RFR: 8234930: Use MAP_JIT when allocating pages for code cache on macOS [v8]

[Anton Kozlov]

> Please review an updated RFR from https://mail.openjdk.java.net/pipermail/hotspot-runtime-dev/2020-August/041463.html
> 
> On macOS, MAP_JIT cannot be used with MAP_FIXED[1]. So pd_reserve_memory have to provide MAP_JIT for mmap(NULL, PROT_NONE), the function was made aware of exec permissions.
> 
> For executable and data regions, pd_commit_memory only unlocks the memory with mprotect, this should make no difference compared with old code.
> 
> For data regions, pd_uncommit_memory still uses a new overlapping anonymous mmap which returns pages to the OS and immediately reflects this in diagnostic tools like ps.  For executable regions it would require MAP_FIXED|MAP_JIT, so instead madvise(MADV_FREE)+mprotect(PROT_NONE) are used. They should also allow OS to reclaim pages, but apparently this does not happen immediately. In practice, it should not be a problem for executable regions, as codecache does not shrink (if I haven't missed anything, by the implementation and in principle).
> 
> Tested: 
> * local tier1
> * jdk-submit
> * codesign[2] with hardened runtime and allow-jit but without 
> allow-unsigned-executable-memory entitlements[3] produce a working bundle.
> 
> (adding GC group as suggested by @dholmes-ora)
> 
> 
> [1] https://github.com/apple/darwin-xnu/blob/master/bsd/kern/kern_mman.c#L227
> [2]
>  
>   codesign \
>     --sign - \
>     --options runtime \
>     --entitlements ents.plist \
>     --timestamp \
>     $J/bin/* $J/lib/server/*.dylib $J/lib/*.dylib
> [3]
>   <?xml version="1.0" encoding="UTF-8"?>
>   <!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
>   <plist version="1.0">
>     <dict>
>       <key>com.apple.security.cs.allow-jit</key>
>       <true/>
>       <key>com.apple.security.cs.disable-library-validation</key>
>       <true/>
>       <key>com.apple.security.cs.allow-dyld-environment-variables</key>
>       <true/>
>     </dict>
>   </plist>

Anton Kozlov has updated the pull request incrementally with one additional commit since the last revision:

  Update style

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/294/files
  - new: https://git.openjdk.java.net/jdk/pull/294/files/b3eb5b01..31fe1fb0

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=294&range=07
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=294&range=06-07

  Stats: 19 lines in 8 files changed: 0 ins; 0 del; 19 mod
  Patch: https://git.openjdk.java.net/jdk/pull/294.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/294/head:pull/294

PR: https://git.openjdk.java.net/jdk/pull/294