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cmd/go: stamp git/vcs current HEAD hash/commit hash/dirty bit in binaries #37475

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bradfitz opened this issue Feb 26, 2020 · 22 comments
Open

cmd/go: stamp git/vcs current HEAD hash/commit hash/dirty bit in binaries #37475

bradfitz opened this issue Feb 26, 2020 · 22 comments

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@bradfitz
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@bradfitz bradfitz commented Feb 26, 2020

(Related but different than #35667)

cmd/go currently embeds all the module dep information in binaries and it's readable with e.g. https://godoc.org/rsc.io/goversion/version but it does not include any information about the top-level module's version.

I propose that cmd/go look at {git,svn,etc} state and include in the binary:

  • HEAD commit time
  • HEAD hash
  • dirty bit (if there are uncommitted changes)

Currently many projects do this by hand with a build-program.sh and stamping it manually with --ldflags=-X foo=bar, but that means programs built the normal Go way lack that information, and people end up with non-portable (shell, often) build scripts.

I've hit this enough times with my own projects that it's actively frustrating me. It's worse when programs are clients that want to report their version number to a server (which might want to do analytics, build horizon enforcement, protocol version negotiation, etc) and then can't. There are alternative ways to do all that, but they're tedious.

Mostly I'm concerned that people have bespoke, often non-portable build scripts.

@bradfitz bradfitz added the Proposal label Feb 26, 2020
@gopherbot gopherbot added this to the Proposal milestone Feb 26, 2020
@rsc rsc added this to Incoming in Proposals Feb 26, 2020
@rsc rsc moved this from Incoming to Active in Proposals Feb 26, 2020
@bcmills
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@bcmills bcmills commented Feb 26, 2020

This may be a duplicate of #29814.

bradfitz added a commit to tailscale/tailscale that referenced this issue Feb 28, 2020
Maybe we'll auto-bump this with a bot over time.

See golang/go#37475 & golang/go#29814

Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
@rsc
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@rsc rsc commented Mar 4, 2020

We should figure out exactly what we want to record.
The other modules are all versions or pseudo-versions.
Should this one be too?
Can we find that quickly enough to be reasonable to run during every 'go build'?
(We can skip it during 'go test' like we skip dwarf.)
The go command already has code to turn a commit hash into a version; we should probably just use that same code and add a +modified if the working directory is modified.

It would be helpful to time how much overhead this would be in 'go build'.

@bcmills, do you have any numbers about how much time this would add?

@rsc
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@rsc rsc commented Mar 4, 2020

BTW I agree it's a duplicate of #29814 but I'll keep using this one because it is marked as a proposal and already appeared in the minutes.

@bcmills
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@bcmills bcmills commented Mar 4, 2020

It would be helpful to time how much overhead this would be in 'go build'.

git status --porcelain=v2 in the go repository is around 50ms for me, and git log -n 1 is around 25ms.

go install cmd/go for me is 1.6s dirty, and 140ms clean. So assuming that we can run the VCS commands in parallel with builds for non-main packages, the latency hit should be negligible.

CC @jayconrod @matloob

@bcmills
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@bcmills bcmills commented Mar 4, 2020

Hmm, I realized that I didn't account for checking tags in the above calculations. Still, I expect those costs will be order-of-magnitude similar to any other git command.

@dottedmag
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@dottedmag dottedmag commented Mar 4, 2020

I'd like to point out a (maybe small) problem with this approach: changing the version of source code, but not the code itself will cause the binary to change.

Let me explain the use-case I have that will be broken by this change:

  • A number of binaries are built from a monorepo, each binary is packaged in Docker, and a Helm chart is generated for every binary. This chart includes Docker image ID, not the tag.
  • These Helm charts are installed to Kubernetes

If the Helm chart contents and the binaries don't change, then no upgrades are performed by Kubernetes.

If the version of the checkout is stamped into every Go binary, then this scheme crumbles and:

  • either a version needs to be purged from every binary before packaging it into a Docker image,
  • or some crazy scheme has to be invented: remove the version from the binary, take a checksum, check that there is no Docker image with this version as a label published in the registry, publish the image and label it, use this label in Helm charts.
@bradfitz
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@bradfitz bradfitz commented Mar 5, 2020

@dottedmag, what if we made it conditional on importing a new package, say runtime/version, containing the accessor funcs to get at the info? Then if you don't use it, no change in behavior.

Would that work for your use case?

@mark-rushakoff
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@mark-rushakoff mark-rushakoff commented Mar 5, 2020

I'm in a practically identical case to @dottedmag.

Inevitably, somewhere in the monorepo we will (perhaps unintentionally) bring in a dependency that depends on a magic package that breaks deterministic builds.

I think for most common cases, having this proposal enabled by default would be preferable. For my use case, I would be satisfied if there was a documented way to opt out of it. We already are using -ldflags=-buildid= to force a consistent build ID as part of deterministic binaries, so another esoteric flag to opt out of recording VCS state would be completely acceptable.

