go runtime sets its own signal handlers

go runtime sets its own signal handlers.md

go runtime sets its own signal handlers

By default go sets its own signal handlers:

• runtime.mstart0() -> runtime.mstart1()
• runtime.mstart1() -> runtime.mstartm0()
• runtime.mstartm0() -> runtime.initsig()
• runtime.initsig() -> runtime.setsig(i, abi.FuncPCABIInternal(sighandler))

Another way to confirm this:

Dockerfile:

FROM alpine:3.20
COPY a.go .
RUN apk add go strace \
    && GO111MODULE=off go build \
    && strace ./_ 2>&1 | grep -E 'sigaction.*TERM|hello'

a.go:

package main
import "fmt"
func main() {
    fmt.Printf("hello world")
}

$ docker build .
rt_sigaction(SIGTERM, NULL, {sa_handler=SIG_DFL, sa_mask=[], sa_flags=0}, 8) = 0
rt_sigaction(SIGTERM, {sa_handler=0x463de0, sa_mask=~[], sa_flags=SA_RESTORER|SA_ONSTACK|SA_RESTART|SA_SIGINFO, sa_restorer=0x463f20}, NULL, 8) = 0
write(1, "hello world", 11hello world)             = 11

To inspect the code with a debugger:

$ docker run --rm -it alpine:3.20
/ # apk add go
/ # go install github.com/go-delve/delve/cmd/dlv@latest
/ # GO111MODULE=off ~/go/bin/dlv debug
Type 'help' for list of commands.
(dlv) b initsig
Breakpoint 1 set at 0x44f464 for runtime.initsig() .usr/lib/go/src/runtime/signal_unix.go:114
(dlv) c
> [Breakpoint 1] runtime.initsig() .usr/lib/go/src/runtime/signal_unix.go:114 (hits total:1) (PC: 0x44f464)
Warning: debugging optimized function
   109: // Initialize signals.
   110: // Called by libpreinit so runtime may not be initialized.
   111: //
   112: //go:nosplit
   113: //go:nowritebarrierrec
=> 114: func initsig(preinit bool) {
   115:         if !preinit {
   116:                 // It's now OK for signal handlers to run.
   117:                 signalsOK = true
   118:         }
   119:
(dlv)

The table that defines what to do with each signal.