On Sunday 12 April 2009 19:30:33 Jamie Lokier wrote: > Mike Frysinger wrote: > > > It's easy but you need an asm wrapper for each architecture, as the > > > parent must not touch the stack before calling _exit. > > > > i'm aware of this which is why i used INTERNAL_SYSCALL() rather than > > calling the C library functions. those expand into the appropriate > > assembly for making a system call. > > I only see INTERNAL_SYSCALL on ARM, but perhaps I'm looking at an old > version of uclibc?
it should be implemented in most ports now in trunk. if a port doesnt, well it should fix that anyways. > You have to test the result of clone() before calling _exit(). How do > you guarantee the compiler inserts no memory writes in that sequence > using just INTERNAL_SYSCALL on all architectures? there is no guarantee of course, but i declare the storage of the return value of clone with "register", so that seems to be "good enough". i reviewed the disassembly on a few arches and they all look correct. just dont build with optimization turned off ;). the Blackfin assembly for example is: 18: a0 00 EXCPT 0x0; /* syscall(clone) */ 1a: ea 63 R2 = -0x3 (X); 1c: 08 30 R1 = R0; 1e: f8 67 R0 += -0x1; 20: 10 0a CC = R0 <= R2 (IU); 22: 03 14 IF !CC JUMP 0x28 <_daemon+0x28> (BP); 24: 08 68 P0 = 0x1 (X); 26: a0 00 EXCPT 0x0; /* syscall(exit) */ no stack usage by the parent -mike
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