Re: mmap and PROT_WRITE
Jason Mawdsley writes: > Why can't I write to memory in the first case? > > Is there anyway I can implement writable but no readable memory? > > I read some where that there is no true write only memory do to the > limitations of x86. I think you must have read correctly -- your sample code runs fine (both cases) on FreeBSD/alpha. The same test program dumps core on FreeBSD/i386 Cheers, Drew To Unsubscribe: send mail to [EMAIL PROTECTED] with "unsubscribe freebsd-hackers" in the body of the message
Re: mmap and PROT_WRITE
Jason Mawdsley wrote: [ ... trying to distinguish between PROT_WRITE and PROT_READ|PROT_WRITE ... ] > Why can't I write to memory in the first case? > > Is there anyway I can implement writable but no readable memory? Yes. Use hardware manufactured by a vendor other than Intel, and which can support it. > I read some where that there is no true write only memory do to the > limitations of x86. Yes. And on 386, there's no write protection against protected mode writes at all, so you have to do dirty tricks to keep people from doing a "read" into a kernel address space in order to have the kernel. It's one of the reasons (besides /dev/slow^Wrandom) that the 386 is no longer supported in the GENERIC kernel. -- Terry To Unsubscribe: send mail to [EMAIL PROTECTED] with "unsubscribe freebsd-hackers" in the body of the message
mmap and PROT_WRITE
{
void * p = mmap( 0, 1024, PROT_WRITE, MAP_ANON, -1, 0 );
if ( p )
{
/*
* pukes and dies
* *((int*)(p)) = 5;
*/
}
}
{
void * p = mmap( 0, 1024, PROT_WRITE | PROT_READ, MAP_ANON, -1, 0 );
if ( p )
{
*((int*)(p)) = 5;
}
}
Why can't I write to memory in the first case?
Is there anyway I can implement writable but no readable memory?
I read some where that there is no true write only memory do to the
limitations of x86.
TIA
Jason Mawdsley ~ [EMAIL PROTECTED]
Software Designer ~ m_ a c a d a m i a nt e c h n o l o g i e s
"Software experts for the world's leading technology companies."
http://www.macadamian.com
Because software development cycles should not end in tragedy.
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