[reactos] 12/48: [CMD] Reduce stack memory usage when parsing or echoing commands recursively.

[Hermès Bélusca-Maïto]

https://git.reactos.org/?p=reactos.git;a=commitdiff;h=c93f511241bbe00626817…

commit c93f511241bbe006268178ff8e9e4736dd7c209a
Author:     Hermès Bélusca-Maïto <hermes.belusca-maito(a)reactos.org>
AuthorDate: Sat Jun 6 22:00:13 2020 +0200
Commit:     Hermès Bélusca-Maïto <hermes.belusca-maito(a)reactos.org>
CommitDate: Wed Aug 19 20:35:57 2020 +0200

    [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 | 128 ++++++++++++++++++++++--------------------------
 1 file changed, 59 insertions(+), 69 deletions(-)

diff --git a/base/shell/cmd/parser.c b/base/shell/cmd/parser.c
index 9f4552aa5ad..88787efc7f5 100644
--- a/base/shell/cmd/parser.c
+++ b/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)
-    {
-        FreeCommand(Cmd);
-        ParseError();
-        return NULL;
-    }
+    if (CurrentTokenType != TOK_NORMAL)
+        goto error;
 
     /* 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)
-            {
-                FreeCommand(Cmd);
-                ParseError();
-                return NULL;
-            }
+                goto error;
             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);
-    ParseError();
-    return NULL;
+    goto error;
 
 condition_done:
     Cmd->Subcommands = ParseCommandOp(C_OP_LOWEST);
     if (Cmd->Subcommands == NULL)
-    {
-        FreeCommand(Cmd);
-        return NULL;
-    }
+        goto error;
     if (_tcsicmp(CurrentToken, _T("else")) == 0)
     {
         Cmd->Subcommands->Next = ParseCommandOp(C_OP_LOWEST);
         if (Cmd->Subcommands->Next == NULL)
-        {
-            FreeCommand(Cmd);
-            return NULL;
-        }
+            goto error;
     }
 
     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)
-    {
-        FreeCommand(Cmd);
-        return NULL;
-    }
+        goto error;
 
     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);
-        if (Type == TOK_NORMAL)
+        ParseToken(0, NULL);
+        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))
-            ConOutPrintf(_T("%s"), Buf);
-        if (SubstituteForVars(Cmd->Command.Rest, Buf))
+        if (SubstituteForVars(Cmd->Command.First, TempBuf))
+            ConOutPrintf(_T("%s"), TempBuf);
+        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))
-            ConOutPrintf(_T(" %s"), Buf);
+        if (Cmd->If.LeftArg && SubstituteForVars(Cmd->If.LeftArg,
TempBuf))
+            ConOutPrintf(_T(" %s"), TempBuf);
         ConOutPrintf(_T(" %s"), IfOperatorString[Cmd->If.Operator]);
-        if (SubstituteForVars(Cmd->If.RightArg, Buf))
-            ConOutPrintf(_T(" %s "), Buf);
+        if (SubstituteForVars(Cmd->If.RightArg, TempBuf))
+            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))
-            ConOutPrintf(_T(" %%%c in (%s) do "), Cmd->For.Variable, Buf);
+        if (Cmd->For.List && SubstituteForVars(Cmd->For.List, TempBuf))
+            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;
-        STRING(Buf);
-        if (!SubstituteForVars(Cmd->Command.Rest, Buf)) return NULL;
-        STRING(Buf);
+        if (!SubstituteForVars(Cmd->Command.First, TempBuf)) return NULL;
+        STRING(TempBuf);
+        if (!SubstituteForVars(Cmd->Command.Rest, TempBuf)) return NULL;
+        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))
-            PRINTF(_T(" %s"), Buf);
+        if (Cmd->If.LeftArg && SubstituteForVars(Cmd->If.LeftArg,
TempBuf))
+            PRINTF(_T(" %s"), TempBuf);
         PRINTF(_T(" %s"), IfOperatorString[Cmd->If.Operator]);
-        if (!SubstituteForVars(Cmd->If.RightArg, Buf)) return NULL;
-        PRINTF(_T(" %s "), Buf);
+        if (!SubstituteForVars(Cmd->If.RightArg, TempBuf)) return NULL;
+        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))
-            PRINTF(_T(" %%%c in (%s) do "), Cmd->For.Variable, Buf);
+        if (Cmd->For.List && SubstituteForVars(Cmd->For.List, TempBuf))
+            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;