[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Qemu-devel] [PULL 0/9] Misc patches for QEMU 2.5-rc2 (2015-11-25)
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PULL 0/9] Misc patches for QEMU 2.5-rc2 (2015-11-25) |
Date: |
Thu, 26 Nov 2015 12:23:15 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0 |
On 26/11/2015 11:56, Peter Maydell wrote:
> On 26 November 2015 at 10:40, Paolo Bonzini <address@hidden> wrote:
>>
>>
>> On 26/11/2015 10:46, Peter Maydell wrote:
>>> I definitely don't think we should apply the -fwrapv patch yet;
>>> would you mind respinning this pullrequest without it?
>>
>> In what way does that patch make that thing worse?
>
> It makes a claim about the semantics that the compiler
> guarantees us which isn't currently valid. (Or
> alternatively, it's implicitly claiming that clang isn't
> a supported compiler, which isn't true.) I don't think
> we should document or rely on signed-shift semantics
But we are relying on them, and thus we should document them. Witness
the number of patches fixing so called "undefined" behavior. And those
patches are _dangerous_.
I can certainly remove the "as documented by the GCC manual" part and
the -fwrapv setting, but silencing -Wshift-negative-value and
documenting what we rely on should go in.
Paolo
> until we have the relevant documented promises from the
> compiler developers that that is what they are providing.
> (I'm happy that the gcc folks have provided those promises, they
> just need to actually document them in the -fwrapv option
> docs. The clang folks haven't replied yet so we don't know.)
- Re: [Qemu-devel] [PULL 2/9] QEMU does not care about left shifts of signed negative values, (continued)
- Re: [Qemu-devel] [PULL 2/9] QEMU does not care about left shifts of signed negative values, Peter Maydell, 2015/11/25
- Re: [Qemu-devel] [PULL 2/9] QEMU does not care about left shifts of signed negative values, Paolo Bonzini, 2015/11/25
- Re: [Qemu-devel] [PULL 2/9] QEMU does not care about left shifts of signed negative values, Peter Maydell, 2015/11/25
- Re: [Qemu-devel] [PULL 2/9] QEMU does not care about left shifts of signed negative values, Paolo Bonzini, 2015/11/25
- Re: [Qemu-devel] [PULL 2/9] QEMU does not care about left shifts of signed negative values, Peter Maydell, 2015/11/25
[Qemu-devel] [PULL 7/9] target-i386: kvm: Abort if MCE bank count is not supported by host, Paolo Bonzini, 2015/11/25
[Qemu-devel] [PULL 9/9] target-i386: kvm: Print warning when clearing mcg_cap bits, Paolo Bonzini, 2015/11/25
Re: [Qemu-devel] [PULL 0/9] Misc patches for QEMU 2.5-rc2 (2015-11-25), Peter Maydell, 2015/11/26
- Re: [Qemu-devel] [PULL 0/9] Misc patches for QEMU 2.5-rc2 (2015-11-25), Paolo Bonzini, 2015/11/26
- Re: [Qemu-devel] [PULL 0/9] Misc patches for QEMU 2.5-rc2 (2015-11-25), Peter Maydell, 2015/11/26
- Re: [Qemu-devel] [PULL 0/9] Misc patches for QEMU 2.5-rc2 (2015-11-25),
Paolo Bonzini <=
- Re: [Qemu-devel] [PULL 0/9] Misc patches for QEMU 2.5-rc2 (2015-11-25), Peter Maydell, 2015/11/26
- Re: [Qemu-devel] [PULL 0/9] Misc patches for QEMU 2.5-rc2 (2015-11-25), Markus Armbruster, 2015/11/26
- Re: [Qemu-devel] [PULL 0/9] Misc patches for QEMU 2.5-rc2 (2015-11-25), Peter Maydell, 2015/11/26
- Re: [Qemu-devel] [PULL 0/9] Misc patches for QEMU 2.5-rc2 (2015-11-25), Paolo Bonzini, 2015/11/26
Re: [Qemu-devel] [PULL 0/9] Misc patches for QEMU 2.5-rc2 (2015-11-25), Paolo Bonzini, 2015/11/26
Re: [Qemu-devel] [PULL 0/9] Misc patches for QEMU 2.5-rc2 (2015-11-25), Peter Maydell, 2015/11/26
Re: [Qemu-devel] [PULL 0/9] Misc patches for QEMU 2.5-rc2 (2015-11-25), Paolo Bonzini, 2015/11/26
Re: [Qemu-devel] [PULL 0/9] Misc patches for QEMU 2.5-rc2 (2015-11-25), Peter Maydell, 2015/11/26
Re: [Qemu-devel] [PULL 0/9] Misc patches for QEMU 2.5-rc2 (2015-11-25), Paolo Bonzini, 2015/11/26