Parameters are not pushed on to stack, those are kept in different registers, like ebx, ecx, edx, esi, edi. I want to know how control switches when int 0x80 occurs, from this interrupt instruction how the eip and ecs registers values are changed to point to kernel code in entry.S. In DOS I read that when "int" instruction is executed, control is passed to (interrupt number * 4) memory location, as each entry in interrupt table is of 4 bytes. Is it the same case with Linux architecture as well ? If we take it like that, then our control should be passed to (0x80 * 4) memory location, which is 512 (or in Hexa 0x200) memory location, but I found the point in entry.S, where control is transferred "ENTRY(system_call)", does not fall at this memory location. According to System.map file in boot drive (/boot/System.map) this code in entry.S falls at "c0109504" memory location (cat /boot/System.map | grep system_call) If anybody knows the reason of this, then please reply. Regards, Gaurav -----Original Message----- From: kernelnewbies-bounce@xxxxxxxxxxxx [mailto:kernelnewbies-bounce@xxxxxxxxxxxx] On Behalf Of Christophe Lucas Sent: Tuesday, July 27, 2004 1:23 PM To: kernelnewbies@xxxxxxxxxxxx Subject: Re: Switch from User space to Kernel space. Sanjay Kumar, Noida (sanjayku@xxxxxxxxxxxxxxxxx) wrote: > The inline assembley code is > making a system call ( int $0x80) > passing system call number (__NR_##name) and argument( arg1) it requires. > The value returned from the system call is obtained in __res variable > a and b denotes eax and ebx registers respectively. > Basically the inline assembly format is like > asm ( assembler template > : output operands > : input operands); hi, As I know, to switch from user to kernel land, parameters are push on stack and eax contains nr_syscall (number of the system call). Afterwards, an 0x80 int are generated: (int $0x80). Now you are in : linux/arch/i386/kernel/entry.S and syscall are choiced by eax register and kernel sys_ function is called. If I say some awful mistake, please correct me. I am here to learn :-) -- Amicalement/Regards Christophe Lucas - c.lucas@xxxxxxxxxxx - Registered User #271267 * GNU/Linux developer/network administrator * Membre du RotomaLUG (LUG de la région Rouennaise) (http://www.rotomalug.org) * http://odie.mcom.fr/~clucas/ -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
