On Friday, January 31, 2020, Alex Bennée <alex.bennee@linaro.org> wrote:

> ** Tags added: tcg testcase
>
> --
> You received this bug notification because you are a member of qemu-
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> https://bugs.launchpad.net/bugs/1861404
>
> Title:
>   AVX instruction VMOVDQU implementation error for YMM registers
>
>
If I remember well, there is no support for AVX instructions in linux-user
mode.

If that is true, how come handling of unsupported instruction went that far?

Did you try other AVX instructions?

Aleksandar




> Status in QEMU:
>   New
>
> Bug description:
>   Hi,
>
>   Tested with Qemu 4.2.0, and with git version
>   bddff6f6787c916b0e9d63ef9e4d442114257739.
>
>   The x86 AVX instruction VMOVDQU doesn't work properly with YMM registers
> (32 bytes).
>   It works with XMM registers (16 bytes) though.
>
>   See the attached test case `ymm.c`: when copying from memory-to-ymm0
>   and then back from ymm0-to-memory using VMOVDQU, Qemu only copies the
>   first 16 of the total 32 bytes.
>
>   ```
>   user@ubuntu ~/Qemu % gcc -o ymm ymm.c -Wall -Wextra -Werror
>
>   user@ubuntu ~/Qemu % ./ymm
>   00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F 10 11 12 13 14 15 16 17
> 18 19 1A 1B 1C 1D 1E 1F
>
>   user@ubuntu ~/Qemu % ./x86_64-linux-user/qemu-x86_64 -cpu max ymm
>   00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F 00 00 00 00 00 00 00 00
> 00 00 00 00 00 00 00 00
>   ```
>
>   This seems to be because in `translate.c > gen_sse()`, the case
>   handling the VMOVDQU instruction calls `gen_ldo_env_A0` which always
>   performs a 16 bytes copy using two 8 bytes load and store operations
>   (with `tcg_gen_qemu_ld_i64` and `tcg_gen_st_i64`).
>
>   Instead, the `gen_ldo_env_A0` function should generate a copy with a
>   size corresponding to the used register.
>
>
>   ```
>   static void gen_sse(CPUX86State *env, DisasContext *s, int b,
>                       target_ulong pc_start, int rex_r)
>   {
>           [...]
>           case 0x26f: /* movdqu xmm, ea */
>               if (mod != 3) {
>                   gen_lea_modrm(env, s, modrm);
>                   gen_ldo_env_A0(s, offsetof(CPUX86State, xmm_regs[reg]));
>               } else {
>           [...]
>   ```
>
>   ```
>   static inline void gen_ldo_env_A0(DisasContext *s, int offset)
>   {
>       int mem_index = s->mem_index;
>       tcg_gen_qemu_ld_i64(s->tmp1_i64, s->A0, mem_index, MO_LEQ);
>       tcg_gen_st_i64(s->tmp1_i64, cpu_env, offset + offsetof(ZMMReg,
> ZMM_Q(0)));
>       tcg_gen_addi_tl(s->tmp0, s->A0, 8);
>       tcg_gen_qemu_ld_i64(s->tmp1_i64, s->tmp0, mem_index, MO_LEQ);
>       tcg_gen_st_i64(s->tmp1_i64, cpu_env, offset + offsetof(ZMMReg,
> ZMM_Q(1)));
>   }
>   ```
>
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>