8358696: Assert with extreme values for -XX:BciProfileWidth

[sarannat]

Issue
Extreme values for BciProfileWidth flag such as java -XX:BciProfileWidth=-1 -version and java -XX:BciProfileWidth=100000 -version results in assert failure assert(allocates2(pc)) failed: not in CodeBuffer memory: 0x0000772b63a7a3a0 <= 0x0000772b63b75159 <= 0x0000772b63b75158 . This is observed in a x86 machine.

Analysis
On debugging the issue, I found that increasing the size of the interpreter using the InterpreterCodeSize variable in src/hotspot/cpu/x86/templateInterpreterGenerator_x86.cpp prevented the above mentioned assert from failing for large values of BciProfileWidth.

Proposal
Considering the fact that larger BciProfileWidth results in slower profiling, I have proposed a range between 0 to 5000 to restrict the value for BciProfileWidth for x86 machines. This maximum value is based on modifying the InterpreterCodeSize variable in src/hotspot/cpu/x86/templateInterpreterGenerator_x86.cpp using the smallest InterpreterCodeSize for all the architectures. As for the lower bound, a value of -1 would be the same as 0, as this simply means no return bci's will be recorded in ret profile.

Issue in AArch64
Additionally running the command java -XX:BciProfileWidth= 10000 -version (or larger values) results in a different failure assert(offset_ok_for_immed(offset(), size)) failed: must be, was: 32768, 3 on an AArch64 machine.This is an issue of maximum offset for ldr/str in AArch64 which can be fixed using form_address as mentioned in JDK-8342736. In my preliminary fix using form_address on AArch64 machine. I had to modify 3 ldr and 1 str instruction (in file src/hotspot/cpu/aarch64/interp_masm_aarch64.cpp at line number 926, 983, and 997). With this fix using form_address, BciProfileWidth works for maximum of 5000 after which it crashes withassert(allocates2(pc)) failed: not in CodeBuffer memory: 0x0000772b63a7a3a0 <= 0x0000772b63b75159 <= 0x0000772b63b75158 . Without this fix BciProfileWidth works for a maximum value of 1300. Currently, I have suggested to restrict the upper bound on AArch64 to 1000 instead of fixing it with form_address.

Question to reviewers
Do you think this is a reasonable fix ? For AArch64 do you suggest fixing using form_address ? If yes, do I fix it under this PR or create another one ?

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Issue

• JDK-8358696: Assert with extreme values for -XX:BciProfileWidth (Bug - P4)

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[bridgekeeper]

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