win32: convert exit codes

Add two utility functions to convert Windows process exit codes.

- exit_code_to_wait_status() converts to a POSIX wait status.
  This is used in ash and the implementations of system(3) and
  mingw_wait3().

- exit_code_to_posix() converts to a POSIX exit code.  (Not that
  POSIX has much to say about them.)

As a result it's possible for more applets to report when child
processes are killed as if by a signal.  'time', 'drop' and 'su -W',
for example.

Adds 64-80 bytes.

6 files changed, 43 insertions, 22 deletions

diff --git a/include/mingw.h b/include/mingw.h
index 1dcc84bde..6ed9bed4a 100644
--- a/include/mingw.h
+++ b/include/mingw.h
@@ -562,6 +562,8 @@ int mingw_execve(const char *cmd, char *const *argv, char *const *envp);
 BOOL WINAPI kill_child_ctrl_handler(DWORD dwCtrlType);
 int kill_signal_by_handle(HANDLE process, int sig);
 int FAST_FUNC is_valid_signal(int number);
+int exit_code_to_wait_status(DWORD win_exit_code);
+int exit_code_to_posix(DWORD win_exit_code);
 
 #define find_mount_point(n, s) find_mount_point(n)
 
diff --git a/loginutils/suw32.c b/loginutils/suw32.c
index 79e8415a8..240a692bc 100644
--- a/loginutils/suw32.c
+++ b/loginutils/suw32.c
@@ -112,6 +112,8 @@ int suw32_main(int argc UNUSED_PARAM, char **argv)
                 WaitForSingleObject(info.hProcess, INFINITE);
                 if (!GetExitCodeProcess(info.hProcess, &r))
                         r = 1;
+                else
+                        r = exit_code_to_posix(r);
                 CloseHandle(info.hProcess);
                 return r;
         }
diff --git a/miscutils/drop.c b/miscutils/drop.c
index 6903254c3..629460564 100644
--- a/miscutils/drop.c
+++ b/miscutils/drop.c
@@ -200,7 +200,7 @@ int drop_main(int argc, char **argv)
                         SetConsoleCtrlHandler(kill_child_ctrl_handler, TRUE);
                         WaitForSingleObject(pi.hProcess, INFINITE);
                         if (GetExitCodeProcess(pi.hProcess, &code)) {
-                                return (int)code;
+                                return exit_code_to_posix(code);
                         }
                 }
         }
diff --git a/shell/ash.c b/shell/ash.c
index dcc73031f..f0480f723 100644
--- a/shell/ash.c
+++ b/shell/ash.c
@@ -4960,7 +4960,7 @@ waitpid_child(int *status, int wait_flags)
         HANDLE *proclist;
         pid_t pid = -1;
         DWORD win_status, idx;
-        int i, sig;
+        int i;
 
         for (jb = curjob; jb; jb = jb->prev_job) {
                 if (jb->state != JOBDONE)
@@ -4992,18 +4992,7 @@ waitpid_child(int *status, int wait_flags)
                                 wait_flags&WNOHANG ? 1 : INFINITE);
         if (idx < pid_nr) {
                 GetExitCodeProcess(proclist[idx], &win_status);
-                if (win_status == 0xc0000005)
-                        win_status = SIGSEGV << 24;
-                else if (win_status == 0xc000013a)
-                        win_status = SIGINT << 24;
-
-                // When a process is terminated as if by a signal the exit
-                // code is zero apart from the signal in its topmost byte.
-                sig = win_status >> 24;
-                if (sig != 0 && win_status == sig << 24 && is_valid_signal(sig))
-                        *status = sig;
-                else
-                        *status = (int)win_status << 8;
+                *status = exit_code_to_wait_status(win_status);
                 pid = pidlist[idx];
         }
  done:
diff --git a/win32/process.c b/win32/process.c
index 2f8b6ce31..54d98e1d9 100644
--- a/win32/process.c
+++ b/win32/process.c
@@ -45,7 +45,7 @@ pid_t mingw_wait3(pid_t pid, int *status, int options, struct rusage *rusage)
                         }
 #endif
                         CloseHandle(proc);
-                        *status = code << 8;
+                        *status = exit_code_to_wait_status(code);
                         return pid;
                 }
         }
@@ -407,7 +407,7 @@ static NORETURN void wait_for_child(HANDLE child)
         SetConsoleCtrlHandler(kill_child_ctrl_handler, TRUE);
         WaitForSingleObject(child, INFINITE);
         GetExitCodeProcess(child, &code);
-        exit((int)code);
+        exit(exit_code_to_posix(code));
 }
 
 int
@@ -807,6 +807,39 @@ int FAST_FUNC is_valid_signal(int number)
         return isalpha(*get_signame(number));
 }
 
+int exit_code_to_wait_status(DWORD exit_code)
+{
+        int sig, status;
+
+        if (exit_code == 0xc0000005)
+                return SIGSEGV;
+        else if (exit_code == 0xc000013a)
+                return SIGINT;
+
+        // When a process is terminated as if by a signal the Windows
+        // exit code is zero apart from the signal in its topmost byte.
+        // This is a busybox-w32 convention.
+        sig = exit_code >> 24;
+        if (sig != 0 && exit_code == sig << 24 && is_valid_signal(sig))
+                return sig;
+
+        // Use least significant byte as exit code, but not if it's zero
+        // and the Windows exit code as a whole is non-zero.
+        status = exit_code & 0xff;
+        if (exit_code != 0 && status == 0)
+                status = 255;
+        return status << 8;
+}
+
+int exit_code_to_posix(DWORD exit_code)
+{
+        int status = exit_code_to_wait_status(exit_code);
+
+        if (WIFSIGNALED(status))
+                return 128 + WTERMSIG(status);
+        return WEXITSTATUS(status);
+}
+
 int kill(pid_t pid, int sig)
 {
         if (sig == SIGKILL || sig == 0)
diff --git a/win32/system.c b/win32/system.c
index 00b594242..c718d9948 100644
--- a/win32/system.c
+++ b/win32/system.c
@@ -6,7 +6,6 @@ int mingw_system(const char *cmd)
         intptr_t proc;
         HANDLE h;
         DWORD ret = 0;
-        int sig;
 
         if (cmd == NULL)
                 return 1;
@@ -19,9 +18,5 @@ int mingw_system(const char *cmd)
         GetExitCodeProcess(h, &ret);
         CloseHandle(h);
 
-        // Was process terminated as if by a signal?
-        sig = ret >> 24;
-        if (sig != 0 && ret == sig << 24 && is_valid_signal(sig))
-                return sig;
-        return ret << 8;
+        return exit_code_to_wait_status(ret);
 }