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Re: chacha20-s390 broken in 8.2.0 in TCG on s390x

From: Philippe Mathieu-Daudé
Subject: Re: chacha20-s390 broken in 8.2.0 in TCG on s390x
Date: Wed, 3 Jan 2024 12:53:59 +0100
User-agent: Mozilla Thunderbird 
Hi Richard,

On 3/1/24 09:54, Michael Tokarev wrote:

03.01.2024 03:22, Richard Henderson wrote:

On 12/22/23 01:51, Michael Tokarev wrote:

...

git bisect points to this commit:

commit ab84dc398b3b702b0c692538b947ef65dbbdf52f
Author: Richard Henderson <richard.henderson@linaro.org>
Date:   Wed Aug 23 23:04:24 2023 -0700

     tcg/optimize: Optimize env memory operations

So far, this seems to work on amd64 host, but fails on s390x host -
where this has been observed so far.  Maybe it also fails in some
other combinations too, I don't yet know.  Just finished bisecting
it on s390x.


I haven't been able to build a reproducer for this.
Have you an image or kernel you can share?


Sure.
Here's my actual testing "image": http://www.corpit.ru/mjt/tmp/s390x-chacha.tar.gz
It contains vmlinuz and initrd - generated on a debian s390x system using standard 
debian tools.

Actual command line I used when doing bisection:
 ~/qemu/b/qemu-system-s390x -append "root=/dev/vda rw" -nographic -smp 2 -drive format=raw,file=vmlinuz,if=virtio -no-user-config -m 1G -kernel vmlinuz -initrd initrd -snapshot 

I had a quick look at the reproducer and reduced the code
area to:

void tcg_optimize(TCGContext *s)
{
    ...
        switch (opc) {
        case INDEX_op_ld_vec:
            done = fold_tcg_ld_memcopy(&ctx, op);


static bool fold_tcg_ld_memcopy(OptContext *ctx, TCGOp *op)
{
    ...
    if (src && src->base_type == type) {
        return tcg_opt_gen_mov(ctx, op, temp_arg(dst), temp_arg(src));
    }
static bool tcg_opt_gen_mov(OptContext *ctx, TCGOp *op, TCGArg dst, TCGArg src) 
{
    ...
    switch (ctx->type) {
    case TCG_TYPE_V128:
        new_op = INDEX_op_mov_vec;


By disabling this optimization, the test succeeds.

Looking at commit 4caad79f8d ("tcg/s390x: Support 128-bit load/store")
and remembering the constraints change on PPC LQ in
https://lore.kernel.org/qemu-devel/20240102013456.131846-1-richard.henderson@linaro.org/
I wondered if LPQ constraints are correct, but I disabled
TCG_TARGET_HAS_qemu_ldst_i128 and the bug persists (so
re-enabled).

Then disabling TCG_TARGET_HAS_v64 and TCG_TARGET_HAS_v128 the bug
disappears.

The problematic chacha20 guest code could be:

