gh-142779: Initialize reserved field for proper padding

[stratakis]

The jitdump specification specifies a reserved field for padding.

Initialize it so no garbage data is embedded in the jitdump files.

• Issue: Python/perf_jit_trampoline.c: Header.reserved field uninitialized #142779

[stratakis]

cc @pablogsal

[vstinner]

LGTM

[vstinner]

perf_map_jit_write_header() allocates the header on the stack memory:

static void perf_map_jit_write_header(int pid, FILE* out_file) {
    Header header;        

It's correct to initialize the reserved member to 0. Header structure says:

    uint32_t reserved;           // Reserved field (must be 0)

[miss-islington-app]

Thanks @stratakis for the PR, and @vstinner for merging it 🌮🎉.. I'm working now to backport this PR to: 3.13, 3.14.
🐍🍒⛏🤖

[bedevere-app]

GH-144159 is a backport of this pull request to the 3.14 branch.

[bedevere-app]

GH-144160 is a backport of this pull request to the 3.13 branch.

[vstinner]

Merged, thanks for the fix. I backported the change to 3.13 and 3.14 branches.

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot ARM64 macOS 3.13 (tier-2) has failed when building commit e4e36a7.

What do you need to do:

1. Don't panic.
2. Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
3. Go to the page of the buildbot that failed (https://buildbot.python.org/#/builders/1404/builds/1485) and take a look at the build logs.
4. Check if the failure is related to this commit (e4e36a7) or if it is a false positive.
5. If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/#/builders/1404/builds/1485

Failed tests:

• test_urllib2net

Summary of the results of the build (if available):

==

Click to see traceback logs

remote: Enumerating objects: 4, done.        
remote: Counting objects:  50% (1/2)        
remote: Counting objects: 100% (2/2)        
remote: Counting objects: 100% (2/2), done.        
remote: Total 4 (delta 1), reused 1 (delta 1), pack-reused 2 (from 1)        
From https://github.com/python/cpython
 * branch                    3.13       -> FETCH_HEAD
Note: switching to 'e4e36a716a779887d5b8d2411810a2bec60c4df2'.

You are in 'detached HEAD' state. You can look around, make experimental
changes and commit them, and you can discard any commits you make in this
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do so (now or later) by using -c with the switch command. Example:

  git switch -c <new-branch-name>

Or undo this operation with:

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Turn off this advice by setting config variable advice.detachedHead to false

HEAD is now at e4e36a716a7 [3.13] gh-142779: Initialize reserved field for proper padding (GH-142780) (#144160)
Switched to and reset branch '3.13'

./Modules/selectmodule.c:1988:35: warning: cast from 'PyObject *(*)(PyObject *)' (aka 'struct _object *(*)(struct _object *)') to 'PyCFunction' (aka 'struct _object *(*)(struct _object *, struct _object *)') converts to incompatible function type [-Wcast-function-type-mismatch]
 1988 |     "kqueue_tracking_after_fork", (PyCFunction)kqueue_tracking_after_fork,
      |                                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1 warning generated.

make: *** [buildbottest] Error 2