> 2007/8/21, Yuriy Tsibizov <[EMAIL PROTECTED]>: > > 2007/8/20, Kostik Belousov <[EMAIL PROTECTED]>: > > > On Sat, Aug 18, 2007 at 02:01:26PM +0400, Yuriy Tsibizov wrote: > > > > I'm trying to get user-mode Linux to run under FreeBSD Linux emulation > > > > (on > > > > i386). > > > > > > > > User-mode Linux in it's start-up tests tries to modify syscall number > > > > (to be > > > > called by kernel) on-the-fly > > > > (http://fxr.watson.org/fxr/source/arch/um/os-Linux/start_up.c?v=linux-2.6). > > > > It forks a child thread that stops > > > > (using SIGSTOP), calls getpid() (that will be intercepted by parent > > > > thread > > > > using PTRACE_SYSCALL) > > > > and return some value based on getpid() results. Main thread waits for > > > > SIGSTOP in child process and > > > > enables PTRACE_SYSCALL (I have some code that implements it. It makes > > > > some > > > > incompatible changes > > > > to PT_SYSCALL that will break FreeBSD applications, but works for Linux > > > > apps). When main thread > > > > catches SIGTRAP (generated by ptrace) it tries to modify EAX of child > > > > thread > > > > (with PTRACE_PEEKUSR > > > > and PTRACE_POKEUSR) to replace getpid syscall with getppid. > > > > > > > > is it possible to get updated EAX (and other registers as well) in > > > > syscall(...) after ptracestop(...) in PTRACESTOP_SC(...) returns? > > > > > > > > Hope for your help, > > > > > > > > Yuriy. > > > > > > If I understand right what you want, I doubt that existing code would > > > allow you to change syscall number in debugger process for debuggee. > > > You shall look at the sys/i386/i386/trap.c, syscall() function [adjust > > > as needed for other arches]. It calculates callp before doing > > > PTRACESTOP_SC, > > > as well as copies the syscall arguments into the kernel address space. > > > > Yes, I know this. I'm going to recalculate callp after PTRACESTOP_SC. > > And, there will be no need to copyin from user space -- all syscalls > > parameters are passed in registers (it will be used only for processes > > running under Linux emulation). > Updated registers are available via *frame. > > With some hacks (some return codes needed by user-mode Linux are > hardcoded into kernel) it loads: [...] > I'll need two more flags in p_stops to add two optios: > - respect PTRACE_(OLD)SETOPTIONS PTRACE_O_TRACESYSGOOD (generate > SIGTRAP | 0x80 instead of plain SIGTRAP) > - use Linux PTRACE_SYSCALL conventions (clear S_PT_SCE and S_PT_SCX in > PTRACESTOP_SC) > to make it more than just a set of hacks to run single program. > > PTRACE_(PEEK|POKE)USR seems to need small rewrite too.
patch (against -CURRENT) is available on http://chibis.persons.gfk.ru/linux/ptrace.diff You will need to rebuild both kernel an linux module. Yuriy. _______________________________________________ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to "[EMAIL PROTECTED]"