Thank you Pei, I'm currently following a tutorial on asm programming on linux On Oct 8, 2010, at 4:30 AM, Pei Lin wrote: > 2010/10/8 Juan Rafael Garcia Blanco <jgblanco.mail@xxxxxxxxx>: >> Well, I think it applies to all architectures, but I'm not sure, so take >> with care. Also, I think this is something everybody knows, sorry. >> The OS is mapped in every process address space, but its pages are protected >> (check out this http://www.logix.cz/michal/doc/i386/chp05-02.htm#F-05-10). A >> process cannot jump to a kernel address, because the process executes in >> user mode and kernel addresses are therefore protected from being executed >> by a user process. Then, a system call occurs and the kernel starts >> executing through an interrupt (the famous 0x80 vector number). > I think you are just confused by the parameters how to deliver to the > kernel space. > Because system call code runs in the kernel space and caller runs in > the user space, they use the different the > stack. On i386, the parameters of a system call are transported via > registers. The system call number goes into %eax, the first parameter > in %ebx, the second in %ecx, the third in %edx, the fourth in %esi, > the fifth in %edi, the sixth in %ebp. Parameters more than six, there > will be on register to save the address of the structure in the user > space, and in the system call routine will copy the parameters into > the kernel stack. > > The book <<Understanding the Linux Kernel By Daniel Pierre Bovet, > Marco Cesatí>> will give you more details. > http://books.google.com.hk/books?id=cbbMrRNiC4cC&pg=PT618&dq=system+call+parameter&hl=en&ei=AH-uTIbmBoayvgPOotndBg&sa=X&oi=book_result&ct=result&resnum=1&ved=0CCgQ6AEwAA#v=onepage&q=system%20call%20parameter&f=false > >> The active >> address space is the caller one, but now, since the kernel executes in >> privileged, any address of any page can be reached. The kernel can throw to >> the bus addresses from user space, cause it is actually using the process >> address space. >> I was confused mostly because I thought the kernel as a process, and I >> didn't remember how a page table entry looks like. Besides, I have learnt >> something: during an interrupt from an external device for example, the >> kernel cannot use addresses from any user process memory map, because the >> current address space may not be the correct one. >> Thank you, and sorry for my English >> On Oct 7, 2010, at 6:38 PM, hiren panchasara wrote: >> >> >> On Thu, Oct 7, 2010 at 9:28 AM, Juan Rafael Garcia Blanco >> <jgblanco.mail@xxxxxxxxx> wrote: >>> >>> Hi, it has just been solved, thank you >> >> Would you care to share? >> >> Thanks. >>> >>> On Oct 7, 2010, at 5:55 PM, Juan Rafael Garcia Blanco wrote: >>> >>>> Hi. >>>> During the boot process, Linux is loaded in main memory. When a system >>>> call is done, the OS executes again. If the system call is accompanied by >>>> some parameter, which is an address of the user process memory map, how can >>>> the kernel access that variable which is in user process memory map? I mean, >>>> when the kernel fires up an address, how is it translated? I can't find an >>>> answer to my question in books nor in the internet. >>>> >>>> Thank you very much >>> >>> >>> -- >>> To unsubscribe from this list: send an email with >>> "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx >>> Please read the FAQ at http://kernelnewbies.org/FAQ >>> >> >> >> > > > > -- > Best Regards > Lin -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
