[CMD] Reduce stack memory usage when parsing or echoing commands recursively.

- Use a common large string buffer for temporary command substitutions/expansions,
  instead of having such a buffer in the local stack of the parsing and
  echoing functions that may be called recursively. Since CMD executes
  synchronously we know that this common buffer can only be used once at
  a time.

- Also do a small code cleanup in ParseIf(), ParseFor() and ParseCommandPart().

base/shell/cmd/parser.c

@@ -57,6 +57,9 @@ enum
     TOK_END_BLOCK
 };
 
+/* Scratch buffer for temporary command substitutions / expansions */
+static TCHAR TempBuf[CMDLINE_LENGTH];
+
 static BOOL bParseError;
 static BOOL bLineContinuations;
 static TCHAR ParseLine[CMDLINE_LENGTH];
@@ -370,7 +373,6 @@ static PARSED_COMMAND *ParseBlock(REDIRECTION *RedirList)
 /* Parse an IF statement */
 static PARSED_COMMAND *ParseIf(void)
 {
-    int Type;
     PARSED_COMMAND *Cmd;
 
     Cmd = cmd_alloc(sizeof(PARSED_COMMAND));
@@ -383,24 +385,19 @@ static PARSED_COMMAND *ParseIf(void)
     memset(Cmd, 0, sizeof(PARSED_COMMAND));
     Cmd->Type = C_IF;
 
-    Type = CurrentTokenType;
     if (_tcsicmp(CurrentToken, _T("/I")) == 0)
     {
         Cmd->If.Flags |= IFFLAG_IGNORECASE;
-        Type = ParseToken(0, STANDARD_SEPS);
+        ParseToken(0, STANDARD_SEPS);
     }
     if (_tcsicmp(CurrentToken, _T("not")) == 0)
     {
         Cmd->If.Flags |= IFFLAG_NEGATE;
-        Type = ParseToken(0, STANDARD_SEPS);
+        ParseToken(0, STANDARD_SEPS);
     }
 
-    if (Type != TOK_NORMAL)
+    if (CurrentTokenType != TOK_NORMAL)
-    {
+        goto error;
-        FreeCommand(Cmd);
-        ParseError();
-        return NULL;
-    }
 
     /* Check for unary operators */
     for (; Cmd->If.Operator <= IF_MAX_UNARY; Cmd->If.Operator++)
@@ -408,11 +405,7 @@ static PARSED_COMMAND *ParseIf(void)
         if (_tcsicmp(CurrentToken, IfOperatorString[Cmd->If.Operator]) == 0)
         {
             if (ParseToken(0, STANDARD_SEPS) != TOK_NORMAL)
-            {
+                goto error;
-                FreeCommand(Cmd);
-                ParseError();
-                return NULL;
-            }
             Cmd->If.RightArg = cmd_dup(CurrentToken);
             goto condition_done;
         }
@@ -435,33 +428,30 @@ static PARSED_COMMAND *ParseIf(void)
         if (_tcsicmp(CurrentToken, IfOperatorString[Cmd->If.Operator]) == 0)
         {
             if (ParseToken(0, STANDARD_SEPS) != TOK_NORMAL)
-                break;
+                goto error;
             Cmd->If.RightArg = cmd_dup(CurrentToken);
             goto condition_done;
         }
     }
-    FreeCommand(Cmd);
+    goto error;
-    ParseError();
-    return NULL;
 
 condition_done:
     Cmd->Subcommands = ParseCommandOp(C_OP_LOWEST);
     if (Cmd->Subcommands == NULL)
-    {
+        goto error;
-        FreeCommand(Cmd);
-        return NULL;
-    }
     if (_tcsicmp(CurrentToken, _T("else")) == 0)
     {
         Cmd->Subcommands->Next = ParseCommandOp(C_OP_LOWEST);
         if (Cmd->Subcommands->Next == NULL)
-        {
+            goto error;
-            FreeCommand(Cmd);
-            return NULL;
-        }
     }
 
     return Cmd;
+
+error:
+    FreeCommand(Cmd);
+    ParseError();
+    return NULL;
 }
 
 /*
@@ -471,7 +461,7 @@ condition_done:
 static PARSED_COMMAND *ParseFor(void)
 {
     PARSED_COMMAND *Cmd;
-    TCHAR List[CMDLINE_LENGTH];
+    TCHAR* List = TempBuf;
     TCHAR *Pos = List;
 
     Cmd = cmd_alloc(sizeof(PARSED_COMMAND));
@@ -487,7 +477,9 @@ static PARSED_COMMAND *ParseFor(void)
     while (1)
     {
         if (_tcsicmp(CurrentToken, _T("/D")) == 0)
+        {
             Cmd->For.Switches |= FOR_DIRS;
+        }
         else if (_tcsicmp(CurrentToken, _T("/F")) == 0)
         {
             Cmd->For.Switches |= FOR_F;
@@ -500,7 +492,9 @@ static PARSED_COMMAND *ParseFor(void)
             }
         }
         else if (_tcsicmp(CurrentToken, _T("/L")) == 0)
+        {
             Cmd->For.Switches |= FOR_LOOP;
+        }
         else if (_tcsicmp(CurrentToken, _T("/R")) == 0)
         {
             Cmd->For.Switches |= FOR_RECURSIVE;
@@ -514,7 +508,10 @@ static PARSED_COMMAND *ParseFor(void)
             }
         }
         else
+        {
             break;
+        }
+
         ParseToken(0, STANDARD_SEPS);
     }
 
