Date: Wed, 10 Jan 2007 01:22:50 -0500 (EST) From: "darran kartaschew" <chewy509@lycos.com> To: <freebsd-hackers@freebsd.org> Subject: sbrk vs mmap Message-ID: <20070110012250.HM.0000000000000G0@chewy509.bos-mail-wwl8.lycos.com>
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Hi Guys,
I'm having some issues with rewriting a simple malloc() function to be
with FreeBSD (AMD64). This is part of porting an application from
Linux
to FreeBSD.
After pulling my hair out for a while, I've found that the sbrk()
system call just returns "45 - Operation Not Supported" error,
irrespective of the parameters passed to it. (I've found the source
for sbrk() and see that it's not implemented).
So I decided to try using mmap() instead. All memory allocations don't
have to be continuous, so mmap() will suffice. The problem is I'm
getting an invalid file handle error? According to the man page, if
you
use MAP_ANON you're just allocating a block of memory without linking
to a file, and a handle of -1 should be supplied... Any way code is as
follows:
memInit:
mov r4, 0 ; don't care where the memory is allocated
mov r5, 1048576 ; alloc 1MB
mov r3, 3 ; RW access to memory
mov r2, 4096 ; MAP_ANON - not a file
mov r8d, -1 ; -1 for file handle if using MAP_ANON
mov r9, 0 ; ignored for MAP_ANON
mov r0, 197 ; mmap();
syscall
mov qword [_mmap], r0 ; save address so we can release it on exit;
ret
It fails with an EBADF (9) ; Bad File Descriptor error...
Note: r0 = rax, r1 = rbx, r2 = rcx, r3 = rdx, r4 = rdi, r5 = rsi, r6 =
rbp, r7 = rsp. Various parameters for mmap() are found in mman.h>.
So does anyone have an example of a working call to mmap() or tell me
what's wrong with the above code?
I've done up a test C program that simple calls mmap(), after
tracing through the compiled C program using gdb I can't see that
I'm doing anything different to what gcc/glibc are doing? (except
the macro expansion that's in libc which adds an additional
0 to the top of the stack).
PS. FASM 1.66 running on FreeBSD 6.1 (AMD64).
PPS. This is NOT a homework assignment! (tm) :P
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