RFR: 8367609: serviceability/sa/ClhsdbPmap.java fails when built with Clang [v2]

[Francesco Andreuzzi]

> The problem seems to be in read_lib_segments (ps_core.c), this check is too harsh:
> 
> https://github.com/openjdk/jdk/blob/5271448b3a013b2e3edcd619a4a3b975b292dae1/src/jdk.hotspot.agent/linux/native/libsaproc/ps_core.c#L423-L425
> 
> In my run, `existing_map->memsz = 0xe24000`, while the rhs in L425 is `0xe23000`. According to the NT_FILE entry, this segment of `libjvm.so` has file offset 0x67f000. It seems that the linker aligned it down according to the page size (0x1000). The offset of the same segment according to `readelf -l libjvm.so` is 0x67fc80. This additional offset should be added to `p_memsz` to obtain the 0xe24000, which we see in the core dump.
> 
> I added some files to the ticket for context.

Francesco Andreuzzi has updated the pull request incrementally with one additional commit since the last revision:

  simplify

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/27274/files
  - new: https://git.openjdk.org/jdk/pull/27274/files/0c050d35..795338e6

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=27274&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=27274&range=00-01

  Stats: 3 lines in 1 file changed: 0 ins; 1 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/27274.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27274/head:pull/27274

PR: https://git.openjdk.org/jdk/pull/27274