posix-spawn/run fail to run, no output on CentOS 7

[jminh]

On CentOS 7, below simple program is failing to run. There is no output on
CentOS 7.

$ cat hello.janet
#!/usr/bin/env janet
(import posix-spawn)

(posix-spawn/run ["ls"])

$ ./hello.janet

$ lsb_release -a
LSB Version:    :core-4.1-amd64:core-4.1-ia32:core-4.1-noarch:cxx-4.1-amd64:cxx-4.1-ia32:cxx-4.1-noarch:desktop-4.1-amd64:desktop-4.1-ia32:desktop-4.1-noarch:languages-4.1-amd64:languages-4.1-noarch:printing-4.1-amd64:printing-4.1-noarch
Distributor ID: CentOS
Description:    CentOS Linux release 7.3.1611 (Core)
Release:        7.3.1611
Codename:       Core

From strace we can see there is no relevant system call like clone, fork or
vfork.

$ strace -ff -eprocess -o x ./hello.janet

$ cat x.147015
execve("./hello.janet", ["../hello.janet"], [/* 94 vars */]) = 0
arch_prctl(ARCH_SET_FS, 0x7ffff7f9f740) = 0
execve("/path/to/janet", ["janet", "./hello.janet"], [/* 94 vars */]) = 0
arch_prctl(ARCH_SET_FS, 0x7ffff7f9e140) = 0
clone(child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0x7ffff7f9e410) = 147016
wait4(147016, [{WIFEXITED(s) && WEXITSTATUS(s) == 127}], 0, NULL) = 147016
--- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=147016, si_status=127, si_utime=0, si_stime=0} ---
exit_group(0)                           = ?
+++ exited with 0 +++

$ cat x.147016
exit_group(127)                         = ?
+++ exited with 127 +++

[jminh]

I've tried gdb to check what's going on but didn't find useful information.
While reading the posix_spawn document
(https://man7.org/linux/man-pages/man3/posix_spawn.3.html) , in the "Program
source" I noticed POSIX_SPAWN_SETSIGMASK as follows:

  s = posix_spawnattr_setflags(&attr, POSIX_SPAWN_SETSIGMASK);

Based on the descriptoin we should use this flag when we want to set sigmask.

With that, I have a patch as shown below to correctly run ls command. strace
also show there is a clone system call.

--- a/posix-spawn.c
+++ b/posix-spawn.c
@@ -371,6 +371,10 @@ static Janet primitive_pspawn(int32_t argc, Janet *argv) {
     SIGSETARG(sig_mask_set, 7);
 #undef SIGSETARG

+    if (posix_spawnattr_setflags(pattr, POSIX_SPAWN_SETSIGMASK) != 0) {
+        PSPAWN_ERROR("unable to setflags");
+    }
+
     if (posix_spawnattr_setsigdefault(pattr, &sig_dflt_set) != 0) {
         PSPAWN_ERROR("unable to sig default");
     }

$ strace -ff -eprocess -o x ./run.janet

$ cat x.143501
execve("./hello.janet", ["./hello.janet"], [/* 94 vars */]) = 0
arch_prctl(ARCH_SET_FS, 0x7ffff7f9f740) = 0
execve("/path/to/janet", ["janet", "./hello.janet"], [/* 94 vars */]) = 0
arch_prctl(ARCH_SET_FS, 0x7ffff7f9e140) = 0
clone(child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0x7ffff7f9e410) = 143503
wait4(143503, [{WIFEXITED(s) && WEXITSTATUS(s) == 0}], 0, NULL) = 143503
--- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=143503, si_status=0, si_utime=0, si_stime=0} ---
exit_group(0)                           = ?
+++ exited with 0 +++

$ grep '= 0' x.143503
execve("/usr/local/bin/ls", ["ls"], [/* 94 vars */]) = 0
arch_prctl(ARCH_SET_FS, 0x7ffff7f9c840) = 0

[jminh]

The proposal fix also resolves the issue
andrewchambers/janet-sh#20 .