Safer code

Add additional compile-time assertions
Add additional comments to define limitations future maintainers should be aware of.

src/usb/uf2/ghostfat.c

@@ -9,6 +9,7 @@
 #include "bootloader_settings.h"
 #include "bootloader.h"
 
+
 typedef struct {
     uint8_t JumpInstruction[3];
     uint8_t OEMInfo[8];
@@ -59,6 +60,7 @@ struct TextFile {
 
 #define STR0(x) #x
 #define STR(x) STR0(x)
+
 const char infoUf2File[] = //
     "UF2 Bootloader " UF2_VERSION "\r\n"
     "Model: " PRODUCT_NAME "\r\n"
@@ -81,11 +83,20 @@ static struct TextFile const info[] = {
     {.name = "INDEX   HTM", .content = indexFile},
     {.name = "CURRENT UF2"},
 };
-#define NUM_INFO (sizeof(info) / sizeof(info[0]))
+
+// WARNING -- code presumes each non-UF2 file content fits in single sector
+//            Cannot programmatically statically assert .content length
+//            for each element above.
+STATIC_ASSERT(ARRAY_SIZE2(indexFile) < 512);
+
+
+#define NUM_FILES (ARRAY_SIZE2(info))
+#define NUM_DIRENTRIES (NUM_FILES + 1) // Code adds volume label as first root directory entry
+
 
 #define UF2_SIZE           (current_flash_size() * 2)
 #define UF2_SECTORS        (UF2_SIZE / 512)
-#define UF2_FIRST_SECTOR   (NUM_INFO + 1)
+#define UF2_FIRST_SECTOR   (NUM_FILES + 1) // WARNING -- code presumes each non-UF2 file content fits in single sector
 #define UF2_LAST_SECTOR    (UF2_FIRST_SECTOR + UF2_SECTORS - 1)
 
 #define RESERVED_SECTORS   1
@@ -99,7 +110,8 @@ static struct TextFile const info[] = {
 
 // all directory entries must fit in a single sector
 // because otherwise current code overflows buffer
-STATIC_ASSERT(NUM_INFO < (512 / sizeof(DirEntry)));
+STATIC_ASSERT(NUM_DIRENTRIES < (512 / sizeof(DirEntry)));
+// STATIC_ASSERT(NUM_DIRENTRIES < (512 / sizeof(DirEntry)) * ROOT_DIR_SECTORS);
 
 
 static FAT_BootBlock const BootBlock = {
@@ -193,8 +205,8 @@ void read_block(uint32_t block_no, uint8_t *data) {
             sectionIdx -= SECTORS_PER_FAT;
         if (sectionIdx == 0) {
             data[0] = 0xf0;
-            for (int i = 1; i < NUM_INFO * 2 + 4; ++i) {
+            for (int i = 1; i < NUM_FILES * 2 + 4; ++i) {
-                data[i] = 0xff;
+                data[i] = 0xff; // WARNING -- code presumes each non-UF2 file content fits in single sector
             }
         }
         for (int i = 0; i < 256; ++i) {
@@ -209,7 +221,7 @@ void read_block(uint32_t block_no, uint8_t *data) {
             DirEntry *d = (void *)data;
             padded_memcpy(d->name, (char const *) BootBlock.VolumeLabel, 11);
             d->attrs = 0x28;
-            for (int i = 0; i < NUM_INFO; ++i) {
+            for (int i = 0; i < NUM_FILES; ++i) {
                 d++;
                 struct TextFile const *inf = &info[i];
                 d->size = inf->content ? strlen(inf->content) : UF2_SIZE;
@@ -219,10 +231,10 @@ void read_block(uint32_t block_no, uint8_t *data) {
         }
     } else {
         sectionIdx -= START_CLUSTERS;
-        if (sectionIdx < NUM_INFO - 1) {
+        if (sectionIdx < NUM_FILES - 1) {
             memcpy(data, info[sectionIdx].content, strlen(info[sectionIdx].content));
         } else {
-            sectionIdx -= NUM_INFO - 1;
+            sectionIdx -= NUM_FILES - 1;
             uint32_t addr = USER_FLASH_START + sectionIdx * 256;
             if (addr < USER_FLASH_START+FLASH_SIZE) {
                 UF2_Block *bl = (void *)data;

src/usb/uf2/uf2.h

@@ -152,3 +152,147 @@ static inline void check_uf2_handover(uint8_t *buffer, uint32_t blocks_remaining
 #endif
 
