Re: [Qemu-devel] [PATCH] SPARC target : Fix carry flagupdate inaddxcc and subxc

[Blue Swirl]

> As far as the V flag is concerned, mmm, I'm not really sure whether we 
> should
> change something in the sparc code. If we compare to the arm code, we don't
> take into account the fact that the carry flag is set before.
>
> We'd probably need some extensive tests and their associated expected 
> results.

I made a small test program (attached) to test the addx instruction. The 
program calculates the sum of two 64-bit values, given on the command line 
as 32-bit lower and upper parts.  Native system produces following:
$ ./addx -1 -1 0x80000000 -1
ffffffffffffffff + ffffffff80000000 = ffffffff7fffffff, NZVC: 9
while unpatched Qemu the following:
$ qemu-sparc ./addx -1 -1 0x80000000 -1
ffffffffffffffff + ffffffff80000000 = ffffffff7fffffff, NZVC: 8

So the carry flag not set. When your patch is applied, the output is 
identical:
ffffffffffffffff + ffffffff80000000 = ffffffff7fffffff, NZVC: 9

I couldn't think of a combination of values that would set the V flag when 
there is also a carry from the 32-bit addition, any suggestions?

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addx.c
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