – created valerius | en:docs:boot:freeldr:os2csm [2014/05/21 21:13] (current) – external edit 127.0.0.1 | ||
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| - | == OS2CSM Idea == | + | ===== OS2CSM Idea ===== |
| Veit Kannegieser wrote a program, called os2csm. It was inspired by some DOS program, which modifies config.sys in memory. Os2csm installs itself in place of os2ldr, and renames os2ldr to os2ldr.bin. Os2csm hooks onto int 13h interrupt handler and analyzes the information read through int 13 routine. The config.sys file contains directives, analogous to C preprocessor directives, and each 512 bytes of config.sys file (each disk sector of config.sys) has a special comment with a special signature in it. The procedure, which hooks onto int 13h interrupt handler, checks each sector for these signatures, and if it finds them, it assumes that the config.sys file is being read. So, it substitutes preprocessor defines and patches config.sys on the fly. | Veit Kannegieser wrote a program, called os2csm. It was inspired by some DOS program, which modifies config.sys in memory. Os2csm installs itself in place of os2ldr, and renames os2ldr to os2ldr.bin. Os2csm hooks onto int 13h interrupt handler and analyzes the information read through int 13 routine. The config.sys file contains directives, analogous to C preprocessor directives, and each 512 bytes of config.sys file (each disk sector of config.sys) has a special comment with a special signature in it. The procedure, which hooks onto int 13h interrupt handler, checks each sector for these signatures, and if it finds them, it assumes that the config.sys file is being read. So, it substitutes preprocessor defines and patches config.sys on the fly. | ||