app_update: fix incorrect first byte from esp_ota_get_app_elf_sha256
At -O2 optimization level, GCC seems to optimize out the copying of the
first byte of the checksum, assuming it is zero. This "miscompilation"
happens because the esp_app_desc struct is declared const, but then modified
post-compilation. Casting to volatile disables the optimization.
Closes:
@@ -89,7 +89,10 @@ int IRAM_ATTR esp_ota_get_app_elf_sha256(char* dst, size_t size)
static bool first_call = true;
if (first_call) {
first_call = false;
- const uint8_t* src = esp_app_desc.app_elf_sha256;
+ // At -O2 optimization level, GCC optimizes out the copying of the first byte of the app_elf_sha256,
+ // because it is zero at compile time, and only modified afterwards by esptool.
+ // Casting to volatile disables the optimization.
+ const volatile uint8_t* src = (const volatile uint8_t*)esp_app_desc.app_elf_sha256;
for (size_t i = 0; i < sizeof(s_app_elf_sha256); ++i) {
s_app_elf_sha256[i] = src[i];
}
