RFR: JDK-8143584 Aarch64: Load constant pool tag and class status with load acquire (original) (raw)

Hui Shi hui.shi at linaro.org
Tue Nov 24 13:23:33 UTC 2015

Hi,

Could someone help review and sponsor more runtime fix for aarch64? bug: https://bugs.openjdk.java.net/browse/JDK-8143584 webrev: http://cr.openjdk.java.net/~hshi/8143584/webrev/

This also fix some random crash in template interpreter. One of the crash test is langtools/test/tools/javac/TestLambdaToMethodStats.java. The symptom is: in checkcast, klass being checked is not valid klass pointer and trigger segmentation fault. The root cause is on aarch64 it miss load acquire when trying to read tag in constant pool before load resolved klass. Resolved class load might finish before tag load.

Code for checkcast before fix 0x7f8409a5a0: add x8, x3, #0x4 0x7f8409a5a4: ldrb w1, [x8,x19] // load tag 0x7f8409a5a8: cmp x1, #0x7 __ cmp(r1, JVM_CONSTANT_Class);

0x7f8409a62c: mov x3, x0 0x7f8409a630: add x0, x2, x19, uxtx #3 0x7f8409a634: ldr x0, [x0,#80] 0x7f8409a638: ldr w19, [x3,#8] // load resolved class 0x7f8409a63c: eor x19, x19, #0x800000000 // x19 hold klass being checked

Load resolved class might finish before load tag and read incorrect value. Fix is using load acquire when load tag. These tags are updated with release store in ConstantPool::release_tag_at_put (which uses OrderAccess::release_store), tags need be loaded with load acquire instruction ensure later resolved class load get correct klass. Fix is using load acquire when load tag and compare.

After fix: 0x0000007f8009a6a4: add x8, x8, x19 0x0000007f8009a6a8: ldarb w1, [x8] 0x0000007f8009a6ac: cmp x1, #0x7 0x0000007f8009a6b0: b.eq 0x0000007f8009a730 ….

0x0000007f8009a730: mov x3, x0 0x0000007f8009a734: add x0, x2, x19, uxtx #3 0x0000007f8009a738: ldr x0, [x0,#80] 0x0000007f8009a73c: ldr w19, [x3,#8] 0x0000007f8009a740: eor x19, x19, #0x800000000

Checking similar places for aarch64 runtime, more places needs similar fix:

  1. Instanceof is similar with checkcast
  2. "ldc", similar with load resolved class in checkcast, need load acquire when loading tag in constant pool
  3. "new" loads tag for resolved class.
  4. "new" Loads and checks class initialized status, class init status update is guarded with orderaccess::storestore, need guarantee order between load class initialize status and load "instance_size in InstanceKlass".
  5. C1 runtime checks if class initialize status when generate code for fast_new_instance_init_check_id, similar with "new".

Regards Shi Hui

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