Restore build on old systems without openat(2) (re: 3d7b7e1)

The openat system call was standardised by POSIX in 2008, which is
still too recent for it to be portable on systems older than a
decade or so. I have two old systems that it breaks on.

src/lib/libast/features/lib:
- Add simple lib test for openat(2), defining _lib_openat if found.
  This will be available wherever <ast.h> is included.

src/cmd/ksh93/*/*.[ch]:
- Restore the tried-and-tested cd_pwd.c and subshell.c code from
  before the referenced commit as a fallback for systems that don't
  have openat(2), i.e.: it is used #if !_lib_openat.
- However, the even older pre-fchdir(2) code is not restored.

Additionally, a couple of build system workarounds for old systems:

src/cmd/INIT/mamake.c:
- Do not set fictional future _POSIX_SOURCE and _X_OPEN_SOURCE
  version macros. The system headers on (at least) QNX 6.5.0 and
  Solaris 10.1 don't like them. (re: f58153d)
src/cmd/INIT/include/link_ar.mam:
- Compensate for the lack of 'ar -s' by falling back to pre-POSIX
  'ranlib'. Solaris 10.1 needs this. (re: 2ad0f54)

Resolves: ksh93#816

src/cmd/INIT/include/link_ar.mam

@@ -42,4 +42,4 @@ exec -	esac
 note *	Some old systems do not automatically update the symbol table upon ad
 note *	adding or deleting object files (contra POSIX), so update it manually
 
-exec -	%{AR} -s %{@}
+exec -	%{AR} -s %{@} 2>/dev/null || ranlib %{@} 2>/dev/null || true

src/cmd/INIT/mamake.c

@@ -112,8 +112,6 @@ static const char usage[] =
  * must be enabled to prevent the build from failing at the very start.
  */
 
-#define _POSIX_C_SOURCE 21000101L	/* generic */
-#define _XOPEN_SOURCE	9900		/* generic */
 #define _DARWIN_C_SOURCE 1		/* macOS */
 #define _GNU_SOURCE 1			/* GNU/Linux, Cygwin */
 #define _FILE_OFFSET_BITS 64		/* 32-bit Linux 5.6+ (glibc 2.32+) */

src/cmd/ksh93/bltins/cd_pwd.c

@@ -46,6 +46,7 @@ static void rehash(Namval_t *np,void *data)
 		nv_rehash(np,data);
 }
 
+#if _lib_openat
 /*
  * Obtain a file handle to the directory "path" relative to directory "dir"
  */
@@ -62,6 +63,7 @@ int sh_diropenat(int dir, const char *path)
 	close(fd);
 	return shfd;
 }
+#endif /* _lib_openat */
 
 int	b_cd(int argc, char *argv[],Shbltin_t *context)
 {
@@ -70,9 +72,11 @@ int	b_cd(int argc, char *argv[],Shbltin_t *context)
 	const char *dp;
 	int saverrno=0;
 	int rval,pflag=0,eflag=0,ret=1;
-	int newdirfd;
 	char *oldpwd, *cp;
 	Namval_t *opwdnod, *pwdnod;
+#if _lib_openat
+	int newdirfd;
+#endif /* _lib_openat */
 	NOT_USED(context);
 	while((rval = optget(argv,sh_optcd))) switch(rval)
 	{
@@ -136,8 +140,13 @@ int	b_cd(int argc, char *argv[],Shbltin_t *context)
 	 * If sh_subshell() in subshell.c cannot use fchdir(2) to restore the PWD using a saved file descriptor,
 	 * we must fork any virtual subshell now to avoid the possibility of ending up in the wrong PWD on exit.
 	 */
+#if _lib_openat
 	if(sh.subshell && !sh.subshare && (!sh_validate_subpwdfd() || !test_inode(sh.pwd,e_dot)))
 		sh_subfork();
+#else
+	if(sh.subshell && !sh.subshare && !test_inode(sh.pwd,e_dot))
+		sh_subfork();
+#endif /* _lib_openat */
 	/*
 	 * Do $CDPATH processing, except if the path is absolute or the first component is '.' or '..'
 	 */
@@ -157,7 +166,6 @@ int	b_cd(int argc, char *argv[],Shbltin_t *context)
 	if(*dir!='/')
 	{
 		/* check for leading .. */
-		char *cp;
 		sfprintf(sh.strbuf,"%s",dir);
 		cp = sfstruse(sh.strbuf);
 		pathcanon(cp, 0);
@@ -199,6 +207,7 @@ int	b_cd(int argc, char *argv[],Shbltin_t *context)
 				if(!pathcanon(cp,PATH_DOTDOT))
 					continue;
 		}
+#if _lib_openat
 		cp = path_relative(stkptr(sh.stk,PATH_OFFSET));
 		rval = newdirfd = sh_diropenat((sh.pwdfd>0)?sh.pwdfd:AT_FDCWD,cp);
 		if(newdirfd>0)
@@ -217,10 +226,17 @@ int	b_cd(int argc, char *argv[],Shbltin_t *context)
 #endif
 		if(saverrno==0)
 			saverrno=errno;
+#else
+		if((rval=chdir(path_relative(stkptr(sh.stk,PATH_OFFSET)))) >= 0)
+			goto success;
+		if(errno!=ENOENT && saverrno==0)
+			saverrno=errno;
+#endif /* _lib_openat */
 	}
 	while(cdpath);
 	if(rval<0 && *dir=='/' && *(path_relative(stkptr(sh.stk,PATH_OFFSET)))!='/')
 	{
+#if _lib_openat
 		rval = newdirfd = sh_diropenat((sh.pwdfd>0)?sh.pwdfd:AT_FDCWD,dir);
 		if(newdirfd>0)
 		{
@@ -236,6 +252,9 @@ int	b_cd(int argc, char *argv[],Shbltin_t *context)
 		else if((rval=chdir(dir)) >= 0)
 			sh_pwdupdate(sh_diropenat(AT_FDCWD,dir));
 #endif
+#else
+		rval = chdir(dir);
+#endif /* _lib_openat */
 	}
 	if(rval<0)
 	{

