3 ms·

What's missing to have reproducible builds on PyPI

25 points by Ravencentric 2mo ago

edelbitter 2mo ago
> this file was independently reproduced by <name of trusted party> Sounds risky, unless paired with strong policy about what a verifier should do. e.g. if the verifier just grants network access to the buildbot that then checks what the result should look like, then compromise could remain invisible while the label silently downgrade to "independently downloaded by". And I do not expect there are many parties that would be willing to provide such service beyond their own needs, while simultaneously not already providing that service in places where the infrastructure and policies are already set (such as Debian). Or at least they would already contribute towards build dependencies that do not break reproducibility on every other version bump.
- kpcyrd 2mo ago
  I think running this with network access disabled is a good idea, but it's also important to note "was independently reproduced" is about "we challenged the SBOM and were able to produce this output from the stated inputs". Whether the code in the SBOM subvertly downloads additional code (during build time or later during runtime) is still for the code reviewer to be found.
astralmaster 2mo ago
[flagged]
crabbone 2mo ago
These people are so far gone in their fantasy land... > So we either have to shrug and say, "don't use sdists if you want reproducible builds," What is this, I can't even... How can anyone expect to have a reproducible build's artifact if they downloaded the source? Now, and most importantly, all this talk is about "pure" (as in Python-only) packages. This is, practically, worthless for most real Python projects because those rely on native bindings. Why should anyone expect PyPI to be able to build those if no standard procedure exists for building them is beyond comprehension.
- kpcyrd 2mo ago
  They use the word "Reproducible Builds" for linking the VCS commit to PyPI's repacked source code upload, that's why "reproduce the source code" sounds a little confusing. For projects with native bindings you can still fairly trivially solve this with SBOMs, and some Linux distributions are doing this for many years now. The compiler is a dependency that needs documenting, and they explicitly write they need means to re-create the documented environment from that SBOM.
  - akoboldfrying 2mo ago
    > For projects with native bindings you can still fairly trivially solve this with SBOMs For bitwise identical results there are many small details that need to be taken care of, even in the pure-Python case: Ensuring that files appear in the wheel (zip) file in the same order (glob() doesn't guarantee this and you can definitely see different orders from run to run), timestamps are set to some fixed standard time. Any kind of build-time code generation or pulling in of external info like git commit hashes needs to be handled. Then once you include compiled build dependencies, there might be nondeterminism in the order that a multithreaded compiler writes object code, hidden timestamps, hidden absolute paths, and things like runtime detection of CPU version leading to different instructions being emitted on different machines.
    - kpcyrd 2mo ago
      I'm well aware of those issues (having worked on this for many years), but I still believe the majority of python packages won't be affected by this. :) Most of these you would fix once on the relevant [build-system] and be done with it, no need to fix each individual python library.
  - crabbone 2mo ago
    > fairly trivially solve this with SBOMs Please try building with conda-build to understand the actual problems this entails. Your solution is a fantasy because of how library linkage works. Dynamically loaded libraries need to be able to find each other at runtime. In order to do that, they need to store the location (the filesystem path) to the library they want to load. How these links are resolved is beyond the scope of Python (on Linux, this is managed by ld and ldconf). A lot of Python package maintainers don't understand this problem and don't understand how to make a portable library. Often times builds contain either an absolute path to another library, or a relative path... into nowhere, or a collection of paths... into questionable places. And there's no standard that tells the library authors how to do this the right way. As long as there's no standard, anyone can claim to have done it right and expect their users to accommodate them (which is what currently happens in Python). About your other ideas: making a compiler a dependency is... an awful idea. Unless you can require the same compiler is used for every dependency in your project, at the minimum, you will have an uncontrolled (how are you going to make sure that the right compiler is used to build a package?) zoo of compilers and their versions in your project. In the worst case, compilers will embed their signatures in the generated binary code preventing other binaries from loading such code, if they are generated with a different compiler version (kind of like what happens if you try to load Linux drivers that weren't compiled with the same compiler that compiled the kernel). * * * Like I said: these people have next to no practical experience with the problem they are trying to solve. Why can't they just go some place else and apply themselves elsewhere is beyond my comprehension.
RobertasTa 2mo ago
[flagged]
whateverboat 2mo ago
For python, it seems very difficult to actually do reproducible builds in a way that is useful, because python wheels have very implicit assumptions about paths and environemtns that do not happen anywhere else.
- zejn 2mo ago
  I don't know what your experience is, but I can pack a reproducible AppImage containing a Python virtual environment and it works okay.
  - whateverboat 2mo ago
    Yeah, but then you are packaging the distribution, which is a valid and often a good choice, but then it is not a reproducible wheel anymore.
    - zejn 2mo ago
      I'm not sure I can have reproducible AppImage (SquashFS image) without reproducible wheels?
2hstzAB 2mo ago
[flagged]

