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  1. JDK
  2. JDK-8214465

Upgrade arm-sflt minimum architecture to ARMv5TE for assembler



    • b23
    • arm


      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 linux_arm_32.s uses PLD
      > instructions. ARM ISA manual mentions this: "This instruction is
      > available in E variants of ARM architecture v5 and above."

      Follow up:

      > "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 <hardware> does support ldrd/strd but they do not support 4 byte
      > aligned operations. The addresses must be 8 byte aligned."

      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

      # HG changeset patch
      # User Jakub Vaněk <linuxtardis@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])
      + # --- 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$OPENJDK_TARGET_ABI_PROFILE" = xarm-vfp-sflt; then
             ARM_ARCH_TYPE_FLAGS='-march=armv7-a -mthumb'
      @@ -57,11 +62,11 @@
           elif test "x$OPENJDK_TARGET_ABI_PROFILE" = xarm-sflt; then
             ARM_ARCH_TYPE_FLAGS='-march=armv5t -marm'
      - ARM_ARCH_TYPE_ASFLAGS='-march=armv5t'
      + ARM_ARCH_TYPE_ASFLAGS='-march=armv5te'
           elif test "x$OPENJDK_TARGET_ABI_PROFILE" = xarmv5-vfp-sflt; then
             ARM_ARCH_TYPE_FLAGS='-march=armv5t -marm'
      - ARM_ARCH_TYPE_ASFLAGS='-march=armv5t'
      + ARM_ARCH_TYPE_ASFLAGS='-march=armv5te'
           elif test "x$OPENJDK_TARGET_ABI_PROFILE" = xarmv6-vfp-hflt; then
             ARM_ARCH_TYPE_FLAGS='-march=armv6 -marm'


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              dholmes David Holmes
              dholmes David Holmes
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