RFR: 8295646: Ignore zero pairs in address descriptors read by dwarf parser [v2]

[Xiaolin Zheng]

> RISC-V generates debuginfo like
> 
> 
>> readelf --debug-dump=aranges build/linux-riscv64-server-fastdebug/images/test/hotspot/gtest/server/libjvm.so
> 
> ... 
> Length:                   1756
>   Version:                  2
>   Offset into .debug_info:  0x4bc5e9
>   Pointer Size:             8
>   Segment Size:             0
> 
>     Address            Length
>     0000000000344ece 0000000000004a2c
>     0000000000000000 0000000000000000     <=
>     0000000000000000 0000000000000000     <=
>     0000000000000000 0000000000000000     <=
>     00000000003498fa 0000000000000016
>     0000000000349910 0000000000000016
>     ....
>     000000000026d5b8 0000000000000b9a
>     000000000034a532 0000000000000628
>     000000000034ab5a 00000000000002ac
>     0000000000000000 0000000000000000     <=
>     0000000000000000 0000000000000000
>     0000000000000000 0000000000000000
>     000000000034ae06 0000000000000bee
>     000000000034b9f4 0000000000000660
>     000000000034c054 00000000000005aa
>     0000000000000000 0000000000000000
>     0000000000000000 0000000000000000     <=
>     000000000034c5fe 0000000000000af2
>     000000000034d0f0 0000000000000f16
>     000000000034e006 0000000000000b4a
>     0000000000000000 0000000000000000
>     0000000000000000 0000000000000000
>     000000000026e152 000000000000000e
>     0000000000000000 0000000000000000
> 
> 
> Our dwarf parser (gdb's dwarf parser before this April is as well [1], which encountered the same issue on RISC-V) uses `address == 0 && size == 0` in `is_terminating_entry()` to detect terminations of an arange section, which will early terminate parsing RISC-V's debuginfo at an "apparent terminator" described in [1] so that the result would not look correct with tests failures. The `_header._unit_length` is read but not used and it is the real length that can determine the section's end, so we can use it to get the end position of a section instead of `address == 0 && size == 0` checks to fix this issue.
> 
> Also, the reason why `readelf` has no such issue is it also uses the same approach to determine the end position. [2]
> 
> Tests added along with the dwarf parser patch are all tested and passed on x86_64, aarch64, and riscv64.
> Running a tier1 sanity test now.
> 
> Thanks,
> Xiaolin
> 
> [1] https://github.com/bminor/binutils-gdb/commit/1a7c41d5ece7d0d1aa77d8019ee46f03181854fa
> [2] https://github.com/bminor/binutils-gdb/blob/fd320c4c29c9a1915d24a68a167a5fd6d2c27e60/binutils/dwarf.c#L7594

Xiaolin Zheng has updated the pull request incrementally with one additional commit since the last revision:

  Add the assertion back

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/10758/files
  - new: https://git.openjdk.org/jdk/pull/10758/files/c80408ed..76904650

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=10758&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=10758&range=00-01

  Stats: 9 lines in 2 files changed: 5 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/10758.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10758/head:pull/10758

PR: https://git.openjdk.org/jdk/pull/10758