@dottedmag
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@dottedmag dottedmag commented Mar 5, 2020

@dottedmag, what if we made it conditional on importing a new package, say runtime/version, containing the accessor funcs to get at the info? Then if you don't use it, no change in behavior.

I agree with @mark-rushakoff: relying on imports will be brittle unless this import is considered only for main packages.

It's not an author of some recursively included library, but a builder of a final binary who in a position to decide whether to put versioning information into the binary or not.

@bcmills
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@bcmills bcmills commented Mar 5, 2020

@dottedmag, note that many functionally-equivalent builds will already produce slightly different binaries due to the version-stamping for runtime/debug.ReadBuildInfo. The version stamps will change with each change to the corresponding module versions, even if the contents of the specific imported packages are the same.

This proposal would case more of the same sort of version churn, but it is fundamentally the same churn.

That suggests that we may want to provide an option to disable version stamping in general. IMO, that should be a separate proposal.

@dottedmag
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@dottedmag dottedmag commented Mar 5, 2020

True. In practice, it is not a problem as changing the versions of dependencies nearly always changes the code of dependencies — nobody is updating versions of dependencies endlessly for no reason, usually, they only get updated to get a new feature or a bugfix.

Filed #37693.

@rsc
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@rsc rsc commented Mar 25, 2020

The discussion above about reproducible builds sounds like it would be satisfied by having the version embedded by default but also having an opt-out command-line flag; no special package needed.

Do I have that right, @dottedmag and @mark-rushakoff?

@mark-rushakoff
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@mark-rushakoff mark-rushakoff commented Mar 25, 2020

Yes, I think a flag to opt out of embedding version details would suffice for reproducible builds.

It would be nice if there was a single flag like -reproducible to omit version details and to set a fixed build ID, but it is probably fine if those remain separate concerns.

I don't care about reproducible builds when I'm at the command line building something for my own use; I care about reproducible builds when I am writing build scripts that run as part of a CI/CD pipeline, so it is not a big deal if I need to look up the whole collection of settings to make those builds reproducible.

@dottedmag
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@dottedmag dottedmag commented Mar 25, 2020

@rsc Correct.

@rsc
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@rsc rsc commented Apr 1, 2020

OK, it sounds like everyone agrees about doing this by default, with a flag to turn it off.
It is unclear exactly how fast it will be to ask git/etc what we need to know, but that operation can overlap with the entire build, including the link. Right now if I build helloworld I get:

/Users/rsc/go/pkg/tool/darwin_amd64/link -o $WORK/b001/exe/a.out -importcfg $WORK/b001/importcfg.link -buildmode=exe -buildid=SqhXBrEZODPkt1gG-6fj/H70nrokRrHQB9NgKyehx/mN9hM1-9avNnPeQfRwgY/SqhXBrEZODPkt1gG-6fj -extld=clang $WORK/b001/_pkg_.a
/Users/rsc/go/pkg/tool/darwin_amd64/buildid -w $WORK/b001/exe/a.out # internal

That buildid step could install the git version info too. I'm confident git will be faster than the link.

Based on the discussion, then, this seems like a likely accept, although we may not be able to implement it until the next release (Go 1.16).

@rsc rsc moved this from Active to Likely Accept in Proposals Apr 1, 2020
@seankhliao
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@seankhliao seankhliao commented Apr 1, 2020

Will this include just the commit hash or also a (any?) version tag

@liggitt
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@liggitt liggitt commented Apr 1, 2020

Version tags introduce many sharp edges, at least for git… since you can have a git repo cloned without having fetched all tags, or can have different local tags, or can add a tag to a SHA at any point in time, using the nearest tag (e.g. git describe or equivalent) would mean that a build of the same SHA could result in different embedded versions for different people (or for the same person at different times). Further, if the closest tagged commit has multiple tags associated with it, the version could be ambiguous (git describe has particularly unpredictable behavior in this case).

@bcmills
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@bcmills bcmills commented Apr 1, 2020

@liggitt, note that that problem only occurs in one direction. (It is fine in general to have N names for one commit. The important property is that we resolve only one commit for a given name.)

The go command already has an algorithm for inferring the canonical name for a given repo state, implemented as part of #27171. (Specifically, we infer either the highest tagged semantic version appropriate to the module path, or a pseudo-version derived from the highest-tagged ancestor.)

I realize that that algorithm makes things awkward for the k8s.io repos in particular because of their unusual tagging history (in which v1.5.1 is an ancestor of v0.18.0), but from what we've observed that sort of nonlinear history is an outlier.

@liggitt
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@liggitt liggitt commented Apr 1, 2020

The important property is that we resolve only one commit for a given name.

Since tags can be local, preferring a tag over a sha would mean two users could have identical local tags associated with different SHAs. Or are you suggesting the mapping of shas to tags would not be determined by consulting the local VCS, but the remote canonical VCS?

