RFC: Add compiler support for instrumenting functions#3917
RFC: Add compiler support for instrumenting functions#3917pmur wants to merge 4 commits intorust-lang:masterfrom
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text/0000-instrumented-functions.md
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| * [XRay](https://llvm.org/docs/XRay.html), an LLVM project to instrument both entry and exit of functions, | ||
| with dynamic enablement. | ||
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| These features are all very similar, are effectively mutually exclusive (e.g., mcount and fentry). |
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| These features are all very similar, are effectively mutually exclusive (e.g., mcount and fentry). | |
| These features are all very similar, and are effectively mutually exclusive (e.g., mcount and fentry). |
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| ### Language additions | ||
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| A single builtin attribute, `instrument_fn`, will be added. It will be applied to functions and methods |
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maybe there should be #[instrument_fn = "off"] or similar to opt out of all function instrumentation, not just entry/exit (you mentioned loop instrumentation earlier), that would be useful when implementing the instrumentation function to avoid recursively calling itself.
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For usability, that seems nice for most common cases. I'll add it.
As for ignore-loops, it is an xray option to modify its heuristics for deciding to whether to instrument the function. I wonder if there is a case where you want to instrument more than *logues, but less than every basic block.
ehuss
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T-lang
| ## Prior art | ||
| [prior-art]: #prior-art |
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How does this related to RFC patchable-function-entry by @maurer ?
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For linux ftrace, both provide similar features. Though, x86-64 seems to support both, and some distros use both. I am curious why.
For using existing instrumentation frameworks like gprof or xray, there are more expectations beyond inserting and tracking nops at entry.
* Add `#[instrument_fn = "off"]` form. * s/linux/Linux/ when used as a proper noun. * Add prior art paragraph about patachable-function-entries rfc. * Clarify `ignore-loops` xray option.
With the current instrumentation frameworks, I don't think there is benefit to fine grain controls. I have simplified the attribute to "on" and "off". XRay has some creative options, but fine grain control of entry and exit instrumentation insertion probably isn't useful.
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This RFC proposes to add support for instrumenting function calls using mcount fentry or xray, and adding a new builtin attribute to toggle instrumentation.
Today, mcount and xray enjoy experimental support, but I was unable to find any RFC proposing their inclusion.
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