Jon and I have encountered a strange issue when using VirtualBox with 64
bits Linux hosts: the monotonic counter is not monotonic, with both 32 and
64 bits Linux guest systems.
The attached program (compile with "gcc -O2 -o t t.c -lrt") gives an error
when executed onto the guest system with the following configurations:
- Host: 64 bits Linux 2.6.29 x86_64 + VirtualBox 3.0.2, Guest: 32 bits
Linux 2.6.32 i686
- Host: 64 bits Linux 2.6.32 x86_64 + VirtualBox 3.1.4, Guest: 32 bits
Linux 2.6.32 x86_64
The monotonic timer jumps backwards in time, causing a critical error in
Factor.
I've implemented the following stupid hack that can be pulled from "git://
git.rfc1149.net/factor.git for-slava":
--- a/vm/run.cpp
+++ b/vm/run.cpp
@@ -16,7 +16,8 @@ void factor_vm::primitive_system_micros()
void factor_vm::primitive_nano_count()
{
u64 nanos = nano_count();
- if(nanos < last_nano_count) critical_error("Monotonic counter
decreased",0);
+ if(nanos < last_nano_count)
+ nanos = last_nano_count + 1;
last_nano_count = nanos;
ctx->push(from_unsigned_8(nanos));
}
This does not seem to cause any trouble for Factor itself as the correction
is a one-time shot every time the problem occurs, and lets us use Factor in
VirtualBox with a 64 bits host. This should not change anything for systems
functioning correctly (the test program does not exhibit the bogus behaviour
when executed directly onto the host system).
Sam
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