@@ -540,24 +537,22 @@ static PARSED_COMMAND *ParseFor(void)
 
     while (1)
     {
-        int Type;
-
         /* Pretend we're inside a block so the tokenizer will stop on ')' */
         InsideBlock++;
-        Type = ParseToken(0, STANDARD_SEPS);
+        ParseToken(0, STANDARD_SEPS);
         InsideBlock--;
 
-        if (Type == TOK_END_BLOCK)
+        if (CurrentTokenType == TOK_END_BLOCK)
             break;
 
-        if (Type == TOK_END)
+        if (CurrentTokenType == TOK_END)
         {
             /* Skip past the \n */
             ParseChar();
             continue;
         }
 
-        if (Type != TOK_NORMAL)
+        if (CurrentTokenType != TOK_NORMAL)
             goto error;
 
         if (Pos != List)
@@ -576,10 +571,7 @@ static PARSED_COMMAND *ParseFor(void)
 
     Cmd->Subcommands = ParseCommandOp(C_OP_LOWEST);
     if (Cmd->Subcommands == NULL)
-    {
+        goto error;
-        FreeCommand(Cmd);
-        return NULL;
-    }
 
     return Cmd;
 
@@ -631,8 +623,8 @@ static DECLSPEC_NOINLINE PARSED_COMMAND *ParseCommandPart(REDIRECTION *RedirList
     /* Now get the tail */
     while (1)
     {
-        int Type = ParseToken(0, NULL);
+        ParseToken(0, NULL);
-        if (Type == TOK_NORMAL)
+        if (CurrentTokenType == TOK_NORMAL)
         {
             if (Pos + _tcslen(CurrentToken) >= &ParsedLine[CMDLINE_LENGTH])
             {
@@ -642,7 +634,7 @@ static DECLSPEC_NOINLINE PARSED_COMMAND *ParseCommandPart(REDIRECTION *RedirList
             }
             Pos = _stpcpy(Pos, CurrentToken);
         }
-        else if (Type == TOK_REDIRECTION)
+        else if (CurrentTokenType == TOK_REDIRECTION)
         {
             if (!ParseRedirection(&RedirList))
                 return NULL;
@@ -1123,7 +1115,6 @@ dump:
 VOID
 EchoCommand(PARSED_COMMAND *Cmd)
 {
-    TCHAR Buf[CMDLINE_LENGTH];
     PARSED_COMMAND *Sub;
     REDIRECTION *Redir;
 
@@ -1131,14 +1122,14 @@ EchoCommand(PARSED_COMMAND *Cmd)
     {
     case C_COMMAND:
     {
-        if (SubstituteForVars(Cmd->Command.First, Buf))
+        if (SubstituteForVars(Cmd->Command.First, TempBuf))
-            ConOutPrintf(_T("%s"), Buf);
+            ConOutPrintf(_T("%s"), TempBuf);
-        if (SubstituteForVars(Cmd->Command.Rest, Buf))
+        if (SubstituteForVars(Cmd->Command.Rest, TempBuf))
         {
-            ConOutPrintf(_T("%s"), Buf);
+            ConOutPrintf(_T("%s"), TempBuf);
 #ifdef MSCMD_ECHO_COMMAND_COMPAT
             /* NOTE: For Windows compatibility, add a trailing space after printing the command parameter, if present */
-            if (*Buf) ConOutChar(_T(' '));
+            if (*TempBuf) ConOutChar(_T(' '));
 #endif
         }
         break;
@@ -1214,11 +1205,11 @@ EchoCommand(PARSED_COMMAND *Cmd)
             ConOutPuts(_T(" /I"));
         if (Cmd->If.Flags & IFFLAG_NEGATE)
             ConOutPuts(_T(" not"));
-        if (Cmd->If.LeftArg && SubstituteForVars(Cmd->If.LeftArg, Buf))
+        if (Cmd->If.LeftArg && SubstituteForVars(Cmd->If.LeftArg, TempBuf))
-            ConOutPrintf(_T(" %s"), Buf);
+            ConOutPrintf(_T(" %s"), TempBuf);
         ConOutPrintf(_T(" %s"), IfOperatorString[Cmd->If.Operator]);
-        if (SubstituteForVars(Cmd->If.RightArg, Buf))
+        if (SubstituteForVars(Cmd->If.RightArg, TempBuf))
-            ConOutPrintf(_T(" %s "), Buf);
+            ConOutPrintf(_T(" %s "), TempBuf);
         Sub = Cmd->Subcommands;
         EchoCommand(Sub);
         if (Sub->Next)
@@ -1238,8 +1229,8 @@ EchoCommand(PARSED_COMMAND *Cmd)
         if (Cmd->For.Switches & FOR_RECURSIVE) ConOutPuts(_T(" /R"));
         if (Cmd->For.Params)
             ConOutPrintf(_T(" %s"), Cmd->For.Params);
-        if (Cmd->For.List && SubstituteForVars(Cmd->For.List, Buf))
+        if (Cmd->For.List && SubstituteForVars(Cmd->For.List, TempBuf))
-            ConOutPrintf(_T(" %%%c in (%s) do "), Cmd->For.Variable, Buf);
+            ConOutPrintf(_T(" %%%c in (%s) do "), Cmd->For.Variable, TempBuf);
         else
             ConOutPrintf(_T(" %%%c in (%s) do "), Cmd->For.Variable, Cmd->For.List);
         EchoCommand(Cmd->Subcommands);
@@ -1253,16 +1244,16 @@ EchoCommand(PARSED_COMMAND *Cmd)
 
