* Re: [Qemu-devel] qemu-user mmap not thread-safe?
2007-06-19 14:04 ` Alexander Graf
@ 2007-06-20 9:32 ` Kirill A. Shutemov
0 siblings, 0 replies; 4+ messages in thread
From: Kirill A. Shutemov @ 2007-06-20 9:32 UTC (permalink / raw)
To: qemu-devel
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On [Tue, 19.06.2007 16:03], Alexander Graf wrote:
> Paul Brook wrote:
> > On Thursday 24 May 2007, Alexander Graf wrote:
> >
> >> Hi,
> >>
> >> while playing around with TLS on i386 i came across this problem which
> >> occurs even when no TLS is used at all. If two threads just malloc()
> >> memory all the time I get a segmentation fault after a short time. Might
> >> this be a serious bug?
> >>
> >
> > qemu is not even vaguely threadsafe.
> >
> > Paul
> >
> >
> >
> Hi,
>
> I somehow narrowed the problem down to x86_64. As soon as I use
> qemu-i386 on i386 or ppc the memory mapping tables are OK. When using
> x86_64 as host they are broken. Could this be a generic 64-bit host
> problem? I doubt that this actually has to do too much with the
> threading itself, because it works fine on other platforms.
On x86_64 mmap() sometimes return address above 4G. It is problem if target
system is 32-bit. I use attached patch to solve it.
--
Regards, Kirill A. Shutemov
+ Belarus, Minsk
+ Velesys LLC, http://www.velesys.com/
+ ALT Linux Team, http://www.altlinux.com/
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diff -uNr qemu-0.8.2.orig/linux-user/mmap.c qemu-0.8.2/linux-user/mmap.c
--- qemu-0.8.2.orig/linux-user/mmap.c 2007-01-16 16:05:33 +0200
+++ qemu-0.8.2/linux-user/mmap.c 2007-01-16 16:27:28 +0200
@@ -27,6 +27,10 @@
#include "qemu.h"
+#if !defined(MAP_32BIT)
+#define MAP_32BIT 0
+#endif
+
//#define DEBUG_MMAP
/* NOTE: all the constants are the HOST ones, but addresses are target. */
@@ -116,7 +120,7 @@
if (prot1 == 0) {
/* no page was there, so we allocate one */
ret = (long)mmap(host_start, qemu_host_page_size, prot,
- flags | MAP_ANONYMOUS, -1, 0);
+ flags | MAP_ANONYMOUS | MAP_32BIT, -1, 0);
if (ret == -1)
return ret;
prot1 = prot;
@@ -217,7 +221,8 @@
abort();
host_len = HOST_PAGE_ALIGN(len) + qemu_host_page_size - TARGET_PAGE_SIZE;
real_start = (long)mmap(g2h(real_start), host_len, PROT_NONE,
- MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+ MAP_PRIVATE | MAP_ANONYMOUS | MAP_32BIT
+ , -1, 0);
if (real_start == -1)
return real_start;
real_end = real_start + host_len;
@@ -234,7 +239,7 @@
host_offset = offset & qemu_host_page_mask;
host_len = len + offset - host_offset;
host_start = (long)mmap(real_start ? g2h(real_start) : NULL,
- host_len, prot, flags, fd, host_offset);
+ host_len, prot, flags | MAP_32BIT, fd, host_offset);
if (host_start == -1)
return host_start;
/* update start so that it points to the file position at 'offset' */
@@ -312,7 +317,7 @@
else
offset1 = offset + real_start - start;
ret = (long)mmap(g2h(real_start), real_end - real_start,
- prot, flags, fd, offset1);
+ prot, flags | MAP_32BIT, fd, offset1);
if (ret == -1)
return ret;
}
@@ -388,7 +393,7 @@
int prot;
/* XXX: use 5 args syscall */
- new_addr = (long)mremap(g2h(old_addr), old_size, new_size, flags);
+ new_addr = (long)mremap(g2h(old_addr), old_size, new_size, flags | MAP_32BIT);
if (new_addr == -1)
return new_addr;
new_addr = h2g(new_addr);
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