lineedit: allocate matchBuf only temporarily: saves MAX_LINELEN bytes

function                                             old     new   delta
input_tab                                           1027    1041     +14
build_match_prefix                                   590     562     -28
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 1/1 up/down: 14/-28)            Total: -14 bytes

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>

1 files changed, 48 insertions, 45 deletions

diff --git a/libbb/lineedit.c b/libbb/lineedit.c
index ff5d28408..a917c5f92 100644
--- a/libbb/lineedit.c
+++ b/libbb/lineedit.c
@@ -150,11 +150,6 @@ struct lineedit_statics {
 #if ENABLE_FEATURE_EDITING_ASK_TERMINAL
         smallint sent_ESC_br6n;
 #endif
-
-        /* Formerly these were big buffers on stack: */
-#if ENABLE_FEATURE_TAB_COMPLETION
-        char input_tab__matchBuf[MAX_LINELEN];
-#endif
 };
 
 /* See lineedit_ptr_hack.c */
@@ -810,17 +805,17 @@ static NOINLINE unsigned complete_cmd_dir_file(const char *command, int type)
 }
 
 /* build_match_prefix:
- * On entry, matchBuf contains everything up to cursor at the moment <tab>
+ * On entry, match_buf contains everything up to cursor at the moment <tab>
  * was pressed. This function looks at it, figures out what part of it
  * constitutes the command/file/directory prefix to use for completion,
- * and rewrites matchBuf to contain only that part.
+ * and rewrites match_buf to contain only that part.
  */
+#define dbg_bmp 0
 /* Helpers: */
 /* QUOT is used on elements of int_buf[], which are bytes,
  * not Unicode chars. Therefore it works correctly even in Unicode mode.
  */
 #define QUOT (UCHAR_MAX+1)
-#define dbg_bmp 0
 static void remove_chunk(int16_t *int_buf, int beg, int end)
 {
         /* beg must be <= end */
@@ -837,25 +832,29 @@ static void remove_chunk(int16_t *int_buf, int beg, int end)
                 bb_putchar('\n');
         }
 }
-static NOINLINE int build_match_prefix(char *matchBuf)
+/* Caller ensures that match_buf points to a malloced buffer
+ * big enough to hold strlen(match_buf)*2 + 2
+ */
+static NOINLINE int build_match_prefix(char *match_buf)
 {
         int i, j;
         int command_mode;
-        int16_t *int_buf;
+        int16_t *int_buf = (int16_t*)match_buf;
 
-        if (dbg_bmp) printf("\n%s\n", matchBuf);
+        if (dbg_bmp) printf("\n%s\n", match_buf);
 
-        int_buf = xmalloc(sizeof(int_buf[0]) * (strlen(matchBuf) + 1));
-        i = 0;
-        while ((int_buf[i] = (unsigned char)matchBuf[i]) != '\0')
-                i++;
+        /* Copy in reverse order, since they overlap */
+        i = strlen(match_buf);
+        do {
+                int_buf[i] = (unsigned char)match_buf[i];
+                i--;
+        } while (i >= 0);
 
         /* Mark every \c as "quoted c" */
-        for (i = j = 0; matchBuf[i]; i++, j++) {
-                if (matchBuf[i] == '\\') {
-                        remove_chunk(int_buf, j, j + 1);
-                        int_buf[j] |= QUOT;
-                        i++;
+        for (i = 0; int_buf[i]; i++) {
+                if (int_buf[i] == '\\') {
+                        remove_chunk(int_buf, i, i + 1);
+                        int_buf[i] |= QUOT;
                 }
         }
         /* Quote-mark "chars" and 'chars', drop delimiters */
@@ -964,13 +963,12 @@ static NOINLINE int build_match_prefix(char *matchBuf)
                 }
         }
 
-        /* Store only match prefix */
+        /* Convert back to string of _chars_ */
         i = 0;
-        while ((matchBuf[i] = int_buf[i]) != '\0')
+        while ((match_buf[i] = int_buf[i]) != '\0')
                 i++;
-        free(int_buf);
 
-        if (dbg_bmp) printf("final matchBuf:'%s'\n", matchBuf);
+        if (dbg_bmp) printf("final match_buf:'%s'\n", match_buf);
 
         return command_mode;
 }
@@ -1037,9 +1035,8 @@ static char *add_quote_for_spec_chars(char *found)
 static NOINLINE void input_tab(smallint *lastWasTab)
 {
         char *chosen_match;
+        char *match_buf;
         size_t len_found;
-/*      char matchBuf[MAX_LINELEN]; */
-#define matchBuf (S.input_tab__matchBuf)
         /* Length of string used for matching */
         unsigned match_pfx_len = match_pfx_len;
         int find_type;
@@ -1065,21 +1062,26 @@ static NOINLINE void input_tab(smallint *lastWasTab)
         }
 
         *lastWasTab = 1;
+        chosen_match = NULL;
 