 #endif
+
+#ifndef ARRAYSIZE2_H
+#define ARRAYSIZE2_H
+
+#ifndef __has_feature
+    #define __has_feature(x) 0 // Compatibility with non-clang compilers.
+#endif
+
+#if __cplusplus >= 199711L
+    #pragma message "using Ivan J. Johnson's ARRAY_SIZE2"
+
+    // Works on older compilers, even Visual C++ 6....
+    // Created by Ivan J. Johnson, March 06, 2007
+    // See http://drdobbs.com/cpp/197800525?pgno=1
+    //
+    // Pseudocode:
+    // if x is not an array
+    //   issue a compile-time error
+    // else
+    //   use the traditional (non-typesafe) C99 COUNTOF expression
+    //
+    // If the argument is any of:
+    //    object of class type, such as an std::vector
+    //    floating-point type
+    //    function pointer
+    //    pointer-to-member
+    // then the first reinterpret_cast<> is not legal (compiler error)
+    //
+    // The type for check1 is chosen and named to help understand
+    // the cause of the error, because the class name is likely to
+    // appear in the compiler error message.
+    //
+    // If check1 succeeds, then the argument must be one of:
+    //    an integral type
+    //    an enumerated type
+    //    a pointer to an object
+    //    an array
+    //
+    // Check2 expands approximately to sizeof(check_type(x, &x)),
+    // where check_type is an overloaded function.
+    // Because this is purely a compile-time computation,
+    // the function is never really called or even implemented,
+    // but it lets the compiler apply overload resolution,
+    // which allows further type discrimination.
+    // There are three possibilities to consider:
+    //    x is an integral type or enumerated type.
+    //      In this case, neither of the two function overloads
+    //      is a match, resulting in a compiler error.
+    //    x is a pointer to an object.
+    //      In this case, the first argument to check_type()
+    //      is a pointer and the second one is a pointer-to-pointer.
+    //      The best function match is the first overload of check_type,
+    //      the one that returns an incomplete type (Is_pointer).
+    //      However, because Is_pointer is an incomplete type,
+    //      sizeof(Is_pointer) is not a valid expression,
+    //      resulting in a compiler error.
+    //    x is an array.
+    //      In this case, the first argument to check_type()
+    //      is an array and the second is a pointer-to-array.
+    //      A pointer-to-array is *NOT* convertible to a
+    //      pointer-to-pointer, so the first overload of
+    //      check_type() is not a match.
+    //      However, an array IS convertible to a pointer,
+    //      and a pointer-to-array already is a pointer.
+    //      Any pointer is convertible to a void*,
+    //      so the second function overload is a match.
+    //      That overload returns a complete type (Is_array).
+    //      Because it's a complete type,
+    //      sizeof(Is_array) is a valid expression.
+    // Thus, the compiler has EXCLUDED every possible type
+    // except arrays via compilation errors before reaching
+    // the third line.
+    // Moreover, check1 and check2 are reduced to the value zero,
+    // while the third line is the old type-unsafe C-style macro,
+    // now made entirely type-safe.
+    // 
+    // Additional benefits:
+    // The result is itself constexpr
+    // 
+    //
+    #define ARRAY_SIZE2(arr) ( \
+       0 * sizeof(reinterpret_cast<const ::Bad_arg_to_COUNTOF*>(arr)) + /*check1*/ \
+       0 * sizeof(::Bad_arg_to_COUNTOF::check_type((arr), &(arr)))    + /*check2*/ \
+       sizeof(arr) / sizeof((arr)[0])                                   /* eval */ \
+       )
+
+    struct Bad_arg_to_COUNTOF {
+       class Is_pointer; // incomplete
+       class Is_array {};
+       template <typename T>
+       static Is_pointer check_type(const T*, const T* const*);
+       static Is_array check_type(const void*, const void*);
+    };
+
+#elif __cplusplus >= 201103L ||  /* any compiler claiming C++11 support */ \
+    _MSC_VER >= 1900 ||          /* Visual C++ 2015 or higher           */ \
+    __has_feature(cxx_constexpr) /* CLang versions supporting constexp  */
+
+    #pragma message "C++11 version ARRAY_SIZE2"
+
+    namespace detail
+    {
+        template <typename T, std::size_t N>
+        constexpr std::size_t countof(T const (&)[N]) noexcept
+        {
+            return N;
+        }
+    } // namespace detail
+    #define ARRAY_SIZE2(arr) detail::countof(arr)
+
+#elif _MSC_VER // Visual C++ fallback
+
+    #pragma message "using Microsoft Visual C++ intrinsic ARRAY_SIZE2"
+    #define ARRAY_SIZE2(arr) _countof(arr)
+
+#elif __cplusplus >= 199711L && ( /* C++ 98 trick */ \
+    defined(__INTEL_COMPILER) ||                     \
+    defined(__clang__) ||                            \
+    (defined(__GNUC__) && (                          \
+        (__GNUC__ > 4) ||                            \
+        (__GNUC__ == 4 && __GNUC_MINOR__ >= 4)       \
+    )))
+
+    #pragma message "C++98 version ARRAY_SIZE2"
+
+    template <typename T, std::size_t N>
+    char(&_ArraySizeHelperRequiresArray(T(&)[N]))[N];
+    #define ARRAY_SIZE2(x) sizeof(_ArraySizeHelperRequiresArray(x))
+
+#else
+
+    #pragma message "Using type-unsafe version of ARRAY_SIZE2"
+    // This is the worst-case scenario macro.
+    // While it is valid C, it is NOT typesafe.
+    // For example, if the parameter arr is a pointer instead of array,
+    // the compiler will SILENTLY give a (likely) incorrect result. 
+    #define ARRAY_SIZE2(arr) sizeof(arr) / sizeof(arr[0])
+
+#endif
+
+
+#endif // ARRAYSIZE2_H
+
+