aarch64 SVE emulation breaks strnlen and strrchr

[Szabolcs Nagy]

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

[Richard Henderson (rth)]

I don't know why the test worked previously, and I did not
investigate, but as far as I can tell, the test is broken.

The test is returning a value >= maxlen because it it using
the wrong increment. Fixed thus.

[Richard Henderson (rth)]

FWIW, as I think on this further, this probably isn't the
ideal fix -- I recall now that INCP is a "reduction" class
instruction and thus its overhead is non-trivial.

We could instead add an integer min operation at label 9,
which is outside of the main loop.

[Richard Henderson (rth)]

Bah. The code at label 9 does not match the comment.
Best fixed thus.

[Richard Henderson (rth)]

... 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).

[Richard Henderson (rth)]

Patch fixing strrchr:
https://<email address hidden>/

[Thomas Huth (th-huth)]

https://gitlab.com/qemu-project/qemu/-/commit/70acaafef2e053a3