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

[Christian Hagedorn]

On Wed, 19 Oct 2022 12:11:30 GMT, Xiaolin Zheng <xlinzheng at openjdk.org> wrote:

>> 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

> > We could additionally assert that the real terminating entry is indeed `(0, 0)` as specified in the spec. But you need to check if that is the case on RISC-V.
> 
> Thanks for your time for reviewing! In fact, before submitting this PR I had one assertion to assert when the new `is_terminating_entry()` returns true, we must encounter a pair of zero. Though I removed it at last because I wanted to fully mirror what Binutils is doing. Of course, I think the assertion is reasonable and on RISC-V it is the same case that the real terminating entry is a pair of 0. So going to add that assertion back.

Yeah, I think so, too - thanks for adding it back!

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Marked as reviewed by chagedorn (Reviewer).

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