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[Qemu-devel] [PULL 17/43] exec.c: Don't accidentally sign-extend 4-byte

From: Peter Maydell
Subject: [Qemu-devel] [PULL 17/43] exec.c: Don't accidentally sign-extend 4-byte loads in subpage_read()
Date: Fri, 15 Jun 2018 15:24:55 +0100

In subpage_read() we perform a load of the data into a local buffer
which we then access using ldub_p(), lduw_p(), ldl_p() or ldq_p()
depending on its size, storing the result into the uint64_t *data.
Since ldl_p() returns an 'int', this means that for the 4-byte
case we will sign-extend the data, whereas for 1 and 2 byte
reads we zero-extend it.

This ought not to matter since the caller will likely ignore values in
the high bytes of the data, but add a cast so that we're consistent.

Signed-off-by: Peter Maydell <address@hidden>
Reviewed-by: Richard Henderson <address@hidden>
Message-id: address@hidden
 exec.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/exec.c b/exec.c
index 9cbba6adcd3..90b47cde7b1 100644
--- a/exec.c
+++ b/exec.c
@@ -2747,7 +2747,7 @@ static MemTxResult subpage_read(void *opaque, hwaddr 
addr, uint64_t *data,
         *data = lduw_p(buf);
         return MEMTX_OK;
     case 4:
-        *data = ldl_p(buf);
+        *data = (uint32_t)ldl_p(buf);
         return MEMTX_OK;
     case 8:
         *data = ldq_p(buf);

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