8324123: aarch64: fix prfm literal encoding in assembler #17482

sandlerwang · 2024-01-18T10:02:59Z

Current prfm literal mode encoding in aarch64 assembler is not correct.
The prfm_literal instruction requires 31 and 30 bits to be 0x11, while current assembler encodes the two bits to be 0x11, which is a ldr instruction, not prfm.
For example, if adding the following code in stubGenerator
__ prfm(Address(__ pc()))
we get a ldr instruction like
ldr x0, 0x0000ffff83f8539c
but it should be a prfm instruction like
prfm pldl1keep, 0x0000ffff8ff8539c

The bug is caused in ld_st2, literal mode, bit 31 and 30 bits are set to (size & 0b01), while for prfm instructions, 31 and 30 bits must be 0b11.
void ld_st2(Register Rt, const Address &adr, int size, int op, int V = 0) {
starti;

f(V, 26); // general reg?
zrf(Rt, 0);

// Encoding for literal loads is done here (rather than pushed
// down into Address::encode) because the encoding of this
// instruction is too different from all of the other forms to
// make it worth sharing.
if (adr.getMode() == Address::literal) {
  assert(size == 0b10 || size == 0b11, "bad operand size in ldr");
  assert(op == 0b01, "literal form can only be used with loads");
  f(**size & 0b01, 31, 30**), f(0b011, 29, 27), f(0b00, 25, 24);
  int64_t offset = (adr.target() - pc()) >> 2;
  sf(offset, 23, 5);
  code_section()->relocate(pc(), adr.rspec());
  return;
}

f(size, 31, 30);
f(op, 23, 22); // str
adr.encode(&current_insn);

}

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Issue

JDK-8324123: aarch64: fix prfm literal encoding in assembler (Bug - P4)

Reviewers

Andrew Haley (@theRealAph - Reviewer) ⚠️ Review applies to 11d46ff7
Dean Long (@dean-long - Reviewer)

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bridgekeeper · 2024-01-18T10:04:07Z

👋 Welcome back wzhuo! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

openjdk · 2024-01-18T10:06:10Z

@sandlerwang The following label will be automatically applied to this pull request:

hotspot-compiler

When this pull request is ready to be reviewed, an "RFR" email will be sent to the corresponding mailing list. If you would like to change these labels, use the /label pull request command.

mlbridge · 2024-01-18T10:09:22Z

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theRealAph · 2024-01-19T08:55:42Z

src/hotspot/cpu/aarch64/assembler_aarch64.hpp

+      f(pfop, 4, 0);                                            \
+      int64_t offset = (adr.target() - pc()) >> 2;              \
+      sf(offset, 23, 5);                                        \
+    } else {                                                    \


This looks reasonable, but we don't need it to be inline. See the examples of adr and _adrp.

Thank you APH. I have updated the patch to make prfm no inline. Please check the commit
do not use inline for prfm encoding function

theRealAph

Thanks.

theRealAph · 2024-01-22T10:25:38Z

src/hotspot/cpu/aarch64/assembler_aarch64.cpp

@@ -187,6 +187,18 @@ void Address::lea(MacroAssembler *as, Register r) const {
    zrf(Rd, 0);
  }

+void Assembler::prfm(const Address &adr, prfop pfop) {


Suggested change

void Assembler::prfm(const Address &adr, prfop pfop) {

// This encoding is similar (but not quite identical) to the encoding used

// by literal ld/st. see JDK-8324123.

void Assembler::prfm(const Address &adr, prfop pfop) {

Thanks for your suggestions. I have added the comments, please check

theRealAph · 2024-01-23T09:49:47Z

src/hotspot/cpu/aarch64/assembler_aarch64.hpp

-
-  INSN(prfm, 0b11, 0b10); // FIXME: PRFM should not be used with
-                          // writeback modes, but the assembler
-                          // doesn't enfore that.


Don't we still need this comment?

Got the comments back.

theRealAph · 2024-01-23T11:53:50Z

src/hotspot/cpu/aarch64/assembler_aarch64.cpp

+// This encoding is similar (but not quite identical) to the encoding used
+// by literal ld/st. see JDK-8324123.
+// FIXME: PRFM should not be used with writeback modes, but the assembler
+// doesn't enfore that.


Suggested change

// doesn't enfore that.

