Is there a reason why you don't add "-lpthread" to your cgo linker flags? e.g.

#cgo LDFLAGS: -L./ -lpthread

That is the normal thing to do when linking C code that uses functions from the pthread library.

The main reason I dropped -lpthread" here is that the code in issue can be compiled successfully by original Go compiler.
And gollvm can also succeed when only the pthread_create function is called.

In fact, I have tried to add "-lpthread" to #cgo，and add it to args when compiling middle files with llvm-goc manually
But another error appeared:

# pthread
/home/jxzhang/.local/gollvm/bin/../lib64/libgo.so: error: undefined reference to 'ffi_tramp_is_supported'
/home/jxzhang/.local/gollvm/bin/../lib64/libgo.so: error: undefined reference to 'ffi_tramp_alloc'
/home/jxzhang/.local/gollvm/bin/../lib64/libgo.so: error: undefined reference to 'ffi_tramp_get_addr'
/home/jxzhang/.local/gollvm/bin/../lib64/libgo.so: error: undefined reference to 'ffi_tramp_free'

It seems more difficult...
This error appeared even if I didn't call pthread_join, but I have pulled the latest libffi.
I got nothing about this error on google..

Ok, this part looks actionable. I'll send a CL, thanks.

For the pthread issue, I think this is arising due to differences in the cgo implementations for the main go compiler and gccgo/gollvm. In particular it looks as though we get "-lpthread" vua

https://go.googlesource.com/go/+/1c9e587b90172e7654db897d8c938ffc665e1673/src/runtime/cgo/cgo.go#19

which is not part of the gofrontend version of cgo. I'll ask around about this.

Change https://golang.org/cl/308450 mentions this issue: gollvm: update libgo libffi cmake rules

The gccgo driver program automatically adds -lpthread when linking statically against libgo. When libgo is linked dynamically, it depends on libpthread.so anyhow. So with gccgo programs always have an implicit -lpthread.

Appreciate your help. The latest version works well with such scenario.
I think this issue can be closed, right?

The gccgo driver program automatically adds -lpthread when linking
statically against libgo. When libgo is linked dynamically, it depends
on libpthread.so anyhow. So with gccgo programs always have an
implicit -lpthread.

From what I am seeing gccgo shows the same behavior:

$ which go
/ssd/gcc-trunk/cross/bin/go
# ptgollvm
ccode.c:11: error: undefined reference to 'pthread_join'
collect2: error: ld returned 1 exit status
$ go build -x -gccgoflags=-v . |& fgrep lpthread
$ ldd `which go` | fgrep libgo
	libgo.so.19 => /ssd/gcc-trunk/cross/lib64/libgo.so.19 (0x00007f0d5dcd3000)
$ nm /ssd/gcc-trunk/cross/lib64/libgo.so.19 | fgrep pthread_create
                 w pthread_create
00000000011c0860 t __wrap_pthread_create
$ nm /ssd/gcc-trunk/cross/lib64/libgo.so.19 | fgrep pthread_join
$

It's true that libgo.so depends on libpthread, but this doesn't help resolve the reference to pthread_join at link time.

Ah, interesting. Thanks.

So perhaps the question is whether we should always link against -lpthread, not because we normally need to, but because that is in effect what happens with the gc compiler.