libgcrypt clang asm configure issue.

[Dmytro Kovalov]

Hello,

I found a strange libgcrypt behavior on ARM with clang built.

There is a big gap in performance of libgcrypt, built by clang, in
comparison with gcc on my ARM target machine.
The simple profile test shows 100-500% advantage of gcc gcrypt.
I found an awkward workaround to beat this issue, but need your help to
find the best way to fix it.

The root cause is next:
Due to clang strict assembler syntax rules the unified assembler ARM check
doesn't pass.
Assembler check fails while ./configure for flags:
HAVE_COMPATIBLE_GCC_ARM_PLATFORM_AS
HAVE_GCC_INLINE_ASM_NEON

As a workaround I remove '%' from registers names in
configure.ac,
arm mips lib *.S files,
cipher/*arm.S,*armv7-neon.S files.

Could you please help with a more correct - polite way to compile libgcrypt
with assembler code?

Tested on:
libgcrypt-1.8.6
libgcrypt-1.9.3

Equipment:

build machine:
intel based cpu x86_64
Ubnuntu-20.04

Software
compiler        : clang 11.1.0
linker lld      : lld 11.1.0
assembler       : llvm-as 11.1.0
cflags          : "-m32 -march=armv7-a -mthumb -mfpu=vfpv3-d16
--target=arm-linux-gnueabihf"

arm-linux-gnueabihf sysroot based on glibc 2.31

libgcrypt configuring:
CC="arm-linux-gnueabihf-clang" \
./configure \
  --with-libgpg-error-prefix=<libgpg.so path> \
  --prefix=<output path> \
  --host=arm-linux-gnueabihf \
  --enable-static \
  --disable-doc


target machine:
hardware:
model name : ARMv7 Processor rev 4 (v7l)
BogoMIPS : 2304.00
Features : half thumb fastmult vfp edsp neon vfpv3 tls vfpv4 idiva idivt
vfpd32 lpae aes pmull sha1 sha2 crc32


Best Regards,
Dmytro Kovalov
Dmytro.a.kovalov at globallogic.com
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