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Re: [Qemu-devel] Use Clang to compile Qemu?

From: David Turner
Subject: Re: [Qemu-devel] Use Clang to compile Qemu?
Date: Fri, 23 Dec 2011 14:07:53 +0100

Some parts of QEMU (the JIT) require the use of a global register variable to point to the "env" CPU state variable.

This feature is not supported by Clang (which is not very surprising given that it uses LLVM as its backend, and LLVM explicitely doesn't support this)

Until the JIT is modified to not require this anymore, it is very unlikely that Clang will be able to build QEMU.

There were previous discussions about such a change on this mailing list, but I believe nobody started working on that change because many feared it was a lot of work that would have a negative impact on performance (though I think it was all conjecture, i.e. no one really tried it and got any real data).

Please correct me if I'm wrong.

On Fri, Dec 23, 2011 at 1:00 PM, 陳韋任 <address@hidden> wrote:
Hi all,

 I am trying to build QEMU by using clang, but get error message below.

In file included from /z/tmp/chenwj/qemu-1.0/user-exec.c:21:
/z/tmp/chenwj/qemu-1.0/dyngen-exec.h:64:20: error: global register variables are not supported
register CPUState *env asm(AREG0);
1 warning and 1 error generated.

 Any idea on how to work around this? Thanks! :)


Wei-Ren Chen (陳韋任)
Computer Systems Lab, Institute of Information Science,
Academia Sinica, Taiwan (R.O.C.)
Tel:886-2-2788-3799 #1667
Homepage: http://people.cs.nctu.edu.tw/~chenwj

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