[PATCH v2] Upgrade arm-sflt minimum architecture to ARMv5TE (original) (raw)

Jakub Vaněk linuxtardis at gmail.com
Wed Nov 28 21:17:22 UTC 2018

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Hi David,

On 2018-11-26 at 17:36 +1000, David Holmes wrote:

Hi Jakub,

On 26/11/2018 1:53 am, Jakub Vaněk wrote: > Hi, > > This patch raises the minimum architectural level for ARM CPUs to > ARMv5TE. It is done through changing the -march flag in the current > CPU-specific CFLAGS and ASFLAGS. > > This patch depends on "Append assembler flags on ARM targets" patch > for > ASFLAGS handling. > > Reason for this change: assembler code in linuxarm32.s uses PLD > instructions. ARM ISA manual mentions this: "This instruction is > available in E variants of ARM architecture v5 and above." (thanks > to > David Holmes for noticing this). FYI I did a bit of digging and we tried to make this change back in 2010 and ran into problems: "It appears that gcc assumes that if you choose the armv5te architecture option, it can use the "E" instruction extensions which provide 64 bit load and stores to 4 byte aligned addresses. I tried two different compiler versions 4.1.2 and 4.2.3 and they both had the same problem. The does support ldrd/strd but they do not support 4 byte aligned operations. The addresses must be 8 byte aligned."

How things stand today I can not say.

I have searched for this and indeed, this bug wasn't fixed until recently: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82445

For our own use, it seems that Ubuntu gcc7 is patched, whether Debian gcc6 isn't. I think that the best solution is to keep armv5t in CFLAGS and only raise armv5te in ASFLAGS, where it is actually needed. This way GCC still generates older non-buggy code and the assembler works with pld. I have tested this configuration and it compiles successfully.

https://ci.adoptopenjdk.net/view/ev3dev/job/openjdk12_build_ev3_linux/40/

Thanks,

Jakub

Cheers, David

HG changeset patch

User Jakub Vaněk <linuxtardis at gmail.com>

Date 1543252130 -3600

Mon Nov 26 18:08:50 2018 +0100

Node ID bfd9e7032cfdc8c814ddaf4bb471a014fbbf1a89

Parent d2db3b32d5614029f2b1af2731c0d9ec10d88767

Fix undefined pld instruction on arm-sflt

diff --git a/make/autoconf/flags.m4 b/make/autoconf/flags.m4 --- a/make/autoconf/flags.m4 +++ b/make/autoconf/flags.m4 @@ -46,6 +46,11 @@ AC_MSG_CHECKING([for ABI profle]) AC_MSG_RESULT([$OPENJDK_TARGET_ABI_PROFILE])

• --- Arm-sflt CFLAGS and ASFLAGS ---

• Armv5te is required for assembler, because pld insn used in arm32 hotspot is only in v5E and above.

• However, there is also a GCC bug which generates unaligned strd/ldrd instructions on armv5te:

• https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82445, and it was fixed only quite recently.

• The resulting compromise is to enable v5TE for assembler and let GCC generate code for v5T.

  if test "x$OPENJDK_TARGET_ABI_PROFILE" = xarm-vfp-sflt; then ARM_FLOAT_TYPE=vfp-sflt ARM_ARCH_TYPE_FLAGS='-march=armv7-a -mthumb' @@ -57,11 +62,11 @@ elif test "x$OPENJDK_TARGET_ABI_PROFILE" = xarm-sflt; then ARM_FLOAT_TYPE=sflt ARM_ARCH_TYPE_FLAGS='-march=armv5t -marm'

•  ARM_ARCH_TYPE_ASFLAGS='-march=armv5t'

•  ARM_ARCH_TYPE_ASFLAGS='-march=armv5te'

  elif test "x$OPENJDK_TARGET_ABI_PROFILE" = xarmv5-vfp-sflt; then ARM_FLOAT_TYPE=vfp-sflt ARM_ARCH_TYPE_FLAGS='-march=armv5t -marm'

•  ARM_ARCH_TYPE_ASFLAGS='-march=armv5t'

•  ARM_ARCH_TYPE_ASFLAGS='-march=armv5te'

  elif test "x$OPENJDK_TARGET_ABI_PROFILE" = xarmv6-vfp-hflt; then ARM_FLOAT_TYPE=vfp-hflt ARM_ARCH_TYPE_FLAGS='-march=armv6 -marm'

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