command -x: tweak args list size detection (re: 9ddb45b1)

src/cmd/ksh93/features/externs: ARG_EXTRA_BYTES detection:
- Improve detection of extra bytes per argument: on every loop
  iteration, recalculate the size of the environment while taking
  the amount extra bytes we're currently trying into account. Also
  count arguments (argv[]) as they are stored in the same buffer.
  On 64-bit Linux with glibc, this now detects 9 extra bytes per
  argument instead of 8. An odd number (literally and figuratively)
  but apparently it needs it; I do think my method is correct now.
  On 64-bit Solaris and macOS, this still detects 8 extra bytes.
  (On 64-bit Linux with musl C library, it detects 0 bytes. Nice.)

src/cmd/ksh93/sh/path.c: path_xargs():
- Remove the kludge subtracting twice the size of the environment.
  With the feature test fixed, this should no longer fail on Linux.
- Take into account the size of the final null element in the
  argument and environment lists.

src/cmd/ksh93/tests/path.sh:
- Do not use awk for the test due to breakage in the system awks
  on Solaris/Illumos (hangs) and AIX & UnixWare (drops arguments).
  Instead, use (wait for it...) ksh. It's a bit slower, but works.

src/cmd/ksh93/features/externs

@@ -17,8 +17,8 @@ tst	note{ determining extra bytes per argument for arguments list }end output{
 	 * Figure out if this OS requires extra bytes per argument
 	 * in the arguments list of a process.
 	 * Outputs an appropriate #define ARG_EXTRA_BYTES.
-	 * Without this, 'command -x' failed with E2BIG on macOS and Linux even
+	 * Without this, 'command -x' failed with E2BIG on macOS, Linux and Solaris
-	 * if all the arguments should fit in ARG_MAX based on their length.
+	 * even if all the arguments should fit in ARG_MAX based on their length.
 	 */
 
 	/* AST includes */
@@ -43,20 +43,25 @@ tst	note{ determining extra bytes per argument for arguments list }end output{
 
 	int main(int argc,char *argv[])
 	{
-		int extra_bytes = 0, envlen = 0, argmax, i;
+		int extra_bytes = 0, envlen, argmax, i;
 		pid_t childpid;
 
 		error_info.id="ARG_EXTRA_BYTES test (parent)";
-		for(i=0; environ[i]; i++)
-			envlen += strlen(environ[i]) + 1;
-		argmax = strtoimax(astconf("ARG_MAX",NiL,NiL),NiL,0) - 2 * envlen;
-		if (argmax < 2048)
-		{
-			error(ERROR_ERROR|2, "argmax too small");
-			return 1;
-		}
 		while(1)
 		{
+			envlen = 0;
+			for(i=0; argv[i]; i++)
+				envlen += strlen(argv[i]) + 1 + extra_bytes;
+			envlen += 1 + extra_bytes;	/* final null element */
+			for(i=0; environ[i]; i++)
+				envlen += strlen(environ[i]) + 1 + extra_bytes;
+			envlen += 1 + extra_bytes;	/* final null element */
+			argmax = strtoimax(astconf("ARG_MAX",NiL,NiL),NiL,0) - envlen;
+			if (argmax < 2048)
+			{
+				error(ERROR_ERROR|2, "argmax too small");
+				return 1;
+			}
 			if(!(childpid = fork()))
 			{
 				/* child */
@@ -122,5 +127,5 @@ tst	note{ determining extra bytes per argument for arguments list }end output{
 		return 0;
 	}
 }end fail{
-	echo "#define ARG_EXTRA_BYTES	8	/* BUG: test failed; assuming 8 */"
+	echo "#define ARG_EXTRA_BYTES	16	/* BUG: test failed; assuming 16 */"
 }end

src/cmd/ksh93/sh/path.c

@@ -164,11 +164,12 @@ static pid_t path_xargs(Shell_t *shp,const char *path, char *argv[],char *const
 		return((pid_t)-1);
 	size = shp->gd->lim.arg_max - (ARG_EXTRA_BYTES > 2 ? 1024*ARG_EXTRA_BYTES : 2048);
 	for(ev=envp; cp= *ev; ev++)
-		size -= 2 * (strlen(cp) + 1 + ARG_EXTRA_BYTES);
+		size -= strlen(cp) + 1 + ARG_EXTRA_BYTES;
 	for(av=argv; (cp= *av) && av< &argv[shp->xargmin]; av++)  
 		size -= strlen(cp) + 1 + ARG_EXTRA_BYTES;
 	for(av=avlast; cp= *av; av++,nlast++)  
 		size -= strlen(cp) + 1 + ARG_EXTRA_BYTES;
+	size -= 2 + 2 * ARG_EXTRA_BYTES;  /* final null env and arg elements */
 	av =  &argv[shp->xargmin];
 	if(!spawn)
 		job_clear();

src/cmd/ksh93/tests/path.sh

@@ -542,7 +542,7 @@ fi
 ofile=$tmp/command_x_chunks.sh
 trap 'sleep_pid=; while kill -9 $pid; do :; done 2>/dev/null; err_exit "'\''command -x'\'' hung"' TERM
 trap 'kill $sleep_pid; while kill -9 $pid; do :; done 2>/dev/null; trap - INT; kill -s INT $$"' INT
-{ sleep 15; kill $$; } &
+{ sleep 60; kill $$; } &
 sleep_pid=$!
 (
 	export LC_ALL=C
@@ -558,14 +558,17 @@ sleep_pid=$!
 	done
 	print "chunks=0 expargs=$# args=0 expsize=$((${#args}+1)) size=0"
 	unset args
-	command -px awk 'BEGIN {
+	command -x "$SHELL" -c '
-		ARGC -= 2;  # final static args
+		integer i size=0 numargs=${#}-2
-		for (i=1; i<ARGC; i++)
+		for ((i=numargs; i; i--))
-			size += length(ARGV[i]) + 1;
+		do	let "size += ${#1} + 1"
-		print ("let chunks++ args+=")(ARGC - 1)(" size+=")(size);
+			shift
-		if(ARGV[ARGC] != "static_arg_1" || ARGV[ARGC+1] != "final_static_arg_2")
+		done
-			print "err_exit \"'\''command -x'\'': static final arguments for chunk $chunks incorrect\"";
+		print "let chunks++ args+=$numargs size+=$size"
-	}' "$@" static_arg_1 final_static_arg_2
+		if	[[ $0 != static_argzero || $1 != final_static_arg_1 || $2 != final_static_arg_2 ]]
+		then	print "err_exit \"'\''command -x'\'': static arguments for chunk \$chunks incorrect\""
+		fi
+	' static_argzero "$@" final_static_arg_1 final_static_arg_2
 ) >$ofile &
 pid=$!
 wait $pid