RFR: 8186780: clang-4.0 fastdebug assertion failure in os_linux_x86:os::verify_stack_alignment()

[Martin Buchholz]

Hi David and build-dev folk,

After way too much build/hotspot hacking, I have a better fix:

clang inlined os::current_stack_pointer into its caller __in the same
translation unit___ (that could be fixed in a separate change) so of course
in this case it didn't have to follow the ABI.  Fix is obvious in hindsight:

-address os::current_stack_pointer() {
+NOINLINE address os::current_stack_pointer() {

While working on this I noticed that the clang stack alignment flags on
Linux are missing.  They should be moved from a macosx-specific check to a
clang-specific check.  macosx is not synonymous with clang!

--- a/make/autoconf/flags-cflags.m4
+++ b/make/autoconf/flags-cflags.m4
@@ -470,6 +470,14 @@ AC_DEFUN([FLAGS_SETUP_CFLAGS_HELPER],
     # COMMON to gcc and clang
     TOOLCHAIN_CFLAGS_JVM="-pipe -fno-rtti -fno-exceptions \
         -fvisibility=hidden -fno-strict-aliasing -fno-omit-frame-pointer"
+
+    if test "x$TOOLCHAIN_TYPE" = xclang; then
+      # In principle the stack alignment below is cpu- and ABI-dependent
and
+      # should agree with values of StackAlignmentInBytes in various
+      # src/hotspot/cpu/*/globalDefinitions_*.hpp files, but this value
+      # currently works for all platforms.
+      TOOLCHAIN_CFLAGS_JVM="$TOOLCHAIN_CFLAGS_JVM
-mno-omit-leaf-frame-pointer -mstack-alignment=16"
+    fi
   fi

   if test "x$TOOLCHAIN_TYPE" = xgcc; then
@@ -601,10 +609,6 @@ AC_DEFUN([FLAGS_SETUP_CFLAGS_HELPER],
     fi
   fi

-  if test "x$OPENJDK_TARGET_OS" = xmacosx; then
-    OS_CFLAGS_JVM="$OS_CFLAGS_JVM -mno-omit-leaf-frame-pointer
-mstack-alignment=16"
-  fi
-
   # Optional POSIX functionality needed by the JVM
   #
   # Check if clock_gettime is available and in which library. This
indicates


8186780: clang-4.0 fastdebug assertion failure in
os_linux_x86:os::verify_stack_alignment()
http://cr.openjdk.java.net/~martin/webrevs/jdk/clang-stack-alignment/
https://bugs.openjdk.java.net/browse/JDK-8186780

On Wed, Jun 20, 2018 at 12:30 AM, David Holmes <david.holmes at oracle.com>
wrote:

> Hi Martin,
>
>
> On 20/06/2018 3:03 AM, Martin Buchholz wrote:
>
>> (There's surely a better fix that involves refactoring os/cpu/compiler
>> support)
>>
>> 8186780: clang-4.0 fastdebug assertion failure in
>> os_linux_x86:os::verify_stack_alignment()
>> http://cr.openjdk.java.net/~martin/webrevs/jdk/clang-verify_
>> stack_alignment/
>> https://bugs.openjdk.java.net/browse/JDK-8186780
>>
>
> I remain concerned about what it may mean for the stack pointer to not be
> aligned. I would have thought stack pointer alignment was part of the ABI
> for a CPU architecture, not something the compiler could choose at will?
> What about all the other code that uses StackAlignmentInBytes ??
>
> That aside your fix excludes the assert when building with clang for linux
> x86 as intended. And I see that for BSD x86 (where we also use clang) that
> verify_stack_alignment is empty.
>
> Thanks,
> David
>