runtime: gcc_libinit.c _cgo_try_pthread_create 'EAGAIN' undeclared

[kazmccullum]

Problem

Hi, I'm getting the below error when compiling a CGO project.

# runtime/cgo
gcc_libinit.c: In function '_cgo_try_pthread_create':
gcc_libinit.c:106:14: error: 'EAGAIN' undeclared (first use in this function)
   if (err != EAGAIN) {
              ^~~~~~
gcc_libinit.c:106:14: note: each undeclared identifier is reported only once for each function it appears in
gcc_libinit.c:114:1: error: control reaches end of non-void function [-Werror=return-type]

The C code compiles successfully. This seems to be an issue in CGO ?

Some basic investigation

I checked the code in /usr/local/go/src/runtime/cgo/gcc_libinit.c and it does include #include <errno.h>. But still the error 'EAGAIN' undeclared appears.

https://github.com/golang/go/blob/master/src/runtime/cgo/gcc_libinit.c#L9

Workaround

• Adding #define EAGAIN 11 in /usr/local/go/src/runtime/cgo/gcc_libinit.c solves this.

Or,

• Including #include <asm-generic/errno.h> in /usr/local/go/src/runtime/cgo/gcc_libinit.c solves this.

Other details

• OS: Debian 10
• Go version: go version go1.14.6 linux/amd64
• gcc & gccgo version: gcc (Debian 8.3.0-6) 8.3.0

[ianlancetaylor]

The file runtime/cgo/gcc_libinit.c has a line #include <errno.h>. That should be enough to define EAGAIN.