Restarting code generation with smaller translation block (max 86 insns)
----------------
IN:
0x3ff80025a62:  eb67 f030 0024  stmg     %r6, %r7, 0x30(%r15)
0x3ff80025a68:  a719 ff60       lghi     %r1, -0xa0
0x3ff80025a6c:  b904 000f       lgr      %r0, %r15
0x3ff80025a70:  41f1 f000       la       %r15, 0(%r1, %r15)
0x3ff80025a74:  e300 f000 0024  stg      %r0, 0(%r15)
0x3ff80025a7a:  c070 0000 12c3  larl     %r7, -0x7ffd8000
0x3ff80025a80:  a708 000a       lhi      %r0, 0xa
0x3ff80025a84:  e789 5000 0c36  .byte    0xe7, 0x89, 0x50, 0x00, 0x0c, 0x36
0x3ff80025a8a:  e7a0 6000 0806  .byte    0xe7, 0xa0, 0x60, 0x00, 0x08, 0x06
0x3ff80025a90:  e7bf 7000 4c36  .byte    0xe7, 0xbf, 0x70, 0x00, 0x4c, 0x36
0x3ff80025a96:  e70b 0000 0456  .byte    0xe7, 0x0b, 0x00, 0x00, 0x04, 0x56
0x3ff80025a9c:  e718 0000 0456  .byte    0xe7, 0x18, 0x00, 0x00, 0x04, 0x56
0x3ff80025aa2:  e74b 0000 0456  .byte    0xe7, 0x4b, 0x00, 0x00, 0x04, 0x56
0x3ff80025aa8:  e758 0000 0456  .byte    0xe7, 0x58, 0x00, 0x00, 0x04, 0x56
0x3ff80025aae:  e78b 0000 0456  .byte    0xe7, 0x8b, 0x00, 0x00, 0x04, 0x56
0x3ff80025ab4:  e798 0000 0456  .byte    0xe7, 0x98, 0x00, 0x00, 0x04, 0x56
0x3ff80025aba:  e7cb 0000 0456  .byte    0xe7, 0xcb, 0x00, 0x00, 0x04, 0x56
0x3ff80025ac0:  e7d8 0000 0456  .byte    0xe7, 0xd8, 0x00, 0x00, 0x04, 0x56
0x3ff80025ac6:  e70b 0000 0c56  .byte    0xe7, 0x0b, 0x00, 0x00, 0x0c, 0x56
0x3ff80025acc:  e718 0000 0c56  .byte    0xe7, 0x18, 0x00, 0x00, 0x0c, 0x56
0x3ff80025ad2:  e74b 0000 0c56  .byte    0xe7, 0x4b, 0x00, 0x00, 0x0c, 0x56
0x3ff80025ad8:  e758 0000 0c56  .byte    0xe7, 0x58, 0x00, 0x00, 0x0c, 0x56
0x3ff80025ade:  e73a 0000 0456  .byte    0xe7, 0x3a, 0x00, 0x00, 0x04, 0x56
0x3ff80025ae4:  e77a c000 26f3  .byte    0xe7, 0x7a, 0xc0, 0x00, 0x26, 0xf3
0x3ff80025aea:  e7ba d000 26f3  .byte    0xe7, 0xba, 0xd0, 0x00, 0x26, 0xf3
0x3ff80025af0:  e7fa e000 26f3  .byte    0xe7, 0xfa, 0xe0, 0x00, 0x26, 0xf3
0x3ff80025af6:  e73b d000 2af3  .byte    0xe7, 0x3b, 0xd0, 0x00, 0x2a, 0xf3
0x3ff80025afc:  e77b e000 2af3  .byte    0xe7, 0x7b, 0xe0, 0x00, 0x2a, 0xf3
0x3ff80025b02:  e729 0000 0456  .byte    0xe7, 0x29, 0x00, 0x00, 0x04, 0x56
0x3ff80025b08:  e769 0000 0456  .byte    0xe7, 0x69, 0x00, 0x00, 0x04, 0x56
0x3ff80025b0e:  e7a9 0000 0456  .byte    0xe7, 0xa9, 0x00, 0x00, 0x04, 0x56
0x3ff80025b14:  e7e9 0000 0456  .byte    0xe7, 0xe9, 0x00, 0x00, 0x04, 0x56
0x3ff80025b1a:  e729 0000 0c56  .byte    0xe7, 0x29, 0x00, 0x00, 0x0c, 0x56
0x3ff80025b20:  e769 0000 0c56  .byte    0xe7, 0x69, 0x00, 0x00, 0x0c, 0x56
0x3ff80025b26:  e7c7 0000 0856  .byte    0xe7, 0xc7, 0x00, 0x00, 0x08, 0x56
0x3ff80025b2c:  e7db 0000 0856  .byte    0xe7, 0xdb, 0x00, 0x00, 0x08, 0x56
0x3ff80025b32:  e7ef 0000 0856  .byte    0xe7, 0xef, 0x00, 0x00, 0x08, 0x56
0x3ff80025b38:  e700 1000 20f3  .byte    0xe7, 0x00, 0x10, 0x00, 0x20, 0xf3
0x3ff80025b3e:  e744 5000 20f3  .byte    0xe7, 0x44, 0x50, 0x00, 0x20, 0xf3
0x3ff80025b44:  e788 9000 20f3  .byte    0xe7, 0x88, 0x90, 0x00, 0x20, 0xf3
0x3ff80025b4a:  e7cc d000 20f3  .byte    0xe7, 0xcc, 0xd0, 0x00, 0x20, 0xf3
0x3ff80025b50:  e700 1000 2ef3  .byte    0xe7, 0x00, 0x10, 0x00, 0x2e, 0xf3
0x3ff80025b56:  e744 5000 2ef3  .byte    0xe7, 0x44, 0x50, 0x00, 0x2e, 0xf3
0x3ff80025b5c:  e733 0000 006d  .byte    0xe7, 0x33, 0x00, 0x00, 0x00, 0x6d
