The length of the src area is calculated wrongly in the memccpy replace function. This causes a false positive overlap warning when the c character is found early in the src memory area. Fix this by making sure the srclen is calculated correctly (only covers the area of bytes actually copied). And add a new testcase in memcheck/tests/memccpy2.c that fails (shows a false positive) with the old implementation, but passes with the new  implementation of the memccpy replacement function.

diff --git a/memcheck/tests/memccpy2.c b/memcheck/tests/memccpy2.c
index a5a1dfc9f0af..4a54e04c0ae6 100644
--- a/memcheck/tests/memccpy2.c
+++ b/memcheck/tests/memccpy2.c
@@ -9,5 +9,7 @@ int main(void)
    memccpy(astring+10, astring, '#', len-10);
    sprintf(astring, "this is a string # with something to seek");
    memccpy(astring, astring+10, '#', len);
+   sprintf(astring, "this is a string # with something to seek");
+   memccpy(astring+10, astring, ' ', len-10); /* space is early, no overlap */
 }
 
diff --git a/shared/vg_replace_strmem.c b/shared/vg_replace_strmem.c
index 737abbf67898..036763efcf0c 100644
--- a/shared/vg_replace_strmem.c
+++ b/shared/vg_replace_strmem.c
@@ -2364,9 +2364,9 @@ static inline void my_exit ( int x )
       \
       while (i-- > 0) \
          if ((*d++ = *s++) == x) { \
-            SizeT srclen = (i < len) ? i : len; \
+            SizeT srclen = (i < len) ? len - i : len; \
             RECORD_COPY(srclen); \
-            if (is_overlap(dst, src, srclen, srclen)) \
+            if (is_overlap(dst, src, len, srclen)) \
                RECORD_OVERLAP_ERROR("memccpy", dst, src, len); \
             return d; \
          } \