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| author | Michael Anthony Knyszek <mknyszek@google.com> | 2025-11-19 03:51:20 +0000 |
|---|---|---|
| committer | Gopher Robot <gobot@golang.org> | 2025-11-24 13:20:09 -0800 |
| commit | 0bc192368ac603614dc3f240e751f539d91a1db2 (patch) | |
| tree | 9151ab8162d8dfb2f49dda957aaaeb13847fb81e /src/runtime | |
| parent | d4f5650cc5cdc5fa559491991208f8563bd6f3b8 (diff) | |
| download | go-0bc192368ac603614dc3f240e751f539d91a1db2.tar.xz | |
runtime: don't write unique string to trace if it's length zero
While we're here, document that ID 0 is implicitly assigned to an empty
set of data for both stacks and strings.
Change-Id: Ic52ff3a1132abc5a8f6f6c4e4357e31e6e7799fc
Reviewed-on: https://go-review.googlesource.com/c/go/+/723061
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
Auto-Submit: Michael Knyszek <mknyszek@google.com>
Diffstat (limited to 'src/runtime')
| -rw-r--r-- | src/runtime/tracemap.go | 7 | ||||
| -rw-r--r-- | src/runtime/tracestack.go | 9 | ||||
| -rw-r--r-- | src/runtime/tracestring.go | 5 |
3 files changed, 18 insertions, 3 deletions
diff --git a/src/runtime/tracemap.go b/src/runtime/tracemap.go index 9efa325c11..1d6aabb431 100644 --- a/src/runtime/tracemap.go +++ b/src/runtime/tracemap.go @@ -23,6 +23,13 @@ import ( "unsafe" ) +// traceMap is a map of a variable-sized array of bytes to a unique ID. +// +// Because traceMap just operates on raw bytes, this type is used as the +// backing store for both the trace string table and trace stack table, +// the latter of which is just an array of PCs. +// +// ID 0 is reserved for arrays of bytes of size zero. type traceMap struct { root atomic.UnsafePointer // *traceMapNode (can't use generics because it's notinheap) _ cpu.CacheLinePad diff --git a/src/runtime/tracestack.go b/src/runtime/tracestack.go index 51f3c29445..0da217fba9 100644 --- a/src/runtime/tracestack.go +++ b/src/runtime/tracestack.go @@ -136,8 +136,9 @@ func traceStack(skip int, gp *g, tab *traceStackTable) uint64 { return id } -// traceStackTable maps stack traces (arrays of PC's) to unique uint32 ids. -// It is lock-free for reading. +// traceStackTable maps stack traces (arrays of PC's) to unique IDs. +// +// ID 0 is reserved for a zero-length stack. type traceStackTable struct { tab traceMap } @@ -145,8 +146,10 @@ type traceStackTable struct { // put returns a unique id for the stack trace pcs and caches it in the table, // if it sees the trace for the first time. func (t *traceStackTable) put(pcs []uintptr) uint64 { + // Even though put will handle this for us, taking the address of pcs forces a bounds check + // that will fail if len(pcs) == 0. if len(pcs) == 0 { - return 0 + return 0 // ID 0 is reserved for zero-length stacks. } id, _ := t.tab.put(noescape(unsafe.Pointer(&pcs[0])), uintptr(len(pcs))*unsafe.Sizeof(uintptr(0))) return id diff --git a/src/runtime/tracestring.go b/src/runtime/tracestring.go index d486f9efbd..bd31f06a67 100644 --- a/src/runtime/tracestring.go +++ b/src/runtime/tracestring.go @@ -12,6 +12,8 @@ import "internal/trace/tracev2" // traceStringTable is map of string -> unique ID that also manages // writing strings out into the trace. +// +// ID 0 is reserved for the empty string. type traceStringTable struct { // lock protects buf. lock mutex @@ -37,6 +39,9 @@ func (t *traceStringTable) put(gen uintptr, s string) uint64 { // emit emits a string and creates an ID for it, but doesn't add it to the table. Returns the ID. func (t *traceStringTable) emit(gen uintptr, s string) uint64 { + if len(s) == 0 { + return 0 // Empty strings are implicitly assigned ID 0 already. + } // Grab an ID and write the string to the buffer. id := t.tab.stealID() systemstack(func() { |