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[Bug 1906536] Re: Unable to set SVE VL to 1024 bits or above since 7b6a2


From: Thomas Huth
Subject: [Bug 1906536] Re: Unable to set SVE VL to 1024 bits or above since 7b6a2198
Date: Wed, 14 Jul 2021 14:28:09 -0000

This is an automated cleanup. This bug report has been moved to QEMU's
new bug tracker on gitlab.com and thus gets marked as 'expired' now.
Please continue with the discussion here:

 https://gitlab.com/qemu-project/qemu/-/issues/482


** Changed in: qemu
       Status: New => Expired

** Bug watch added: gitlab.com/qemu-project/qemu/-/issues #482
   https://gitlab.com/qemu-project/qemu/-/issues/482

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https://bugs.launchpad.net/bugs/1906536

Title:
  Unable to set SVE VL to 1024 bits or above since 7b6a2198

Status in QEMU:
  Expired

Bug description:
  Prior to 7b6a2198e71794c851f39ac7a92d39692c786820, the QEMU option
  sve-max-vq could be used to set the vector length of the
  implementation. This is useful (among other reasons) for testing
  software compiled with a fixed SVE vector length. Since this commit,
  the vector length is capped at 512 bits.

  To reproduce the issue:

  $ cat rdvl.s
  .global _start
  _start:
    rdvl x0, #1
    asr x0, x0, #4
    mov x8, #93 // exit
    svc #0
  $ aarch64-linux-gnu-as -march=armv8.2-a+sve rdvl.s -o rdvl.o
  $ aarch64-linux-gnu-ld rdvl.o
  $ for vl in 1 2 4 8 16; do ../build-qemu/aarch64-linux-user/qemu-aarch64 -cpu 
max,sve-max-vq=$vl a.out; echo $?; done
  1
  2
  4
  4
  4

  For a QEMU built prior to the above revision, we get the output:
  1
  2
  4
  8
  16

  as expected. It seems that either the old behavior should be restored,
  or there should be an option to force a higher vector length?

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