ui-ssdiff: move LCS table away from the stack

Printing deferred line changes for files containing long lines would
cause a segfault.

- limit LCS table size: 128x128.
- move LCS table to global context: avoid allocating/freeing memory
  for every deferred line change.

Signed-off-by: Jamie Couture <jamie.couture@gmail.com>

diff --git a/ui-ssdiff.c b/ui-ssdiff.c
index 2481585fb619966173fcde2e4d35ba1614482093..9fb5b1139af12c05d9817d9fcef884b843d928ca 100644 (file)
--- a/ui-ssdiff.c
+++ b/ui-ssdiff.c
@@ -2,10 +2,12 @@
 #include "html.h"
 #include "ui-shared.h"
 #include "ui-diff.h"
+#include "ui-ssdiff.h"
 
 extern int use_ssdiff;
 
 static int current_old_line, current_new_line;
+static int **L = NULL;
 
 struct deferred_lines {
        int line_no;
@@ -16,16 +18,42 @@ struct deferred_lines {
 static struct deferred_lines *deferred_old, *deferred_old_last;
 static struct deferred_lines *deferred_new, *deferred_new_last;
 
+static void create_or_reset_lcs_table()
+{
+       int i;
+
+       if (L != NULL) {
+               memset(*L, 0, sizeof(*L) * MAX_SSDIFF_SIZE);
+               return;
+       }
+
+       // xcalloc will die if we ran out of memory;
+       // not very helpful for debugging
+       L = (int**)xcalloc(MAX_SSDIFF_M, sizeof(int *));
+       *L = (int*)xcalloc(MAX_SSDIFF_SIZE, sizeof(int));
+
+       for (i = 1; i < MAX_SSDIFF_M; i++) {
+               L[i] = *L + i * MAX_SSDIFF_N;
+       }
+}
+
 static char *longest_common_subsequence(char *A, char *B)
 {
        int i, j, ri;
        int m = strlen(A);
        int n = strlen(B);
-       int L[m + 1][n + 1];
-       int tmp1, tmp2;
+       int tmp1, tmp2, length;
        int lcs_length;
        char *result;
 
+       length = (m + 1) * (n + 1);
+
+       // We bail if the lines are too long
+       if (length > MAX_SSDIFF_SIZE)
+               return NULL;
+
+       create_or_reset_lcs_table();
+
        for (i = m; i >= 0; i--) {
                for (j = n; j >= 0; j--) {
                        if (A[i] == '\0' || B[j] == '\0') {
@@ -59,6 +87,7 @@ static char *longest_common_subsequence(char *A, char *B)
                        j += 1;
                }
        }
+
        return result;
 }
 

diff --git a/ui-ssdiff.h b/ui-ssdiff.h
index 64b4b1215adced788d2145cf9b771ed9d669d464..88627e297c8b2091919e6274010d2bb7812ca067 100644 (file)
--- a/ui-ssdiff.h
+++ b/ui-ssdiff.h
@@ -1,6 +1,18 @@
 #ifndef UI_SSDIFF_H
 #define UI_SSDIFF_H
 
+/*
+ * ssdiff line limits
+ */
+#ifndef MAX_SSDIFF_M
+#define MAX_SSDIFF_M 128
+#endif
+
+#ifndef MAX_SSDIFF_N
+#define MAX_SSDIFF_N 128
+#endif
+#define MAX_SSDIFF_SIZE ((MAX_SSDIFF_M) * (MAX_SSDIFF_N))
+
 extern void cgit_ssdiff_print_deferred_lines();
 
 extern void cgit_ssdiff_line_cb(char *line, int len);