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Re^2: C-like Pointers

by DerHartmut (Novice)
on Nov 16, 2009 at 03:34 UTC ( #807363=note: print w/ replies, xml ) Need Help??


in reply to Re: C-like Pointers
in thread C-like Pointers

Thank you for your answer (and either thank to the others) :D

I know the fact, that C can only access virtual memory, I choosed the easier term "RAM" for people which don't know about Paging and stuff.

My real problem is to solve the following problem:

A buddy wrote a program in C which loads a ELF-kernel and execute it. I (I'm either a C progammer and OS-developer) wanted to write the same program in Perl, just for fun. The biggest problem is to access a virtual address within the process' memoryspace and using pointers to these addresses. I have to write this line:

krnl = mmap((void *)0x78000000, lof, PROT_READ, MAP_PRIVATE | MAP_FIXE +D, fileno(kernel), 0);

In Perl. My (not working) solution is:

$mapped_kernel = syscall(\&SYS_mmap, $address, $kernel_size, $page_rea +d, $map_private | $map_fixed, fileno(KERNEL), 0);

where syscall() and \&SYS_mmap are functions/references to functions from syscall.h (converted to .ph via h2ph), $kernel_size, $page_read, $map_private and $map_fixed simple integer-values, KERNEL the filehandle to the loaded kernel and $address the pointer to the address.

In short words, I want to do (void*)0x78000000 in Perl, a pointer to a address defiend by myself (without the help of C :-P). I've searched CPAN for XS and pointers but did not found anything related to my problem (or I was too stupid to find it ^^).


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Re^3: C-like Pointers
by snoopy (Deacon) on Nov 16, 2009 at 05:11 UTC
    In short words, I want to do (void*)0x78000000 in Perl, a pointer to a address defiend by myself (without the help of C :-P). I've searched CPAN for XS and pointers but did not found anything related to my problem

    Did you come across Sys::Mmap's hardwire() method in your travels?

    Just reading the synopsis for this function:

           hardwire(VARIABLE, ADDRESS, LENGTH)
               Specifies the address in memory of a variable, possibly within a
               region you've "mmap()"ed another variable to. You must use the same
               precautions to keep the variable from being reallocated, and use
               "substr()" with an exact length. If you "munmap()" a region that a
               "hardwire()"ed variable lives in, the "hardwire()"ed variable will
               not automatically be "undef"ed. You must do this manually.
    
    ..and thought it just might be of use. Maybe try:
    use Sys::Mmap; # ... Sys::Mmap::hardwire($address, 0x78000000, $kernel_size);
      Great!

      That's extactly that I searched for. Thank very very very much! It does work now :D

      And many thanks to the others for their answers!

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