     for (Redir = Cmd->Redirections; Redir; Redir = Redir->Next)
     {
-        if (SubstituteForVars(Redir->Filename, Buf))
+        if (SubstituteForVars(Redir->Filename, TempBuf))
         {
 #ifdef MSCMD_ECHO_COMMAND_COMPAT
             ConOutPrintf(_T("%c%s%s "),
                          _T('0') + Redir->Number,
-                         RedirString[Redir->Mode], Buf);
+                         RedirString[Redir->Mode], TempBuf);
 #else
             ConOutPrintf(_T(" %c%s%s"),
                          _T('0') + Redir->Number,
-                         RedirString[Redir->Mode], Buf);
+                         RedirString[Redir->Mode], TempBuf);
 #endif
         }
     }
@@ -1276,7 +1267,6 @@ EchoCommand(PARSED_COMMAND *Cmd)
 TCHAR *
 Unparse(PARSED_COMMAND *Cmd, TCHAR *Out, TCHAR *OutEnd)
 {
-    TCHAR Buf[CMDLINE_LENGTH];
     PARSED_COMMAND *Sub;
     REDIRECTION *Redir;
 
@@ -1313,10 +1303,10 @@ do { \
         /* This is fragile since there could be special characters, but
          * Windows doesn't bother escaping them, so for compatibility
          * we probably shouldn't do it either */
-        if (!SubstituteForVars(Cmd->Command.First, Buf)) return NULL;
+        if (!SubstituteForVars(Cmd->Command.First, TempBuf)) return NULL;
-        STRING(Buf);
+        STRING(TempBuf);
-        if (!SubstituteForVars(Cmd->Command.Rest, Buf)) return NULL;
+        if (!SubstituteForVars(Cmd->Command.Rest, TempBuf)) return NULL;
-        STRING(Buf);
+        STRING(TempBuf);
         break;
 
     case C_QUIET:
@@ -1351,11 +1341,11 @@ do { \
             STRING(_T(" /I"));
         if (Cmd->If.Flags & IFFLAG_NEGATE)
             STRING(_T(" not"));
-        if (Cmd->If.LeftArg && SubstituteForVars(Cmd->If.LeftArg, Buf))
+        if (Cmd->If.LeftArg && SubstituteForVars(Cmd->If.LeftArg, TempBuf))
-            PRINTF(_T(" %s"), Buf);
+            PRINTF(_T(" %s"), TempBuf);
         PRINTF(_T(" %s"), IfOperatorString[Cmd->If.Operator]);
-        if (!SubstituteForVars(Cmd->If.RightArg, Buf)) return NULL;
+        if (!SubstituteForVars(Cmd->If.RightArg, TempBuf)) return NULL;
-        PRINTF(_T(" %s "), Buf);
+        PRINTF(_T(" %s "), TempBuf);
         Sub = Cmd->Subcommands;
         RECURSE(Sub);
         if (Sub->Next)
@@ -1373,8 +1363,8 @@ do { \
         if (Cmd->For.Switches & FOR_RECURSIVE) STRING(_T(" /R"));
         if (Cmd->For.Params)
             PRINTF(_T(" %s"), Cmd->For.Params);
-        if (Cmd->For.List && SubstituteForVars(Cmd->For.List, Buf))
+        if (Cmd->For.List && SubstituteForVars(Cmd->For.List, TempBuf))
-            PRINTF(_T(" %%%c in (%s) do "), Cmd->For.Variable, Buf);
+            PRINTF(_T(" %%%c in (%s) do "), Cmd->For.Variable, TempBuf);
         else
             PRINTF(_T(" %%%c in (%s) do "), Cmd->For.Variable, Cmd->For.List);
         RECURSE(Cmd->Subcommands);
@@ -1387,10 +1377,10 @@ do { \
 
     for (Redir = Cmd->Redirections; Redir; Redir = Redir->Next)
     {
-        if (!SubstituteForVars(Redir->Filename, Buf))
+        if (!SubstituteForVars(Redir->Filename, TempBuf))
             return NULL;
         PRINTF(_T(" %c%s%s"), _T('0') + Redir->Number,
-               RedirString[Redir->Mode], Buf);
+               RedirString[Redir->Mode], TempBuf);
     }
     return Out;