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Re: [Qemu-devel] [PATCH] cpu-all.h: Don't accidentally sign extend in g2

From: Anthony Liguori
Subject: Re: [Qemu-devel] [PATCH] cpu-all.h: Don't accidentally sign extend in g2h()
Date: Mon, 12 Mar 2012 21:00:33 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:10.0.2) Gecko/20120216 Thunderbird/10.0.2

On 03/09/2012 08:33 AM, Peter Maydell wrote:
Cast the argument of the g2h() macro to a target_ulong so that
it isn't accidentally sign-extended if it is a signed 32 bit
type and long is a 64 bit type. In particular, this fixes a
bug where it would return the wrong value for 32 bit guests
on 64 bit hosts when passed in one of the arg* values from
do_syscall() [which are all abi_long and thus signed types].
This could result in spurious failure of mlock(), among others.

Signed-off-by: Peter Maydell<address@hidden>

Applied.  Thanks.


Anthony Liguori

This should be committed before Alex's patch to make mmap allocate
downwards (http://patchwork.ozlabs.org/patch/144476/) because that
hugely increases the chances that g2h will get passed a pointer
that has the high bit set.

  cpu-all.h |    2 +-
  1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/cpu-all.h b/cpu-all.h
index 80e6d42..a174532 100644
--- a/cpu-all.h
+++ b/cpu-all.h
@@ -197,7 +197,7 @@ extern unsigned long reserved_va;

  /* All direct uses of g2h and h2g need to go away for usermode softmmu.  */
-#define g2h(x) ((void *)((unsigned long)(x) + GUEST_BASE))
+#define g2h(x) ((void *)((unsigned long)(target_ulong)(x) + GUEST_BASE))

  #define h2g_valid(x) 1

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