1685034 - Avoid sccache hits after clang updates with patches that don't alter the clang binary itself

Status: RESOLVED FIXED

(Firefox Build System :: Toolchains, task)

Description

[Mike Hommey [:glandium]]

See e.g. bug 1588710 for an example of unexpected consequences with a patch that modified clang in a way that should alter the result of the build, but doesn't because of sccache.

Off the top of my head, a solution to this problem would be to
a) make sccache add the contents of the __VERSION__ preprocessor variable to its hash of the compiler (as sccache already invokes the preprocessor, it's a negligible overhead)
b) alter our clang build so that the __VERSION__ preprocessor variable contains something that changes when we have a new build of clang. The hash that is used in the taskcluster index would make sense for that. And it could be added via the CLANG_REVISION define when building clang.

Comment 1

[(Away)]

(In reply to Mike Hommey [:glandium] from comment #0)

The hash that is used in the taskcluster index would make sense for that.

Is there an easy way to take such a hash and map it back to the task ID that ran build-clang? Alternatively, could we use the task ID as the version tag? I've occasionally wanted the ability to take someone's version string and pull up the corresponding build-clang task, in order to look at its logs or download the artifact. (This would be useful on Windows too where we don't have the shared library problem)

Comment 2

[Mike Hommey [:glandium]]

Yeah, in many ways the task id is actually easier. (it's also shorter)

Comment 3

[Mike Hommey [:glandium]]

Attachment: Bug 1685034 - Add the task-id to the clang version.

We hack the clang build system so that the task-id is used for e.g.
CLANG_REVISION, which ends up in e.g. the output of clang --version.

Note that we don't bother with older versions of clang.

Comment 4

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/11810f926917
Add the task-id to the clang version. r=dmajor

Comment 5

[Sandor Molnar[:smolnar]]

https://hg.mozilla.org/mozilla-central/rev/11810f926917

Comment 6

[Mike Hommey [:glandium]]

Attachment: Bug 1685034 - Upgrade sccache to 0.2.15.

The new release contains https://github.com/mozilla/sccache/pull/922

Comment 7

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/f79c3e294cea
Upgrade sccache to 0.2.15. r=firefox-build-system-reviewers,andi,mhentges

Comment 8

[Sandor Molnar[:smolnar]]

https://hg.mozilla.org/mozilla-central/rev/f79c3e294cea

Comment 9

[Narcis Beleuzu [:NarcisB]]

https://hg.mozilla.org/mozilla-central/rev/f79c3e294cea