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// Copyright 2022 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package coverage
import (
"fmt"
"internal/coverage"
"io"
"reflect"
"sync/atomic"
"unsafe"
)
// WriteMetaDir writes a coverage meta-data file for the currently
// running program to the directory specified in 'dir'. An error will
// be returned if the operation can't be completed successfully (for
// example, if the currently running program was not built with
// "-cover", or if the directory does not exist).
func WriteMetaDir(dir string) error {
if !finalHashComputed {
return fmt.Errorf("error: no meta-data available (binary not built with -cover?)")
}
return emitMetaDataToDirectory(dir, getCovMetaList())
}
// WriteMeta writes the meta-data content (the payload that would
// normally be emitted to a meta-data file) for the currently running
// program to the the writer 'w'. An error will be returned if the
// operation can't be completed successfully (for example, if the
// currently running program was not built with "-cover", or if a
// write fails).
func WriteMeta(w io.Writer) error {
if w == nil {
return fmt.Errorf("error: nil writer in WriteMeta")
}
if !finalHashComputed {
return fmt.Errorf("error: no meta-data available (binary not built with -cover?)")
}
ml := getCovMetaList()
return writeMetaData(w, ml, cmode, cgran, finalHash)
}
// WriteCountersDir writes a coverage counter-data file for the
// currently running program to the directory specified in 'dir'. An
// error will be returned if the operation can't be completed
// successfully (for example, if the currently running program was not
// built with "-cover", or if the directory does not exist). The
// counter data written will be a snapshot taken at the point of the
// call.
func WriteCountersDir(dir string) error {
return emitCounterDataToDirectory(dir)
}
// WriteCounters writes coverage counter-data content for
// the currently running program to the writer 'w'. An error will be
// returned if the operation can't be completed successfully (for
// example, if the currently running program was not built with
// "-cover", or if a write fails). The counter data written will be a
// snapshot taken at the point of the invocation.
func WriteCounters(w io.Writer) error {
if w == nil {
return fmt.Errorf("error: nil writer in WriteCounters")
}
// Ask the runtime for the list of coverage counter symbols.
cl := getCovCounterList()
if len(cl) == 0 {
return fmt.Errorf("program not built with -cover")
}
if !finalHashComputed {
return fmt.Errorf("meta-data not written yet, unable to write counter data")
}
pm := getCovPkgMap()
s := &emitState{
counterlist: cl,
pkgmap: pm,
}
return s.emitCounterDataToWriter(w)
}
// ClearCounters clears/resets all coverage counter variables in the
// currently running program. It returns an error if the program in
// question was not built with the "-cover" flag. Clearing of coverage
// counters is also not supported for programs not using atomic
// counter mode (see more detailed comments below for the rationale
// here).
func ClearCounters() error {
cl := getCovCounterList()
if len(cl) == 0 {
return fmt.Errorf("program not built with -cover")
}
if cmode != coverage.CtrModeAtomic {
return fmt.Errorf("ClearCounters invoked for program build with -covermode=%s (please use -covermode=atomic)", cmode.String())
}
// Implementation note: this function would be faster and simpler
// if we could just zero out the entire counter array, but for the
// moment we go through and zero out just the slots in the array
// corresponding to the counter values. We do this to avoid the
// following bad scenario: suppose that a user builds their Go
// program with "-cover", and that program has a function (call it
// main.XYZ) that invokes ClearCounters:
//
// func XYZ() {
// ... do some stuff ...
// coverage.ClearCounters()
// if someCondition { <<--- HERE
// ...
// }
// }
//
// At the point where ClearCounters executes, main.XYZ has not yet
// finished running, thus as soon as the call returns the line
// marked "HERE" above will trigger the writing of a non-zero
// value into main.XYZ's counter slab. However since we've just
// finished clearing the entire counter segment, we will have lost
// the values in the prolog portion of main.XYZ's counter slab
// (nctrs, pkgid, funcid). This means that later on at the end of
// program execution as we walk through the entire counter array
// for the program looking for executed functions, we'll zoom past
// main.XYZ's prolog (which was zero'd) and hit the non-zero
// counter value corresponding to the "HERE" block, which will
// then be interpreted as the start of another live function.
// Things will go downhill from there.
//
// This same scenario is also a potential risk if the program is
// running on an architecture that permits reordering of
// writes/stores, since the inconsistency described above could
// arise here. Example scenario:
//
// func ABC() {
// ... // prolog
// if alwaysTrue() {
// XYZ() // counter update here
// }
// }
//
// In the instrumented version of ABC, the prolog of the function
// will contain a series of stores to the initial portion of the
// counter array to write number-of-counters, pkgid, funcid. Later
// in the function there is also a store to increment a counter
// for the block containing the call to XYZ(). If the CPU is
// allowed to reorder stores and decides to issue the XYZ store
// before the prolog stores, this could be observable as an
// inconsistency similar to the one above. Hence the requirement
// for atomic counter mode: according to package atomic docs,
// "...operations that happen in a specific order on one thread,
// will always be observed to happen in exactly that order by
// another thread". Thus we can be sure that there will be no
// inconsistency when reading the counter array from the thread
// running ClearCounters.
var sd []atomic.Uint32
bufHdr := (*reflect.SliceHeader)(unsafe.Pointer(&sd))
for _, c := range cl {
bufHdr.Data = uintptr(unsafe.Pointer(c.Counters))
bufHdr.Len = int(c.Len)
bufHdr.Cap = int(c.Len)
for i := 0; i < len(sd); i++ {
// Skip ahead until the next non-zero value.
sdi := sd[i].Load()
if sdi == 0 {
continue
}
// We found a function that was executed; clear its counters.
nCtrs := sdi
for j := 0; j < int(nCtrs); j++ {
sd[i+coverage.FirstCtrOffset+j].Store(0)
}
// Move to next function.
i += coverage.FirstCtrOffset + int(nCtrs) - 1
}
}
return nil
}
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