[Qemu-devel] Re: qemu-ppc fails to run clone with CLONE_VM, threaded programs, non-static programs

[Josh Triplett <josh@psas.pdx.edu>]

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Josh Triplett wrote:
> I'm attempting to run cross-compiled programs with qemu-ppc.  Basic
> statically-linked programs work perfectly.  However, if I attempt to run
> non-static programs or threaded programs, or if I attempt to call
> clone() with the CLONE_VM flag set, I get an invalid data memory access.
> 
> Threaded programs get an error when calling pthread_create, with an
> invalid data memory access at 0x00000018.  A simple test program using
> clone with CLONE_VM gets an invalid data memory access at 0x00000008.
> Non-static programs get an invalid data memory access at various
> addresses around 0x0de00000, before ever reaching main().

I worked with pbrook on #qemu to debug this issue.  The problem turns
out to be that qemu's do_fork function on PowerPC zeroes out r7-r31 in
the new CPU state structure after a clone, which it should not do, as
the child's registers should match the parent; it also does not zero
register r3, which holds the return value and should be zero in the
child.  I've prepared and attached a patch which should solve this problem.

- Josh Triplett

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diff -Naur qemu-0.7.0.orig/linux-user/syscall.c qemu-0.7.0/linux-user/syscall.c
--- qemu-0.7.0.orig/linux-user/syscall.c	2005-10-21 19:56:04.000000000 -0700
+++ qemu-0.7.0/linux-user/syscall.c	2005-10-21 20:02:20.000000000 -0700
@@ -1560,11 +1560,7 @@
         if (!newsp)
             newsp = env->gpr[1];
         new_env->gpr[1] = newsp;
-        { 
-            int i;
-            for (i = 7; i < 32; i++)
-                new_env->gpr[i] = 0;
-        }
+        new_env->gpr[3] = 0;
 #else
 #error unsupported target CPU
 #endif

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