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app_update: fix incorrect first byte from esp_ota_get_app_elf_sha256

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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: https://github.com/espressif/esp-idf/pull/6389
This commit is contained in:
Itay Perl 2021-01-13 02:01:52 +02:00 committed by bot
parent 1e36383909
commit 881909ecda
1 changed files with 4 additions and 1 deletions
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5
components/app_update/esp_app_desc.c
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@ -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];
}