avoid breaking intrinsics when obfuscating names #655
Merged
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
We obfuscate import paths as well as their declared names. The compiler treats some packages and APIs in special ways, and the way it detects those is by looking at import paths and names. In the past, we have avoided obfuscating some names like embed.FS or reflect.Value.MethodByName for this reason. Otherwise, go:embed or the linker's deadcode elimination might be broken. This matching by path and name also happens with compiler intrinsics. Intrinsics allow the compiler to rewrite some standard library calls with small and efficient assembly, depending on the target GOARCH. For example, math/bits.TrailingZeros32 gets replaced with ssa.OpCtz32, which on amd64 may result in using the TZCNTL instruction. We never noticed that we were breaking many of these intrinsics. The intrinsics for funcs declared in the runtime and its dependencies still worked properly, as we do not obfuscate those packages yet. However, for other packages like math/bits and sync/atomic, the intrinsics were being entirely disabled due to obfuscated names. Skipping intrinsics is particularly bad for performance, and it also leads to slightly larger binaries: │ old │ new │ │ bin-B │ bin-B vs base │ Build-16 5.450Mi ± ∞ ¹ 5.333Mi ± ∞ ¹ -2.15% (p=0.029 n=4) Finally, the main reason we noticed that intrinsics were broken is that apparently GOARCH=mips fails to link without them, as some symbols end up being not defined at all. This patch fixes builds for the MIPS family of architectures. Rather than building and linking all of std for every GOARCH, test that intrinsics work by asking the compiler to print which intrinsics are being applied, and checking that math/bits gets them. This fix is relatively unfortunate, as it means we stop obfuscating about 120 function names and a handful of package paths. However, fixing builds and intrinsics is much more important. We can figure out better ways to deal with intrinsics in the future. Fixes burrowers#646.
|
@capnspacehook we might want to obfuscate import paths at link time rather than at compile time, after all! |
pagran
approved these changes
Jan 25, 2023
|
Nice :) |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
(see commit message)
Fixes #646.