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Re: timespec test failure on Linux/s390x

From: Bruno Haible
Subject: Re: timespec test failure on Linux/s390x
Date: Mon, 13 Sep 2021 00:44:23 +0200

Paul Eggert wrote:
> > I can't determine whether it's a GCC or a QEMU bug.
> Surely it is a QEMU bug, as QEMU isn't properly implementing the 
> z/Architecture Principles of Operation (POP).

Thanks; I didn't know about this document.

> Page 7-25 of the current 
> edition (SA22-7832-12) says that the AGR instruction treats its operands 
> as 64-bit signed binary integers, and sets condition code 3 (the 
> overflow flag) if the result overflows. You can get a copy of the POP 
> here (requires registration):
> https://www.ibm.com/support/pages/zarchitecture-principles-operation

The previous edition (available without registration at
http://publibfi.boulder.ibm.com/epubs/pdf/dz9zr011.pdf )
says the same thing.

> The patch you submitted to QEMU looks reasonable. However, there are 
> similar bugs in cc_calc_sub_32 and cc_calc_sub_64 that should also be 
> fixed.

Oh, indeed! I had looked at these functions and did not see the bug.
Reported at https://gitlab.com/qemu-project/qemu/-/issues/618 .


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