Hello, On the PC ASLR will reduce the interest of calling function by direct litteral address.
But, for example, if you know for sure that the libc is loaded at address X and the function you want has offset Y within this lib, you could certainly call that function directly using this syntax. -------- This is used a lot in the NSPIRE calculator from Texas Instruments. Interesting entry points from the original OS were reverse engineered, and are used to define functions for use in custom software. Addresses differ according to the OS version, so there are mechanisms to choose the correct address. http://hackspire.unsads.com/wiki/index.php/Ndless_features_and_limitations#Syscalls (note: these are not real syscalls, since no part of the nspire os is running in system mode) ----- In TI calculators based on the 68k processor (ti92+ and such), we had a "rom call" table which was a table of function pointers. The base address of the tabme was stored at a known address, and the indexes in the table were associated to identical functions, so we could call a large quantity of pre-coded routines using a set of macros: /*C8h is the memory location that stores the address of the rom call table*/ #define __jmp_tbl (*(void***)0xC8) #define _rom_call_addr_concat(intindex,romindex) (__jmp_tbl [intindex]) #define _rom_call_concat(type,args,intindex,romindex) (*((type (* __ATTR_TIOS__) args) (__rom_call_addr_concat (intindex, romindex)))) #define _rom_call(type,args,index) (_rom_call_concat (type, args, 0x##index, _ROM_CALL_##index)) #define memcpy _rom_call(void*,(void*,const void*,long),26A) #define memmove _rom_call(void*,(void*,const void*,long),26B) #define memset _rom_call(void*,(void*,short,long),27C) #define sprintf _rom_call_attr(short,(char*,const char*,...),__attribute__((__format__(__printf__,2,3))),53) etc. I also see that the Z80 based ti calculators also have something like this with their "bcalls" http://wikiti.brandonw.net/index.php?title=84PCSE:OS:Include_File http://wikiti.brandonw.net/index.php?title=83Plus:BCALLs:5017 Regards Sébastien Lorquet Le 02/10/2014 13:28, 陳韋任 (Wei-Ren Chen) a écrit : >> Well, you know if you or someone else put it there. This is common for >> BIOS-like library functions that are already present in the memory. > > Thanks for your explanation. I have no experience on using BIOS-like > library, but I guess what you mean is some kind of library that > preloaded into memory at a fixed address? > > When talking about function call, I only know call by function name, > or call by a function pointer. Treating a memory address as function > is really new to me. This kind of usage only exists in microchip > enviroment, or I can reproduce it in my PC? Just curious. ;-) > > BR, > chenwj > ------------------------------------------------------------------------------ Meet PCI DSS 3.0 Compliance Requirements with EventLog Analyzer Achieve PCI DSS 3.0 Compliant Status with Out-of-the-box PCI DSS Reports Are you Audit-Ready for PCI DSS 3.0 Compliance? Download White paper Comply to PCI DSS 3.0 Requirement 10 and 11.5 with EventLog Analyzer http://pubads.g.doubleclick.net/gampad/clk?id=154622311&iu=/4140/ostg.clktrk _______________________________________________ Sdcc-user mailing list Sdcc-user@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/sdcc-user