25 points by Ravencentric 2mo ago

> this file was independently reproduced by <name of trusted party> Sounds risky, unless paired with strong policy about what a verifier should do. e.g. if the verifier just grants network access to the buildbot that then checks what the result should look like, then compromise could remain invisible while the label silently downgrade to "independently downloaded by". And I do not expect there are many parties that would be willing to provide such service beyond their own needs, while simultaneously not already providing that service in places where the infrastructure and policies are already set (such as Debian). Or at least they would already contribute towards build dependencies that do not break reproducibility on every other version bump.

kpcyrd 2mo ago
I think running this with network access disabled is a good idea, but it's also important to note "was independently reproduced" is about "we challenged the SBOM and were able to produce this output from the stated inputs". Whether the code in the SBOM subvertly downloads additional code (during build time or later during runtime) is still for the code reviewer to be found.

astralmaster 2mo ago

[flagged]

crabbone 2mo ago

These people are so far gone in their fantasy land... > So we either have to shrug and say, "don't use sdists if you want reproducible builds," What is this, I can't even... How can anyone expect to have a reproducible build's artifact if they downloaded the source? Now, and most importantly, all this talk is about "pure" (as in Python-only) packages. This is, practically, worthless for most real Python projects because those rely on native bindings. Why should anyone expect PyPI to be able to build those if no standard procedure exists for building them is beyond comprehension.

kpcyrd 2mo ago
They use the word "Reproducible Builds" for linking the VCS commit to PyPI's repacked source code upload, that's why "reproduce the source code" sounds a little confusing. For projects with native bindings you can still fairly trivially solve this with SBOMs, and some Linux distributions are doing this for many years now. The compiler is a dependency that needs documenting, and they explicitly write they need means to re-create the documented environment from that SBOM.
- akoboldfrying 2mo ago
  > For projects with native bindings you can still fairly trivially solve this with SBOMs For bitwise identical results there are many small details that need to be taken care of, even in the pure-Python case: Ensuring that files appear in the wheel (zip) file in the same order (glob() doesn't guarantee this and you can definitely see different orders from run to run), timestamps are set to some fixed standard time. Any kind of build-time code generation or pulling in of external info like git commit hashes needs to be handled. Then once you include compiled build dependencies, there might be nondeterminism in the order that a multithreaded compiler writes object code, hidden timestamps, hidden absolute paths, and things like runtime detection of CPU version leading to different instructions being emitted on different machines.
  - kpcyrd 2mo ago
    I'm well aware of those issues (having worked on this for many years), but I still believe the majority of python packages won't be affected by this. :) Most of these you would fix once on the relevant [build-system] and be done with it, no need to fix each individual python library.
- crabbone 2mo ago
  > fairly trivially solve this with SBOMs Please try building with conda-build to understand the actual problems this entails. Your solution is a fantasy because of how library linkage works. Dynamically loaded libraries need to be able to find each other at runtime. In order to do that, they need to store the location (the filesystem path) to the library they want to load. How these links are resolved is beyond the scope of Python (on Linux, this is managed by ld and ldconf). A lot of Python package maintainers don't understand this problem and don't understand how to make a portable library. Often times builds contain either an absolute path to another library, or a relative path... into nowhere, or a collection of paths... into questionable places. And there's no standard that tells the library authors how to do this the right way. As long as there's no standard, anyone can claim to have done it right and expect their users to accommodate them (which is what currently happens in Python). About your other ideas: making a compiler a dependency is... an awful idea. Unless you can require the same compiler is used for every dependency in your project, at the minimum, you will have an uncontrolled (how are you going to make sure that the right compiler is used to build a package?) zoo of compilers and their versions in your project. In the worst case, compilers will embed their signatures in the generated binary code preventing other binaries from loading such code, if they are generated with a different compiler version (kind of like what happens if you try to load Linux drivers that weren't compiled with the same compiler that compiled the kernel). * * * Like I said: these people have next to no practical experience with the problem they are trying to solve. Why can't they just go some place else and apply themselves elsewhere is beyond my comprehension.

RobertasTa 2mo ago

[flagged]

whateverboat 2mo ago

For python, it seems very difficult to actually do reproducible builds in a way that is useful, because python wheels have very implicit assumptions about paths and environemtns that do not happen anywhere else.

zejn 2mo ago
I don't know what your experience is, but I can pack a reproducible AppImage containing a Python virtual environment and it works okay.
- whateverboat 2mo ago
  Yeah, but then you are packaging the distribution, which is a valid and often a good choice, but then it is not a reproducible wheel anymore.
  - zejn 2mo ago
    I'm not sure I can have reproducible AppImage (SquashFS image) without reproducible wheels?

2hstzAB 2mo ago

[flagged]