[Bug 1908551] Re: aarch64 SVE emulation breaks strnlen and strrchr

[Richard Henderson]

... but you also mentioned strrchr, and there is a qemu bug there.  The
REV (predicate) instruction doesn't seem to be doing the right thing --
input 0x1 -> output 0x80000000 which is not correct for the current
vector length (64).

** Changed in: qemu
       Status: Invalid => Confirmed

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Title:
  aarch64 SVE emulation breaks strnlen and strrchr

Status in QEMU:
  Confirmed

Bug description:
  arm optimized-routines have sve string functions with test code.

  the test worked up until recently: with qemu-5.2.0 i see

  $ qemu-aarch64 build/bin/test/strnlen
  PASS strnlen
  PASS __strnlen_aarch64
  __strnlen_aarch64_sve (0x490fa0, 32) len 32 returned 64, expected 32
  input: "abcdefghijklmnopqrstuvwxyz\{|}~\x7f\x80"
  __strnlen_aarch64_sve (0x490fa0, 32) len 33 returned 64, expected 32
  input: "abcdefghijklmnopqrstuvwxyz\{|}~\x7f\x80a"
  __strnlen_aarch64_sve (0x490fa0, 33) len 33 returned 64, expected 33
  input: "abcdefghijklmnopqrstuvwxyz\{|}~\x7f\x80a"
  __strnlen_aarch64_sve (0x490fa0, 32) len 34 returned 64, expected 32
  input: "abcdefghijklmnopqrstuvwxyz\{|}~\x7f\x80ab"
  __strnlen_aarch64_sve (0x490fa0, 33) len 34 returned 64, expected 33
  input: "abcdefghijklmnopqrstuvwxyz\{|}~\x7f\x80ab"
  __strnlen_aarch64_sve (0x490fa0, 34) len 34 returned 64, expected 34
  input: "abcdefghijklmnopqrstuvwxyz\{|}~\x7f\x80ab"
  __strnlen_aarch64_sve (0x490fa0, 32) len 35 returned 64, expected 32
  input: "abcdefghijklmnopqrstuvwxyz\{|}~\x7f\x80a\x00c"
  __strnlen_aarch64_sve (0x490fa0, 33) len 35 returned 64, expected 33
  input: "abcdefghijklmnopqrstuvwxyz\{|}~\x7f\x80ab\x00"
  __strnlen_aarch64_sve (0x490fa0, 34) len 35 returned 64, expected 34
  input: "abcdefghijklmnopqrstuvwxyz\{|}~\x7f\x80abc"
  __strnlen_aarch64_sve (0x490fa0, 35) len 35 returned 64, expected 35
  input: "abcdefghijklmnopqrstuvwxyz\{|}~\x7f\x80abc"
  FAIL __strnlen_aarch64_sve

  however the test passes with

  qemu-aarch64 -cpu max,sve-max-vq=2

  there should be nothing vector length specific in the code.

  i haven't debugged it further, to reproduce the issue clone
  https://github.com/ARM-software/optimized-routines

  and run 'make build/bin/test/strnlen' with a config.mk like

  SUBS = string
  ARCH = aarch64
  CROSS_COMPILE = aarch64-none-linux-gnu-
  CC = $(CROSS_COMPILE)gcc
  CFLAGS = -std=c99 -pipe -O3
  CFLAGS += -march=armv8.2-a+sve
  EMULATOR = qemu-aarch64

  (native compilation works too, and you can run 'make check' to
  run all string tests) this will build a static linked executable
  into build/bin/test. if you want a smaller test case edit
  string/test/strnlen.c

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