0x3ff80025b62:  e777 4000 006d  .byte    0xe7, 0x77, 0x40, 0x00, 0x00, 0x6d
0x3ff80025b68:  e7bb 8000 006d  .byte    0xe7, 0xbb, 0x80, 0x00, 0x00, 0x6d
0x3ff80025b6e:  e7ff c000 006d  .byte    0xe7, 0xff, 0xc0, 0x00, 0x00, 0x6d
0x3ff80025b74:  e733 0000 0e6d  .byte    0xe7, 0x33, 0x00, 0x00, 0x0e, 0x6d
0x3ff80025b7a:  e777 4000 0e6d  .byte    0xe7, 0x77, 0x40, 0x00, 0x0e, 0x6d
0x3ff80025b80:  e733 0010 2033  .byte    0xe7, 0x33, 0x00, 0x10, 0x20, 0x33
0x3ff80025b86:  e777 0010 2033  .byte    0xe7, 0x77, 0x00, 0x10, 0x20, 0x33
0x3ff80025b8c:  e7bb 0010 2033  .byte    0xe7, 0xbb, 0x00, 0x10, 0x20, 0x33
0x3ff80025b92:  e7ff 0010 2033  .byte    0xe7, 0xff, 0x00, 0x10, 0x20, 0x33
0x3ff80025b98:  e733 0010 2c33  .byte    0xe7, 0x33, 0x00, 0x10, 0x2c, 0x33
0x3ff80025b9e:  e777 0010 2c33  .byte    0xe7, 0x77, 0x00, 0x10, 0x2c, 0x33
0x3ff80025ba4:  e722 3000 20f3  .byte    0xe7, 0x22, 0x30, 0x00, 0x20, 0xf3
0x3ff80025baa:  e766 7000 20f3  .byte    0xe7, 0x66, 0x70, 0x00, 0x20, 0xf3
0x3ff80025bb0:  e7aa b000 20f3  .byte    0xe7, 0xaa, 0xb0, 0x00, 0x20, 0xf3
0x3ff80025bb6:  e7ee f000 20f3  .byte    0xe7, 0xee, 0xf0, 0x00, 0x20, 0xf3
0x3ff80025bbc:  e722 3000 2ef3  .byte    0xe7, 0x22, 0x30, 0x00, 0x2e, 0xf3
0x3ff80025bc2:  e766 7000 2ef3  .byte    0xe7, 0x66, 0x70, 0x00, 0x2e, 0xf3
0x3ff80025bc8:  e711 2000 006d  .byte    0xe7, 0x11, 0x20, 0x00, 0x00, 0x6d
0x3ff80025bce:  e755 6000 006d  .byte    0xe7, 0x55, 0x60, 0x00, 0x00, 0x6d
0x3ff80025bd4:  e799 a000 006d  .byte    0xe7, 0x99, 0xa0, 0x00, 0x00, 0x6d
0x3ff80025bda:  e7dd e000 006d  .byte    0xe7, 0xdd, 0xe0, 0x00, 0x00, 0x6d
0x3ff80025be0:  e711 2000 0e6d  .byte    0xe7, 0x11, 0x20, 0x00, 0x0e, 0x6d
0x3ff80025be6:  e755 6000 0e6d  .byte    0xe7, 0x55, 0x60, 0x00, 0x0e, 0x6d
0x3ff80025bec:  e711 000c 2033  .byte    0xe7, 0x11, 0x00, 0x0c, 0x20, 0x33
0x3ff80025bf2:  e755 000c 2033  .byte    0xe7, 0x55, 0x00, 0x0c, 0x20, 0x33
0x3ff80025bf8:  e799 000c 2033  .byte    0xe7, 0x99, 0x00, 0x0c, 0x20, 0x33
0x3ff80025bfe:  e7dd 000c 2033  .byte    0xe7, 0xdd, 0x00, 0x0c, 0x20, 0x33
0x3ff80025c04:  e711 000c 2c33  .byte    0xe7, 0x11, 0x00, 0x0c, 0x2c, 0x33
0x3ff80025c0a:  e755 000c 2c33  .byte    0xe7, 0x55, 0x00, 0x0c, 0x2c, 0x33
0x3ff80025c10:  e700 1000 20f3  .byte    0xe7, 0x00, 0x10, 0x00, 0x20, 0xf3
0x3ff80025c16:  e744 5000 20f3  .byte    0xe7, 0x44, 0x50, 0x00, 0x20, 0xf3
0x3ff80025c1c:  e788 9000 20f3  .byte    0xe7, 0x88, 0x90, 0x00, 0x20, 0xf3
0x3ff80025c22:  e7cc d000 20f3  .byte    0xe7, 0xcc, 0xd0, 0x00, 0x20, 0xf3
0x3ff80025c28:  e700 1000 2ef3  .byte    0xe7, 0x00, 0x10, 0x00, 0x2e, 0xf3
0x3ff80025c2e:  e744 5000 2ef3  .byte    0xe7, 0x44, 0x50, 0x00, 0x2e, 0xf3
0x3ff80025c34:  e733 0000 006d  .byte    0xe7, 0x33, 0x00, 0x00, 0x00, 0x6d
0x3ff80025c3a:  e777 4000 006d  .byte    0xe7, 0x77, 0x40, 0x00, 0x00, 0x6d
0x3ff80025c40:  e7bb 8000 006d  .byte    0xe7, 0xbb, 0x80, 0x00, 0x00, 0x6d
0x3ff80025c46:  e7ff c000 006d  .byte    0xe7, 0xff, 0xc0, 0x00, 0x00, 0x6d
0x3ff80025c4c:  e733 0000 0e6d  .byte    0xe7, 0x33, 0x00, 0x00, 0x0e, 0x6d
0x3ff80025c52:  e777 4000 0e6d  .byte    0xe7, 0x77, 0x40, 0x00, 0x0e, 0x6d
0x3ff80025c58:  e733 0008 2033  .byte    0xe7, 0x33, 0x00, 0x08, 0x20, 0x33

Regards,

Phil.
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