[PATCH v2] Upgrade arm-sflt minimum architecture to ARMv5TE
linuxtardis at gmail.com
Wed Nov 28 21:17:22 UTC 2018
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 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." (thanks
> > to
> > David Holmes for noticing this).
> FYI I did a bit of digging and we tried to make this change back in
> and ran into problems:
> "It appears that gcc assumes that if you choose the armv5te
> option, it can use the "E" instruction extensions which provide 64
> 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
> The <hardware> 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
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 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
@@ -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$OPENJDK_TARGET_ABI_PROFILE" = xarm-vfp-sflt; then
@@ -57,11 +62,11 @@
elif test "x$OPENJDK_TARGET_ABI_PROFILE" = xarm-sflt; then
elif test "x$OPENJDK_TARGET_ABI_PROFILE" = xarmv5-vfp-sflt; then
elif test "x$OPENJDK_TARGET_ABI_PROFILE" = xarmv6-vfp-hflt; then
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