Interestingly enough if I compile with different optimization options
this goes from an illegal instruciton error to a bus error.
On 4/20/06, Russ Cox <[EMAIL PROTECTED]> wrote:
> [The only claim this has to being on topic is that
> I need an answer to make libthread work on OS X x86.
> That and it has to do with dynamic linking. Sorry.]
>
> In the gcc program below, the function runonstack uses
> some carefully crafted inline assembly to run the function fn
> on the given stack (the pointer passed in is the top of the stack).
> Because of the use of assembly, it is an x86-only program.
>
> It works great on Linux and on FreeBSD. On OS X, though,
> the function running on the alternate stack dies when it
> tries to call printf. A gdb session running the program
> is shown after the program.
>
> It's dying in the dynamic linker trying to resolve printf.
> If I call printf in main before calling runonstack, then printf
> no longer fails. However, if I then call exit(0) inside hello,
> then that fails, because exit isn't resolved yet.
>
> Thus, it appears that somehow the x86 OS X library routines
> cannot handle being called from an alternate stack.
> This just cannot be true. I thought everyone had already
> made that mistake and moved on.
>
> If anyone can either confirm that this program has no hope
> of working on OS X (that would be unfortunate) or can tell
> me what I need to do to make it work (that would be better!),
> I'd greatly appreciate it.
>
> As of right now, it appears that the plan9port CVS tree
> builds just fine on x86 OS X except that all the threaded
> programs crash due to this problem.
>
> Thanks for any help.
> Russ
>
>
>
> #include <stdio.h>
> #include <stdlib.h>
>
> char stack[1048576];
> char *state;
>
> void
> hello(void)
> {
> state = "calling printf";
> printf("hello, world\n");
> state = "done with printf";
> }
>
> void
> runonstack(void (*fn)(void), char *stack)
> {
> state = "in assembly";
> asm(
> "pushal\n"
> "movl 8(%ebp), %ebx\n" /* ebx = fn */
> "movl 12(%ebp), %eax\n" /* ecx = stack */
> "xchgl %esp, %eax\n"
> "pushl %eax\n"
> "call *%ebx\n"
> "popl %esp\n"
> "popal\n"
> );
> state = "out of assembly";
> }
>
> int
> main(int argc, char **argv)
> {
> runonstack(hello, stack+sizeof stack);
> }
>
> ---
>
> $ gdb a.out
> GNU gdb 6.1-20040303 (Apple version gdb-437) (Fri Jan 13 18:45:48 GMT 2006)
> Copyright 2004 Free Software Foundation, Inc.
> GDB is free software, covered by the GNU General Public License, and you are
> welcome to change it and/or distribute copies of it under certain conditions.
> Type "show copying" to see the conditions.
> There is absolutely no warranty for GDB. Type "show warranty" for details.
> This GDB was configured as "i386-apple-darwin"...Reading symbols for shared
> libraries .. done
>
> (gdb) run
> Starting program: /Users/rsc/a.out
> Reading symbols for shared libraries . done
>
> Program received signal EXC_BAD_INSTRUCTION, Illegal instruction/operand.
> 0x8fe136e4 in __dyld_stub_binding_helper_interface ()
> (gdb) print (char*)state
> $1 = 0x1fa8 "calling printf"
> (gdb) quit
> The program is running. Exit anyway? (y or n) y
> $
>
>
