8267908: linux: thread_native_entry can scribble on stack frame

[dholmes-ora]

Please review this trivial fix to ensure we do not try to alloca zero bytes.

Thanks,
David

---

Progress

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Issue

• JDK-8267908: linux: thread_native_entry can scribble on stack frame

Reviewers

• Yasumasa Suenaga (@YaSuenag - Reviewer)

Reviewing

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[mlbridge]

Webrevs

• 00: Full (f2579d82)

[dholmes-ora]

To test this I flipped the ifndef GLIBC to ifdef GLIBC.

[YaSuenag]

Looks good!

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8267908: linux: thread_native_entry can scribble on stack frame

Reviewed-by: ysuenaga

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At the time when this comment was updated there had been 2 new commits pushed to the master branch:

• ae986bc: 8266749: AArch64: Backtracing broken on PAC enabled systems
• 36c4e5f: 8267187: Remove deprecated constructor for Log

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[mlbridge]

Mailing list message from David Holmes on hotspot-runtime-dev:

On 8/06/2021 1:11 pm, Yasumasa Suenaga wrote:

On Tue, 8 Jun 2021 02:02:55 GMT, David Holmes <dholmes at openjdk.org> wrote:

Please review this trivial fix to ensure we do not try to alloca zero bytes.

Thanks,
David

Looks good!

Thanks Yasumasa!

David

[dholmes-ora]

/integrate

[openjdk]

@dholmes-ora Since your change was applied there have been 3 commits pushed to the master branch:

• f40c89e: 8267209: Child threads should defer logging to after child-parent handshake
• ae986bc: 8266749: AArch64: Backtracing broken on PAC enabled systems
• 36c4e5f: 8267187: Remove deprecated constructor for Log

Your commit was automatically rebased without conflicts.

Pushed as commit 341f676.

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

[navyxliu]

When random is 1, that store is still safe because c++ std says sizeof char is 1.

[mlbridge]

Mailing list message from David Holmes on hotspot-runtime-dev:

On 8/06/2021 3:59 pm, Xin Liu wrote:

On Tue, 8 Jun 2021 02:02:55 GMT, David Holmes <dholmes at openjdk.org> wrote:

Please review this trivial fix to ensure we do not try to alloca zero bytes.

Thanks,
David

When random is 1, that store is still safe because c++ std says sizeof char is 1.

The issue was random being zero.

Cheers,
David

[mlbridge]

Mailing list message from David Holmes on hotspot-runtime-dev:

On 8/06/2021 3:59 pm, Xin Liu wrote:

On Tue, 8 Jun 2021 02:02:55 GMT, David Holmes <dholmes at openjdk.org> wrote:

Please review this trivial fix to ensure we do not try to alloca zero bytes.

Thanks,
David

When random is 1, that store is still safe because c++ std says sizeof char is 1.

The issue was random being zero.

Cheers,
David

[navyxliu]

I know. you patch LGTM. that is a side note.

I was worried about this statement was not portable if random is 1.
*(char *)stackmem = 1;

C++ std 6.5.3.4 says:

When sizeof is applied  to  an  operand  that  has  type char, unsigned  char, or signed  char,  (or  a qualified  version  thereof)  the  result  is  1.

Therefore, it's portable.

[mlbridge]

Mailing list message from David Holmes on hotspot-runtime-dev:

On 8/06/2021 4:32 pm, Xin Liu wrote:

On Tue, 8 Jun 2021 02:02:55 GMT, David Holmes <dholmes at openjdk.org> wrote:

Please review this trivial fix to ensure we do not try to alloca zero bytes.

Thanks,
David

I know. you patch LGTM. that is a side note.

I was worried about this statement was not portable if random is 1.
`*(char *)stackmem = 1;`

C++ std 6.5.3.4 says:

When sizeof is applied to an operand that has type char, unsigned char, or signed char, (or a qualified version thereof) the result is 1.

Therefore, it's portable.

Yes it is portable - that was never in question. :)

David

[mlbridge]

Mailing list message from David Holmes on hotspot-runtime-dev:

On 8/06/2021 4:32 pm, Xin Liu wrote:

On Tue, 8 Jun 2021 02:02:55 GMT, David Holmes <dholmes at openjdk.org> wrote:

Please review this trivial fix to ensure we do not try to alloca zero bytes.

Thanks,
David

I know. you patch LGTM. that is a side note.

I was worried about this statement was not portable if random is 1.
`*(char *)stackmem = 1;`

C++ std 6.5.3.4 says:

When sizeof is applied to an operand that has type char, unsigned char, or signed char, (or a qualified version thereof) the result is 1.

Therefore, it's portable.

Yes it is portable - that was never in question. :)

David