src/cmd/ksh93/include/defs.h

@@ -114,7 +114,6 @@ extern char		*sh_checkid(char*,char*);
 extern void		sh_chktrap(void);
 extern void		sh_deparse(Sfio_t*,const Shnode_t*,int,int);
 extern int		sh_debug(const char*,const char*,const char*,char *const[],int);
-extern int		sh_diropenat(int,const char *);
 extern char 		**sh_envgen(void);
 extern Sfdouble_t	sh_arith(const char*);
 extern void		*sh_arithcomp(char*);
@@ -142,15 +141,18 @@ extern Dt_t		*sh_subfuntree(int);
 extern void		sh_subjobcheck(pid_t);
 extern int		sh_subsavefd(int);
 extern void		sh_subtmpfile(void);
-extern void		sh_pwdupdate(int);
-extern int		sh_validate_subpwdfd(void);
 extern char 		*sh_substitute(const char*,const char*,char*);
 extern void		sh_timetraps(void);
 extern const char	*_sh_translate(const char*);
 extern int		sh_trace(char*[],int);
 extern void		sh_trim(char*);
 extern int		sh_type(const char*);
 extern void             sh_unscope(void);
+#if _lib_openat
+    extern int		sh_diropenat(int,const char *);
+    extern void		sh_pwdupdate(int);
+    extern int		sh_validate_subpwdfd(void);
+#endif /* _lib_openat */
 #if SHOPT_NAMESPACE
     extern Namval_t	*sh_fsearch(const char *,int);
 #endif /* SHOPT_NAMESPACE */

src/cmd/ksh93/include/shell.h

@@ -372,7 +372,9 @@ struct Shell_s
 	Sfio_t		**sftable;
 	unsigned char	*fdstatus;
 	char		*pwd;
+#if _lib_openat
 	int		pwdfd;		/* file descriptor for pwd */
+#endif /* _lib_openat */
 	void		*jmpbuffer;
 	void		*mktype;
 	Sfio_t		*strbuf;

src/cmd/ksh93/sh/fault.c

@@ -687,8 +687,10 @@ noreturn void sh_done(int sig)
 	if(sh_isoption(SH_NOEXEC))
 		kiaclose((Lex_t*)sh.lex_context);
 #endif /* SHOPT_KIA */
+#if _lib_openat
 	if(sh.pwdfd > 0)
 		close(sh.pwdfd);
+#endif /* _lib_openat */
 	/* Exit with portable 8-bit status (128 + signum) if last child process exits due to signal */
 	if(sh.chldexitsig)
 		savxit = savxit & ~SH_EXITSIG | 0200;

src/cmd/ksh93/sh/path.c

@@ -249,8 +249,10 @@ char *path_pwd(void)
 	if(!tofree)
 		cp = sh_strdup(cp);
 	sh.pwd = cp;
+#if _lib_openat
 	/* Set sh.pwdfd */
 	sh_pwdupdate(sh_diropenat(AT_FDCWD,cp));
+#endif /* _lib_openat */
 	return sh.pwd;
 }
 

src/cmd/ksh93/sh/subshell.c

@@ -85,6 +85,9 @@ static struct subshell
 	char		rand_state;         /* 0 means sp->rand_seed hasn't been set, 1 is the opposite */
 	uint32_t	srand_upper_bound;  /* parent shell's upper bound for $SRANDOM */
 	int		pwdfd;              /* parent shell's file descriptor for PWD */
+#if !_lib_openat
+	char		pwdclose;
+#endif /* !_lib_openat */
 } *subshell_data;
 
 static unsigned int subenv;
@@ -446,6 +449,8 @@ void sh_subjobcheck(pid_t pid)
 	}
 }
 
