RFR JDK-8194084: Obsolete FastTLABRefill and remove the related code

[Stuart Monteith]

Hi,
   I've tried with:

__ stp(r19, zr, Address(__ pre(sp, -wordSize*2)));

and

 __ ldp(r19, zr, Address(__ post(sp, wordSize*2)));

To save and restore r19.  We now get:

#
# A fatal error has been detected by the Java Runtime Environment:
#
#  SIGSEGV (0xb) at pc=0x0000010008e1ce5c, pid=15063, tid=15091
#
# JRE version: OpenJDK Runtime Environment (11.0) (fastdebug build
11-internal+0-adhoc.stuart.hs)
# Java VM: OpenJDK 64-Bit Server VM (fastdebug
11-internal+0-adhoc.stuart.hs, mixed mode, tiered, compressed oops,
serial gc, linux-aarch64)
# Problematic frame:
# J 473 c1 java.io.BufferedReader.readLine(Z)Ljava/lang/String;
java.base (304 bytes) @ 0x0000010008e1ce5c
[0x0000010008e1cb40+0x000000000000031c]
#
siginfo: si_signo: 11 (SIGSEGV), si_code: 1 (SEGV_MAPERR), si_addr:
0x000000000000002c

java/io/BufferedReader.readLine(Z)Ljava/lang/String;
[0x0000010008e1cb40, 0x0000010008e1d9c0]  3712 bytes
[Entry Point]
[Constants]
  # {method} {0x00000100025663b0} 'readLine' '(Z)Ljava/lang/String;'
in 'java/io/BufferedReader'
  # this:     c_rarg1:c_rarg1
                        = 'java/io/BufferedReader'
  # parm0:    c_rarg2   = boolean
  #           [sp+0x120]  (sp of caller)
 ;;  block B45 [0, 0]

  0x0000010008e1cb40: ldr       w8, [x1,#8]
  0x0000010008e1cb44: cmp       x9, x8, lsl #3
  0x0000010008e1cb48: b.eq      0x0000010008e1cb80
  0x0000010008e1cb4c: adrp      x8, 0x00000100080a5000
[error occurred during error reporting (printing code blob if possible), id 0xb]


It looks like more is wrong here than just the saving/restoration of
r19. I'll review the changes a bit more closely.

BR,
   Stuart


On 19 February 2018 at 15:15, Andrew Dinn <adinn at redhat.com> wrote:
> On 19/02/18 14:24, Stuart Monteith wrote:
>> I've tried building with Aleksey's patch
>> (http://cr.openjdk.java.net/~shade/8198341/fixes.patch), but came
>> across a JVM crash when building OpenJDK.
>>
>> I need to look a bit closer, but the patch "8194084: Obsolete
>> FastTLABRefill and remove the related code" is causing SIGBUS
>> BUS_ADRALN errors. The stack pointer is becoming unaligned, and so
>> breaks on aarch64.
>> For example, in your patch you do:
>>
>> -          __ ldp(r5, r19, Address(__ post(sp, 2 * wordSize)));
>> +          __ ldr(r19, Address(__ post(sp, wordSize)));
>>
>> You can only have a 16-byte aligned stack pointer, and you replaced
>> two loads with one, resulting in an unaligned SP.
> Yes, I believe Stuart has diagnosed this correctly. The problem is in
> the changes in c1_Runtime1_aarch64.cpp. The original stp with
> pre-decrement instruction that save r19+r5 retained 16-byte alignment
> for rsp. The replacement single str with pre-decrement instruction
> misaligns sp -- and AArch64 hw gets /very/ unhappy when that happens.
>
> Three may be no need to save and restore r5, per se, but there is still
> a need to push and restore 16 byte's worth of stack data. The str and
> ldr instructions which currently save/restore r19 could simply be
> reverted to stp and ldp of r5+r19 (it does no harm to save/restore r5).
> However, it would be better to save and restore zr+r19. That would
> better indicate the uselessness of the zr stack slot.
>
> regards,
>
>
> Andrew Dinn
> -----------
>