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@aerosouund aerosouund commented Jan 6, 2026

Changes

Remove the TODO in the from_bytes_unchecked that concerns the second array initialization during mac address building as the compiler already optimizes it away

Reason

This was an unaddressed todo

// TODO: using something like std::mem::uninitialized could avoid the extra initialization,
// if this ever becomes a performance bottleneck.

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@aerosouund aerosouund marked this pull request as ready for review January 7, 2026 13:03
@JackThomson2
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JackThomson2 commented Jan 7, 2026

I had a quick look in godbolt, it's not apples to apples comparison, but it looks like the compiler was already eliminating this array initialisation: link here The only difference being the range check which was skipped.

I think we can just remove this TODO as it doesn't seem relevant anymore.

Thanks for taking a look!

@aerosouund
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@JackThomson2
Thanks for the clarification. limited the change to just removing the todo

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@aerosouund Great thank you! Can we just have this as a single commit now then looks good to me.

@aerosouund aerosouund changed the title use a maybe uninit in mac address initialization to avoid extra array initialization Remove TODO in from_bytes_unchecked mac address builder Jan 7, 2026
@JackThomson2
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Can we update the commit message to have a shorter title and a small body explaining the change. There's a helpful bit in the contribution guidelines here: https://github.com/firecracker-microvm/firecracker/blob/main/CONTRIBUTING.md#contribution-quality-standards

the from_bytes_unchecked function copies 6 bytes into a new
slice of bytes that is then used as the mac address.
the comment highlighted that the second array memory
initialization should be removed somehow, but the compiler
already optimized it away

Signed-off-by: aerosouund <[email protected]>
@aerosouund
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@JackThomson2
Done, please check

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Looks great thank you

@JackThomson2 JackThomson2 added the Status: Awaiting review Indicates that a pull request is ready to be reviewed label Jan 8, 2026
@JackThomson2 JackThomson2 enabled auto-merge (rebase) January 8, 2026 11:29
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codecov bot commented Jan 8, 2026

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.23%. Comparing base (89702a7) to head (8650c20).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files
@@           Coverage Diff           @@
##             main    #5607   +/-   ##
=======================================
  Coverage   83.23%   83.23%           
=======================================
  Files         277      277           
  Lines       29262    29262           
=======================================
  Hits        24357    24357           
  Misses       4905     4905           
Flag Coverage Δ
5.10-m5n.metal 83.58% <ø> (+<0.01%) ⬆️
5.10-m6a.metal 82.91% <ø> (+<0.01%) ⬆️
5.10-m6g.metal 80.19% <ø> (ø)
5.10-m6i.metal 83.58% <ø> (+<0.01%) ⬆️
5.10-m7a.metal-48xl 82.90% <ø> (ø)
5.10-m7g.metal 80.19% <ø> (ø)
5.10-m7i.metal-24xl 83.54% <ø> (ø)
5.10-m7i.metal-48xl 83.54% <ø> (ø)
5.10-m8g.metal-24xl 80.18% <ø> (ø)
5.10-m8g.metal-48xl 80.18% <ø> (ø)
6.1-m5n.metal 83.60% <ø> (ø)
6.1-m6a.metal 82.94% <ø> (ø)
6.1-m6g.metal 80.18% <ø> (-0.01%) ⬇️
6.1-m6i.metal 83.60% <ø> (-0.01%) ⬇️
6.1-m7a.metal-48xl 82.93% <ø> (ø)
6.1-m7g.metal 80.18% <ø> (-0.01%) ⬇️
6.1-m7i.metal-24xl 83.61% <ø> (ø)
6.1-m7i.metal-48xl 83.61% <ø> (-0.01%) ⬇️
6.1-m8g.metal-24xl 80.18% <ø> (ø)
6.1-m8g.metal-48xl 80.18% <ø> (ø)

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@JackThomson2 JackThomson2 merged commit bc37a09 into firecracker-microvm:main Jan 8, 2026
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4 participants