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Code Issues Releases Wiki Activity

cleanup

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This commit is contained in:
J. Nick Koston
2026-01-06 00:50:43 -10:00
parent b40de61224
commit ffb15b592c
1 changed files with 9 additions and 6 deletions
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15
esphome/components/sha256/sha256.cpp
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@@ -10,23 +10,26 @@ namespace esphome::sha256 {
#if defined(USE_ESP32) || defined(USE_LIBRETINY)
// CRITICAL ESP32-S3 HARDWARE SHA ACCELERATION REQUIREMENTS:
// CRITICAL ESP32-S3 HARDWARE SHA ACCELERATION REQUIREMENTS (IDF 5.5.x):
//
// The ESP32-S3 uses hardware DMA for SHA acceleration. The mbedtls_sha256_context structure contains
// internal state that the DMA engine references. This imposes two critical constraints:
// internal state that the DMA engine references. This imposes three critical constraints:
//
// 1. NO VARIABLE LENGTH ARRAYS (VLAs): VLAs corrupt the stack layout, causing the DMA engine to
// 1. ALIGNMENT: The SHA256 object MUST be declared with `alignas(32)` for proper DMA alignment.
// Without this, the DMA engine may crash with an abort in sha_hal_read_digest().
//
// 2. NO VARIABLE LENGTH ARRAYS (VLAs): VLAs corrupt the stack layout, causing the DMA engine to
// write to incorrect memory locations. This results in null pointer dereferences and crashes.
// ALWAYS use fixed-size arrays (e.g., char buf[65], not char buf[size+1]).
//
// 2. SAME STACK FRAME ONLY: The SHA256 object must be created and used entirely within the same
// 3. SAME STACK FRAME ONLY: The SHA256 object must be created and used entirely within the same
// function. NEVER pass the SHA256 object or HashBase pointer to another function. When the stack
// frame changes (function call/return), the DMA references become invalid and will produce
// truncated hash output (20 bytes instead of 32) or corrupt memory.
//
// CORRECT USAGE:
// void my_function() {
// sha256::SHA256 hasher; // Created locally
// alignas(32) sha256::SHA256 hasher; // Created locally with proper alignment
// hasher.init();
// hasher.add(data, len); // Any size, no chunking needed
// hasher.calculate();
@@ -36,7 +39,7 @@ namespace esphome::sha256 {
//
// INCORRECT USAGE (WILL FAIL ON ESP32-S3):
// void my_function() {
// sha256::SHA256 hasher;
// sha256::SHA256 hasher; // WRONG: Missing alignas(32)
// helper(&hasher); // WRONG: Passed to different stack frame
// }
// void helper(HashBase *h) {