[Qemu-devel] [Bug 1605123] [NEW] PEXT returns wrong values, seemingly switches arguments

[Lenard Szolnoki]

Public bug reported:

Hi,

I fiddled with BMI2 instructions and discovered that pext instructions
emulated with "qemu-x86_64 -cpu Haswell" return the wrong value. It
seemingly switches up its arguments. I suspect that the error is around the
gen_helper_pext(...) call in target-i386/translate.c. I checked helper_pext
in target-i386/int_helper.c and it works fine.

I ran my program on a CPU with BMI2 instruction set too, and it indeed
returns different values.

I didn't check pdep, it could have the same problem.

$ qemu-x86_64 --version
qemu-x86_64 version 2.6.50 (v2.6.0-2095-ge66b05e-dirty), Copyright (c) 
2003-2008 Fabrice Bellard

$ uname -a
Linux lenard-hp 4.3.0-1-amd64 #1 SMP Debian 4.3.5-1 (2016-02-06) x86_64 
GNU/Linux

I compiled the attached file with the command line "gcc -o main -g
-mbmi2 main.c".

$ gcc --version
gcc (Debian 5.4.0-6) 5.4.0 20160609

Best regards,
Lénárd Szolnoki

** Affects: qemu
     Importance: Undecided
         Status: New

** Attachment added: "main.c"
   https://bugs.launchpad.net/bugs/1605123/+attachment/4704470/+files/main.c

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https://bugs.launchpad.net/bugs/1605123

Title:
  PEXT returns wrong values, seemingly switches arguments

Status in QEMU:
  New

Bug description:
  Hi,

  I fiddled with BMI2 instructions and discovered that pext instructions
  emulated with "qemu-x86_64 -cpu Haswell" return the wrong value. It
  seemingly switches up its arguments. I suspect that the error is around the
  gen_helper_pext(...) call in target-i386/translate.c. I checked helper_pext
  in target-i386/int_helper.c and it works fine.

  I ran my program on a CPU with BMI2 instruction set too, and it indeed
  returns different values.

  I didn't check pdep, it could have the same problem.

  $ qemu-x86_64 --version
  qemu-x86_64 version 2.6.50 (v2.6.0-2095-ge66b05e-dirty), Copyright (c) 
2003-2008 Fabrice Bellard

  $ uname -a
  Linux lenard-hp 4.3.0-1-amd64 #1 SMP Debian 4.3.5-1 (2016-02-06) x86_64 
GNU/Linux

  I compiled the attached file with the command line "gcc -o main -g
  -mbmi2 main.c".

  $ gcc --version
  gcc (Debian 5.4.0-6) 5.4.0 20160609

  Best regards,
  Lénárd Szolnoki

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