@bcmills
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@bcmills bcmills commented Apr 1, 2020

That seems like a reasonable motivation to include both the commit hash and semantic version, rather than just one or the other.

@rsc
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@rsc rsc commented Apr 8, 2020

No change in consensus, so accepted. We may still need to work out exactly what to include, but everyone seems to agree that this is worth doing (barring some discovery about it being more expensive than we think).

@rsc rsc moved this from Likely Accept to Accepted in Proposals Apr 8, 2020
@rsc rsc modified the milestones: Proposal, Backlog Apr 8, 2020
@rsc rsc changed the title proposal: cmd/go: stamp git/vcs current HEAD hash/commit hash/dirty bit in binaries cmd/go: stamp git/vcs current HEAD hash/commit hash/dirty bit in binaries Apr 8, 2020
bradfitz added a commit to tailscale/go that referenced this issue Apr 16, 2020
bradfitz added a commit to tailscale/go that referenced this issue Jun 14, 2020
@jayconrod
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@jayconrod jayconrod commented Jun 24, 2020

Tentatively marking this for 1.16. We'll try to get this in, but we have a lot planned, and I can't promise it will get done. If someone is interested in working on this, I'll sketch out what needs to be done. This is complicated though, so probably not a good first issue.

  • Most of our VCS code for fetching modules is in cmd/go/internal/modfetch/codehost. It's fairly specific to modules and not intended to work with local repositories. Not sure whether it would be better to generalize that package and add support there or in a new package. I'd start with the former and see how complicated it gets.
    • In any case, there should be something the rest of cmd/go can call that returns VCS information.
    • That should support git, hg, svn, bzr, and fossil.
  • This information should be saved in cmd/go/internal/load.PackageInternal.BuildInfo. We use that field to store module information that's stamped into main packages. Since it would no longer be module-specific, it would need to be generalized.
    • Something in cmd/go/internal/load should populate that field for main packages, combining information with modload.PackageBuildInfo. This is currently done in Package.load. Note that different main packages in the same build may belong to different repositories.
    • BuildInfo is already part of the package cache key, so when it's changed, it would already cause cached main packages to become stale. We should make sure to test that though.
    • The code that does the stamping in cmd/go/internal/work.Builder.build is module-specific and would need adjustment.
  • runtime/debug.BuildInfo will need new fields, and runtime/debug.ReadBuildInfo will need to populate them.
  • cmd/go/internal/version will also need to be able to read and report the new information. Not clear to me if this should be printed by default or behind a flag (similar to how module information is behind -m). Probably the latter.
  • In #39301, we should move the code that extracts build information to x/mod. That would need to support this as well.
alexmv added a commit to alexmv/smokescreen that referenced this issue Aug 31, 2020
The `$Id$` which can be auto-expanded in files via the `ident`
attribute does not function the same as the old CVS `$Id$` keyword.
In CVS, the keyword expansion was updated on every commit, to contain
the current commit id.  In git, it is expanded with the identifier of
the _blob it is found in_.  That is, previous to this commit, the
`$Id$` (and hence the reported "version hash") was
f220e479c5d8d85c7b753e95dc5fe0b67bbfbd38 -- and had been since the
file was changed last, in f386360.

Remove the misleading hash, and attendant git attributes file.  It
will frequently mislead callers that the version has not changed
when, in reality, it has.

Git itself does not have a way to embed "the current commit hash" into
a file in a way that is updated whenever the commit changes.  Nor does
Go natively have a way to embed it into the binary at build time,
though this may change in the future[1].

As alluded to in that ticket, most projects elect to pass in the
build-time commit information via something like:
```
GIT_COMMIT=$(git rev-parse HEAD)
go build -ldflags "-X main.gitCommit=$(GIT_COMMIT)"
```

However, smokescreen does not currently have any build system external
to `go build` which could embed the above logic.  Rather than choose a
build system and introduce a new dependency, remove the misleading
hash entirely.

[1] golang/go#37475 and also
    golang/go#29228
mvdan added a commit to burrowers/garble that referenced this issue Sep 22, 2020
As per the discussion in golang/go#41145, it
turns out that we don't need special support for build caching in
-toolexec. We can simply modify the behavior of "[...]/compile -V=full"
and "[...]/link -V=full" so that they include garble's own version and
options in the build cache key.

We add a number of things to the -V=full output. First, "+garble" since
that is the relatively unique name of the Go program. Second, the
version of Garble itself. Since we can't do this via modules until
golang/go#37475, we instead use the
hex-encoded sha256 of our own binary.

Finally, we need to add the garble options which modify how we obfuscate
code, since each should result in different build cache keys. GOPRIVATE
also affects caching, since a different GOPRIVATE value means that we
might have to garble a different set of packages.

This feature works, with only a minor regression in the ldflags test
since the -X linker flag is now broken with private names. The following
commit will fix that.
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