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cmd/link: don't disable memory profiling when pprof.WriteHeapProfile is used

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We have an optimization that if the memory profile is not consumed
anywhere, we set the memory profiling rate to 0 to disable the
"background" low-rate profiling. We detect whether the memory
profile is used by checking whether the runtime.MemProfile function
is reachable at link time. Previously, all APIs that access the
memory profile go through runtime.MemProfile. But the code was
refactored in CL 572396, and now the legacy entry point
WriteHeapProfile uses pprof_memProfileInternal without going
through runtime.MemProfile. In fact, even with the recommended
runtime/pprof.Profile API (pprof.Lookup or pprof.Profiles),
runtime.MemProfile is only (happen to be) reachable through
countHeap.

Change the linker to check runtime.memProfileInternal instead,
which is on all code paths that retrieve the memory profile. Add
a test case for WriteHeapProfile, so we cover all entry points.

Fixes #68136.

Change-Id: I075c8d45c95c81825a1822f032e23107aea4303c
Reviewed-on: https://go-review.googlesource.com/c/go/+/596538
Reviewed-by: Than McIntosh <thanm@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
This commit is contained in:
Cherry Mui 2024-07-03 14:14:34 -04:00
parent 7d19d508a9
commit 82c14346d8
4 changed files with 41 additions and 5 deletions
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4
src/cmd/link/internal/ld/lib.go
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@ -892,9 +892,9 @@ func (ctxt *Link) linksetup() {
}
// Set runtime.disableMemoryProfiling bool if
// runtime.MemProfile is not retained in the binary after
// runtime.memProfileInternal is not retained in the binary after
// deadcode (and we're not dynamically linking).
memProfile := ctxt.loader.Lookup("runtime.MemProfile", abiInternalVer)
memProfile := ctxt.loader.Lookup("runtime.memProfileInternal", abiInternalVer)
if memProfile != 0 && !ctxt.loader.AttrReachable(memProfile) && !ctxt.DynlinkingGo() {
memProfSym := ctxt.loader.LookupOrCreateSym("runtime.disableMemoryProfiling", 0)
sb := ctxt.loader.MakeSymbolUpdater(memProfSym)