// doesn't enforce that.

theRealAph

Good.

openjdk · 2024-01-23T11:56:05Z

@sandlerwang This change now passes all automated pre-integration checks.

ℹ️ This project also has non-automated pre-integration requirements. Please see the file CONTRIBUTING.md for details.

After integration, the commit message for the final commit will be:

8324123: aarch64: fix prfm literal encoding in assembler

Reviewed-by: aph, dlong

You can use pull request commands such as /summary, /contributor and /issue to adjust it as needed.

At the time when this comment was updated there had been 85 new commits pushed to the master branch:

b5995a7: 8302019: Clarify Elements.overrides
95310ea: 8223696: java/net/httpclient/MaxStreams.java failed with didn't finish within the time-out
39b756a: 8324492: Remove Atomic support for OopHandle
12b89cd: 8323717: Introduce test keyword for tests that need external dependencies
746a086: 8306767: Concurrent repacking of extra data in MethodData is potentially unsafe
ffe3bb6: 8324657: Intermittent OOME on exception message create
e709842: 8324636: Serial: Remove Generation::block_is_obj
7a798d3: 8324598: use mem_unit when working with sysinfo memory and swap related information
6d36eb7: 8322768: Optimize non-subword vector compress and expand APIs for AVX2 target.
9d1a6d1: 8323645: Remove unused internal sun.net.www.protocol.jar.URLJarFileCallBack interface
... and 75 more: https://git.openjdk.org/jdk/compare/ff8cc268fdaaf85299c94088a226b73e7eaf6bdb...master

As there are no conflicts, your changes will automatically be rebased on top of these commits when integrating. If you prefer to avoid this automatic rebasing, please check the documentation for the /integrate command for further details.

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➡️ To flag this PR as ready for integration with the above commit message, type /integrate in a new comment. (Afterwards, your sponsor types /sponsor in a new comment to perform the integration).

eme64 · 2024-01-23T17:11:32Z

@sandlerwang could there be a regression test for this bug?

sandlerwang · 2024-01-24T02:02:40Z

@sandlerwang could there be a regression test for this bug?

Sorry, I tried but cannot get a test for this bug, because the prfm literal encoding is not used in current tip.
I met the bug when I tried to use prfm to prefetch instructions, but no similar case in tip

eme64 · 2024-01-24T08:42:34Z

src/hotspot/cpu/aarch64/assembler_aarch64.cpp

@@ -187,6 +187,22 @@ void Address::lea(MacroAssembler *as, Register r) const {
    zrf(Rd, 0);
  }

+// This encoding is similar (but not quite identical) to the encoding used
+// by literal ld/st. see JDK-8324123.
+// FIXME: PRFM should not be used with writeback modes, but the assembler


FIXME: is it ok to leave this in the code?
I think we prefer filed RFE's to comments in the code that nobody will ever look at again.
You can put the RFE number in the code though.

Thanks. The FIXME was there because PRFM did not support pre/post indexing and we had no check for that.
Some guarantee checks were added and FIXME was removed.
Please check the last 3 patches.

Thanks @sandlerwang !

src/hotspot/cpu/aarch64/assembler_aarch64.cpp

theRealAph

Still good.

Co-authored-by: Andrew Haley <aph-open@littlepinkcloud.com>

sandlerwang · 2024-01-26T02:28:57Z

/integrate

openjdk · 2024-01-26T02:29:36Z

@sandlerwang
Your change (at version 62cce40) is now ready to be sponsored by a Committer.

D-D-H · 2024-01-26T02:29:55Z

/sponsor

openjdk · 2024-01-26T02:30:50Z

Going to push as commit bde8789.
Since your change was applied there have been 85 commits pushed to the master branch:

b5995a7: 8302019: Clarify Elements.overrides
95310ea: 8223696: java/net/httpclient/MaxStreams.java failed with didn't finish within the time-out
39b756a: 8324492: Remove Atomic support for OopHandle
12b89cd: 8323717: Introduce test keyword for tests that need external dependencies
746a086: 8306767: Concurrent repacking of extra data in MethodData is potentially unsafe
ffe3bb6: 8324657: Intermittent OOME on exception message create
e709842: 8324636: Serial: Remove Generation::block_is_obj
7a798d3: 8324598: use mem_unit when working with sysinfo memory and swap related information
6d36eb7: 8322768: Optimize non-subword vector compress and expand APIs for AVX2 target.
9d1a6d1: 8323645: Remove unused internal sun.net.www.protocol.jar.URLJarFileCallBack interface
... and 75 more: https://git.openjdk.org/jdk/compare/ff8cc268fdaaf85299c94088a226b73e7eaf6bdb...master

Your commit was automatically rebased without conflicts.

openjdk · 2024-01-26T02:30:57Z

@D-D-H @sandlerwang Pushed as commit bde8789.

