RFR: 8234930: Use MAP_JIT when allocating pages for code cache on macOS
David Holmes
david.holmes at oracle.com
Mon Aug 31 02:44:03 UTC 2020
Hi Anton,
cc'ing hotspot-gc-dev as a number of GC files are touched, even though
in a trivial way. It also broadens the scope for people who understand
the detailed nuances of these mapping flags.
Cheers,
David
On 28/08/2020 11:57 pm, Anton Kozlov wrote:
> Hi,
>
> Could you please review a change for
>
> JDK-8234930: Use MAP_JIT when allocating pages for code cache on macOS
> Bug: https://bugs.openjdk.java.net/browse/JDK-8234930
> Webrev: http://cr.openjdk.java.net/~akozlov/8234930/webrev.00/
>
> 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.
>
> Thanks,
> Anton
>
> [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>
>
>
>
>
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