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package sys
import (
"fmt"
"runtime"
"unsafe"
"github.com/cilium/ebpf/internal/unix"
)
// A sigset containing only SIGPROF.
var profSet unix.Sigset_t
func init() {
// See sigsetAdd for details on the implementation. Open coded here so
// that the compiler will check the constant calculations for us.
profSet.Val[sigprofBit/wordBits] |= 1 << (sigprofBit % wordBits)
}
// maskProfilerSignal locks the calling goroutine to its underlying OS thread
// and adds SIGPROF to the thread's signal mask. This prevents pprof from
// interrupting expensive syscalls like e.g. BPF_PROG_LOAD.
//
// The caller must defer unmaskProfilerSignal() to reverse the operation.
func maskProfilerSignal() {
runtime.LockOSThread()
if err := unix.PthreadSigmask(unix.SIG_BLOCK, &profSet, nil); err != nil {
runtime.UnlockOSThread()
panic(fmt.Errorf("masking profiler signal: %w", err))
}
}
// unmaskProfilerSignal removes SIGPROF from the underlying thread's signal
// mask, allowing it to be interrupted for profiling once again.
//
// It also unlocks the current goroutine from its underlying OS thread.
func unmaskProfilerSignal() {
defer runtime.UnlockOSThread()
if err := unix.PthreadSigmask(unix.SIG_UNBLOCK, &profSet, nil); err != nil {
panic(fmt.Errorf("unmasking profiler signal: %w", err))
}
}
const (
// Signal is the nth bit in the bitfield.
sigprofBit = int(unix.SIGPROF - 1)
// The number of bits in one Sigset_t word.
wordBits = int(unsafe.Sizeof(unix.Sigset_t{}.Val[0])) * 8
)
// sigsetAdd adds signal to set.
//
// Note: Sigset_t.Val's value type is uint32 or uint64 depending on the arch.
// This function must be able to deal with both and so must avoid any direct
// references to u32 or u64 types.
func sigsetAdd(set *unix.Sigset_t, signal unix.Signal) error {
if signal < 1 {
return fmt.Errorf("signal %d must be larger than 0", signal)
}
// For amd64, runtime.sigaddset() performs the following operation:
// set[(signal-1)/32] |= 1 << ((uint32(signal) - 1) & 31)
//
// This trick depends on sigset being two u32's, causing a signal in the
// bottom 31 bits to be written to the low word if bit 32 is low, or the high
// word if bit 32 is high.
// Signal is the nth bit in the bitfield.
bit := int(signal - 1)
// Word within the sigset the bit needs to be written to.
word := bit / wordBits
if word >= len(set.Val) {
return fmt.Errorf("signal %d does not fit within unix.Sigset_t", signal)
}
// Write the signal bit into its corresponding word at the corrected offset.
set.Val[word] |= 1 << (bit % wordBits)
return nil
}
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