From: Renzo Davoli <renzo@cs.unibo.it>
To: LKML <linux-kernel@vger.kernel.org>, Jeff Dike <jdike@addtoit.com>
Subject: [PATCH] UML on UML breaks when testing SYSEMU
Date: Mon, 2 Feb 2009 14:22:16 +0100 [thread overview]
Message-ID: <20090202132215.GH28208@cs.unibo.it> (raw)
It is currently impossible to run a user-mode linux machine inside another user-mode
linux (UML on UML).
This is the output of a broken attempt:
$ ./linux mem=256m ubd0=cow
Locating the bottom of the address space ... 0x0
Locating the top of the address space ... 0xc0000000
Core dump limits :
soft - 0
hard - NONE
Checking that ptrace can change system call numbers...OK
Checking ptrace new tags for syscall emulation...unsupported
Checking syscall emulation patch for ptrace...check_sysemu : expected SIGTRAP, got status = 256
$
The problem is the following:
PTRACE_SYSCALL/SINGLESTEP is currently managed inside arch_ptrace for ARCH=um.
PTRACE_SYSEMU/SUSEMU_SINGLESTEP is not captured in arch_ptrace's switch, therefore
it is erroneously passed back to ptrace_request (in kernel/ptrace).
This simple patch simply forces ptrace to return an error on PTRACE_SYSEMU/SUSEMU_SINGLESTEP
as it is unsupported on ARCH=um, and fixes the problem.
Signed-off-by: Renzo Davoli <renzo@cs.unibo.it>
---
diff -Naur linux-2.6.28.2/arch/um/kernel/ptrace.c linux-2.6.28.2-umluml/arch/um/kernel/ptrace.c
--- linux-2.6.28.2/arch/um/kernel/ptrace.c 2009-01-25 01:42:07.000000000 +0100
+++ linux-2.6.28.2-umluml/arch/um/kernel/ptrace.c 2009-02-02 14:01:52.000000000 +0100
@@ -64,6 +64,11 @@
ret = poke_user(child, addr, data);
break;
+ case PTRACE_SYSEMU:
+ case PTRACE_SYSEMU_SINGLESTEP:
+ ret=-EIO;
+ break;
+
/* continue and stop at next (return from) syscall */
case PTRACE_SYSCALL:
/* restart after signal. */
reply other threads:[~2009-02-02 13:42 UTC|newest]
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