Fix "out of bounds" undefined behavior

vitalybuka · vitalybuka · commit 676a2571ba6f · 2020-04-01T00:55:35.000-07:00
This is detected with clang and -fsanitizer=bounds.

Out-of-bound addressing array of fixed size is undefined
behavior in both C and C++. It is so even if underlying
memory is properly allocated.

Easy fix here is to iterate with this pointer instead of
pixel_type::c array.
diff --git a/extern/agg24-svn/include/agg_pixfmt_rgba.h b/extern/agg24-svn/include/agg_pixfmt_rgba.h
@@ -1515,13 +1515,12 @@ namespace agg
         typedef typename color_type::calc_type calc_type;
         enum 
         {
-            num_components = 4,
             pix_step = 4,
             pix_width = sizeof(value_type) * pix_step,
         };
         struct pixel_type
         {
-            value_type c[num_components];
+            value_type c[pix_step];
 
             void set(value_type r, value_type g, value_type b, value_type a)
             {
@@ -1555,22 +1554,22 @@ namespace agg
 
             pixel_type* next()
             {
-                return (pixel_type*)(c + pix_step);
+                return this + 1;
             }
 
             const pixel_type* next() const
             {
-                return (const pixel_type*)(c + pix_step);
+                return this + 1;
             }
 
             pixel_type* advance(int n)
             {
-                return (pixel_type*)(c + n * pix_step);
+                return this + n;
             }
 
             const pixel_type* advance(int n) const
             {
-                return (const pixel_type*)(c + n * pix_step);
+                return this + n;
             }
         };
 
@@ -2193,13 +2192,12 @@ namespace agg
         typedef typename color_type::calc_type calc_type;
         enum 
         {
-            num_components = 4,
             pix_step = 4,
             pix_width  = sizeof(value_type) * pix_step,
         };
         struct pixel_type
         {
-            value_type c[num_components];
+            value_type c[pix_step];
 
             void set(value_type r, value_type g, value_type b, value_type a)
             {
@@ -2233,22 +2231,22 @@ namespace agg
 
             pixel_type* next()
             {
-                return (pixel_type*)(c + pix_step);
+                return this + 1;
             }
 
             const pixel_type* next() const
             {
-                return (const pixel_type*)(c + pix_step);
+                return this + 1;
             }
 
             pixel_type* advance(int n)
             {
-                return (pixel_type*)(c + n * pix_step);
+                return this + n;
             }
 
             const pixel_type* advance(int n) const
             {
-                return (const pixel_type*)(c + n * pix_step);
+                return this + n;
             }
         };
 

Original file line number	Diff line number	Diff line change
`@@ -1515,13 +1515,12 @@ namespace agg`
`1515`	`1515`	`typedef typename color_type::calc_type calc_type;`
`1516`	`1516`	`enum`
`1517`	`1517`	`{`
`1518`		`- num_components = 4,`
`1519`	`1518`	`pix_step = 4,`
`1520`	`1519`	`pix_width = sizeof(value_type) * pix_step,`
`1521`	`1520`	`};`
`1522`	`1521`	`struct pixel_type`
`1523`	`1522`	`{`
`1524`		`- value_type c[num_components];`
	`1523`	`+ value_type c[pix_step];`
`1525`	`1524`
`1526`	`1525`	`void set(value_type r, value_type g, value_type b, value_type a)`
`1527`	`1526`	`{`
`@@ -1555,22 +1554,22 @@ namespace agg`
`1555`	`1554`
`1556`	`1555`	`pixel_type* next()`
`1557`	`1556`	`{`
`1558`		`- return (pixel_type*)(c + pix_step);`
	`1557`	`+ return this + 1;`
`1559`	`1558`	`}`
`1560`	`1559`
`1561`	`1560`	`const pixel_type* next() const`
`1562`	`1561`	`{`
`1563`		`- return (const pixel_type*)(c + pix_step);`
	`1562`	`+ return this + 1;`
`1564`	`1563`	`}`
`1565`	`1564`
`1566`	`1565`	`pixel_type* advance(int n)`
`1567`	`1566`	`{`
`1568`		`- return (pixel_type)(c + n pix_step);`
	`1567`	`+ return this + n;`
`1569`	`1568`	`}`
`1570`	`1569`
`1571`	`1570`	`const pixel_type* advance(int n) const`
`1572`	`1571`	`{`
`1573`		`- return (const pixel_type)(c + n pix_step);`
	`1572`	`+ return this + n;`
`1574`	`1573`	`}`
`1575`	`1574`	`};`
`1576`	`1575`
`@@ -2193,13 +2192,12 @@ namespace agg`
`2193`	`2192`	`typedef typename color_type::calc_type calc_type;`
`2194`	`2193`	`enum`
`2195`	`2194`	`{`
`2196`		`- num_components = 4,`
`2197`	`2195`	`pix_step = 4,`
`2198`	`2196`	`pix_width = sizeof(value_type) * pix_step,`
`2199`	`2197`	`};`
`2200`	`2198`	`struct pixel_type`
`2201`	`2199`	`{`
`2202`		`- value_type c[num_components];`
	`2200`	`+ value_type c[pix_step];`
`2203`	`2201`
`2204`	`2202`	`void set(value_type r, value_type g, value_type b, value_type a)`
`2205`	`2203`	`{`
`@@ -2233,22 +2231,22 @@ namespace agg`
`2233`	`2231`
`2234`	`2232`	`pixel_type* next()`
`2235`	`2233`	`{`
`2236`		`- return (pixel_type*)(c + pix_step);`
	`2234`	`+ return this + 1;`
`2237`	`2235`	`}`
`2238`	`2236`
`2239`	`2237`	`const pixel_type* next() const`
`2240`	`2238`	`{`
`2241`		`- return (const pixel_type*)(c + pix_step);`
	`2239`	`+ return this + 1;`
`2242`	`2240`	`}`
`2243`	`2241`
`2244`	`2242`	`pixel_type* advance(int n)`
`2245`	`2243`	`{`
`2246`		`- return (pixel_type)(c + n pix_step);`
	`2244`	`+ return this + n;`
`2247`	`2245`	`}`
`2248`	`2246`
`2249`	`2247`	`const pixel_type* advance(int n) const`
`2250`	`2248`	`{`
`2251`		`- return (const pixel_type)(c + n pix_step);`
	`2249`	`+ return this + n;`
`2252`	`2250`	`}`
`2253`	`2251`	`};`
`2254`	`2252`