Date: Thu, 11 Jan 2007 22:46:48 -0800 From: Suleiman Souhlal <ssouhlal@FreeBSD.org> To: darran kartaschew <chewy509@lycos.com> Cc: freebsd-hackers@freebsd.org Subject: Re: sbrk vs mmap Message-ID: <45A72ED8.8070402@FreeBSD.org> In-Reply-To: <20070110012250.HM.0000000000000G0@chewy509.bos-mail-wwl8.lycos.com> References: <20070110012250.HM.0000000000000G0@chewy509.bos-mail-wwl8.lycos.com>
next in thread | previous in thread | raw e-mail | index | archive | help
darran kartaschew wrote: > 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 I think you are missing a parameter. mmap (as well as pwrite, lseek, truncate and ftruncate), has a "hidden" parameter just before the offset that is ignored, due to a bug in ancient GCC versions. So, basically, you should also push a 0 on the stack. Take a look at src/sys/libc/sys/mmap.c . I have a patch to remove this useless argument, but haven't committed it yet. -- Suleiman
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?45A72ED8.8070402>