💡 You may see a message that your pull request was closed with unmerged commits. This can be safely ignored.

mmyxym · 2024-02-28T09:11:45Z

/backport jdk21u-dev

openjdk · 2024-02-28T09:14:09Z

@mmyxym the backport was successfully created on the branch backport-mmyxym-bde87895 in my personal fork of openjdk/jdk21u-dev. To create a pull request with this backport targeting openjdk/jdk21u-dev:master, just click the following link:

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The title of the pull request is automatically filled in correctly and below you find a suggestion for the pull request body:

Hi all,

This pull request contains a backport of commit bde87895 from the openjdk/jdk repository.

The commit being backported was authored by Wang Zhuo on 26 Jan 2024 and was reviewed by Andrew Haley and Dean Long.

Thanks!

If you need to update the source branch of the pull then run the following commands in a local clone of your personal fork of openjdk/jdk21u-dev:

$ git fetch https://github.com/openjdk-bots/jdk21u-dev.git backport-mmyxym-bde87895:backport-mmyxym-bde87895
$ git checkout backport-mmyxym-bde87895
# make changes
$ git add paths/to/changed/files
$ git commit --message 'Describe additional changes made'
$ git push https://github.com/openjdk-bots/jdk21u-dev.git backport-mmyxym-bde87895

mmyxym · 2024-02-29T04:56:43Z

/backport jdk17u-dev

openjdk · 2024-02-29T04:57:44Z

@mmyxym Could not automatically backport bde87895 to openjdk/jdk17u-dev due to conflicts in the following files:

src/hotspot/cpu/aarch64/assembler_aarch64.cpp
src/hotspot/cpu/aarch64/assembler_aarch64.hpp

Please fetch the appropriate branch/commit and manually resolve these conflicts by using the following commands in your personal fork of openjdk/jdk17u-dev. Note: these commands are just some suggestions and you can use other equivalent commands you know.

# Fetch the up-to-date version of the target branch
$ git fetch --no-tags https://git.openjdk.org/jdk17u-dev.git master:master

# Check out the target branch and create your own branch to backport
$ git checkout master
$ git checkout -b backport-mmyxym-bde87895

# Fetch the commit you want to backport
$ git fetch --no-tags https://git.openjdk.org/jdk.git bde87895c8b1b9df198e3883d24cd9ea840efc98

# Backport the commit
$ git cherry-pick --no-commit bde87895c8b1b9df198e3883d24cd9ea840efc98
# Resolve conflicts now

# Commit the files you have modified
$ git add files/with/resolved/conflicts
$ git commit -m 'Backport bde87895c8b1b9df198e3883d24cd9ea840efc98'

Once you have resolved the conflicts as explained above continue with creating a pull request towards the openjdk/jdk17u-dev with the title Backport bde87895c8b1b9df198e3883d24cd9ea840efc98.

Below you can find a suggestion for the pull request body:

Hi all,

This pull request contains a backport of commit bde87895 from the openjdk/jdk repository.

The commit being backported was authored by Wang Zhuo on 26 Jan 2024 and was reviewed by Andrew Haley and Dean Long.

Thanks!

8324123: aarch64: fix prfm literal encoding in assembler

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do not use inline for prfm encoding function

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adding checks in prfm encoding to avoid using pre/post index

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sandlerwang and others added 2 commits January 25, 2024 19:29

Update assembler_aarch64.cpp delete some comments

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Co-authored-by: Andrew Haley <aph-open@littlepinkcloud.com>

Update assembler_aarch64.cpp, merge guarantee

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8324123: aarch64: fix prfm literal encoding in assembler #17482

8324123: aarch64: fix prfm literal encoding in assembler #17482

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8324123: aarch64: fix prfm literal encoding in assembler #17482

8324123: aarch64: fix prfm literal encoding in assembler #17482

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