-        /* Make a local copy of the string --
-         * up to the position of the cursor */
+        /* Make a local copy of the string up to the position of the cursor.
+         * build_match_prefix will expand it into int16_t's, need to allocate
+         * twice as much as the string_len+1.
+         * (we then also (ab)use this extra space later - see (**))
+         */
+        match_buf = xmalloc(MAX_LINELEN * sizeof(int16_t));
 #if !ENABLE_UNICODE_SUPPORT
-        save_string(matchBuf, cursor + 1);
+        save_string(match_buf, cursor + 1); /* +1 for NUL */
 #else
         {
                 CHAR_T wc = command_ps[cursor];
                 command_ps[cursor] = BB_NUL;
-                save_string(matchBuf, MAX_LINELEN);
+                save_string(match_buf, MAX_LINELEN);
                 command_ps[cursor] = wc;
-                cursor_mb = strlen(matchBuf);
+                cursor_mb = strlen(match_buf);
         }
 #endif
-        find_type = build_match_prefix(matchBuf);
+        find_type = build_match_prefix(match_buf);
 
         /* Free up any memory already allocated */
         free_tab_completion_data();
@@ -1088,12 +1090,12 @@ static NOINLINE void input_tab(smallint *lastWasTab)
         /* If the word starts with `~' and there is no slash in the word,
          * then try completing this word as a username. */
         if (state->flags & USERNAME_COMPLETION)
-                if (matchBuf[0] == '~' && strchr(matchBuf, '/') == NULL)
-                        match_pfx_len = complete_username(matchBuf);
+                if (match_buf[0] == '~' && strchr(match_buf, '/') == NULL)
+                        match_pfx_len = complete_username(match_buf);
 #endif
         /* Try to match a command in $PATH, or a directory, or a file */
         if (!matches)
-                match_pfx_len = complete_cmd_dir_file(matchBuf, find_type);
+                match_pfx_len = complete_cmd_dir_file(match_buf, find_type);
         /* Remove duplicates */
         if (matches) {
                 unsigned i;
@@ -1117,7 +1119,7 @@ static NOINLINE void input_tab(smallint *lastWasTab)
                 char *cp;
                 beep();
                 if (!matches)
-                        return; /* no matches at all */
+                        goto ret; /* no matches at all */
                 /* Find common prefix */
                 chosen_match = xstrdup(matches[0]);
                 for (cp = chosen_match; *cp; cp++) {
@@ -1130,8 +1132,7 @@ static NOINLINE void input_tab(smallint *lastWasTab)
                 }
  stop:
                 if (cp == chosen_match) { /* have unique prefix? */
-                        free(chosen_match); /* no */
-                        return;
+                        goto ret; /* no */
                 }
                 *cp = '\0';
                 cp = add_quote_for_spec_chars(chosen_match);
@@ -1158,9 +1159,9 @@ static NOINLINE void input_tab(smallint *lastWasTab)
         if ((int)(len_found - match_pfx_len + command_len) < S.maxsize) {
                 int pos;
                 /* save tail */
-                strcpy(matchBuf, &command_ps[cursor]);
+                strcpy(match_buf, &command_ps[cursor]);
                 /* add match and tail */
-                sprintf(&command_ps[cursor], "%s%s", chosen_match + match_pfx_len, matchBuf);
+                sprintf(&command_ps[cursor], "%s%s", chosen_match + match_pfx_len, match_buf);
                 command_len = strlen(command_ps);
                 /* new pos */
                 pos = cursor + len_found - match_pfx_len;
@@ -1169,19 +1170,20 @@ static NOINLINE void input_tab(smallint *lastWasTab)
         }
 #else
         {
-                char command[MAX_LINELEN];
-                int len = save_string(command, sizeof(command));
+                /* Use 2nd half of match_buf as scratch space - see (**) */
+                char *command = match_buf + MAX_LINELEN;
+                int len = save_string(command, MAX_LINELEN);
                 /* Have space to place the match? */
                 /* cursor_mb + (len_found - match_pfx_len) + (len - cursor_mb) */
                 if ((int)(len_found - match_pfx_len + len) < MAX_LINELEN) {
                         int pos;
                         /* save tail */
-                        strcpy(matchBuf, &command[cursor_mb]);
+                        strcpy(match_buf, &command[cursor_mb]);
                         /* where do we want to have cursor after all? */
                         strcpy(&command[cursor_mb], chosen_match + match_pfx_len);
                         len = load_string(command, S.maxsize);
                         /* add match and tail */
-                        sprintf(&command[cursor_mb], "%s%s", chosen_match + match_pfx_len, matchBuf);
+                        sprintf(&command[cursor_mb], "%s%s", chosen_match + match_pfx_len, match_buf);
                         command_len = load_string(command, S.maxsize);
                         /* write out the matched command */
                         /* paranoia: load_string can return 0 on conv error,
@@ -1191,8 +1193,9 @@ static NOINLINE void input_tab(smallint *lastWasTab)
                 }
         }
 #endif
+ ret:
         free(chosen_match);
-#undef matchBuf
+        free(match_buf);
 }
 
 #endif  /* FEATURE_TAB_COMPLETION */