+#if _lib_openat
+
 /*
  * Set the file descriptor for the current shell's PWD without wiping
  * out the stored file descriptor for the parent shell's PWD.
@@ -468,6 +473,8 @@ int sh_validate_subpwdfd(void)
 	return sp->pwdfd > 0;
 }
 
+#endif /* _lib_openat */
+
 /*
  * Run command tree <t> in a virtual subshell
  * If comsub is not null, then output will be placed in temp file (or buffer)
@@ -516,6 +523,10 @@ Sfio_t *sh_subshell(Shnode_t *t, volatile int flags, int comsub)
 		path_get(e_dot);
 		sh.pathinit = 0;
 	}
+#if !_lib_openat
+	if(!sh.pwd)
+		path_pwd();
+#endif /* !_lib_openat */
 	sp->bckpid = sh.bckpid;
 	if(comsub)
 		sh_stats(STAT_COMSUB);
@@ -531,8 +542,40 @@ Sfio_t *sh_subshell(Shnode_t *t, volatile int flags, int comsub)
 	if(!sh.subshare)
 	{
 		char *save_debugtrap = 0;
+#if _lib_openat
 		sp->pwd = sh_strdup(sh.pwd);
 		sp->pwdfd = sh.pwdfd;
+#else
+		struct subshell *xp;
+		sp->pwdfd = -1;
+		for(xp=sp->prev; xp; xp=xp->prev)
+		{
+			if(xp->pwdfd>0 && xp->pwd && strcmp(xp->pwd,sh.pwd)==0)
+			{
+				sp->pwdfd = xp->pwdfd;
+				break;
+			}
+		}
+		if(sp->pwdfd<0)
+		{
+			int n = open(e_dot,O_SEARCH);
+			if(n>=0)
+			{
+				sp->pwdfd = n;
+				if(n<10)
+				{
+					sp->pwdfd = sh_fcntl(n,F_DUPFD,10);
+					close(n);
+				}
+				if(sp->pwdfd>0)
+				{
+					fcntl(sp->pwdfd,F_SETFD,FD_CLOEXEC);
+					sp->pwdclose = 1;
+				}
+			}
+		}
+		sp->pwd = (sh.pwd?sh_strdup(sh.pwd):0);
+#endif /* _lib_openat */
 		sp->mask = sh.mask;
 		sh_stats(STAT_SUBSHELL);
 		/* save trap table */
@@ -606,6 +649,10 @@ Sfio_t *sh_subshell(Shnode_t *t, volatile int flags, int comsub)
 		if(sh.savesig < 0)
 		{
 			sh.savesig = 0;
+#if !_lib_openat
+			if(sp->pwdfd < 0 && !sh.subshare)	/* if we couldn't get a file descriptor to our PWD ... */
+				sh_subfork();			/* ...we have to fork, as we cannot fchdir back to it. */
+#endif /* !_lib_openat */
 			/* Virtual subshells are not safe to suspend (^Z, SIGTSTP) in the interactive main shell. */
 			if(sh_isstate(SH_INTERACTIVE))
 			{
@@ -789,6 +836,7 @@ Sfio_t *sh_subshell(Shnode_t *t, volatile int flags, int comsub)
 			free(savsig);
 		}
 		sh.options = sp->options;
+#if _lib_openat
 		if(sh.pwdfd != sp->pwdfd)
 		{
 			/*
@@ -810,6 +858,18 @@ Sfio_t *sh_subshell(Shnode_t *t, volatile int flags, int comsub)
 			if(fatalerror != 2)
 				sh_pwdupdate(sp->pwdfd);
 		}
+#else
+		/* restore the present working directory */
+		if(sp->pwdfd > 0 && fchdir(sp->pwdfd) < 0)
+		{
+			saveerrno = errno;
+			fatalerror = 2;
+		}
+		else if(sp->pwd && strcmp(sp->pwd,sh.pwd))
+			path_newdir(sh.pathlist);
+		if(sp->pwdclose)
+			close(sp->pwdfd);
+#endif /* _lib_openat */
 		free(sh.pwd);
 		sh.pwd = sp->pwd;
 		if(sp->mask!=sh.mask)

src/lib/libast/features/lib

@@ -31,7 +31,7 @@ lib	gethostname,getpagesize,getrlimit,getuniverse
 lib	glob,iswblank,iswctype,killpg,link,localeconv,madvise
 lib	mbtowc,mbrtowc,memalign,memdup
 lib	mkdir,mkfifo,mktemp,mktime
-lib	mount,opendir,pathconf
+lib	mount,opendir,openat,pathconf
 lib	readlink,remove,rename,rewinddir,rmdir,setlocale
 lib	setpgrp,setpgrp2,setreuid,setuid
 lib	socketpair