tree-wide: use alignas() for alignment

- Use of `__attribute__((aligned(<NUM>)))` is a compiler extension. We can just use `alignas()`, which is part of the C standard since C11 - Use of `_Alignas()` is a keyword since C11 and `alignas()` the alias provided by `<stdalign.h>`. But `_Alignas()` is deprecated since C23. Let's just go for `alignas()` instead.
RIOT-OS · maribu · Jan 21, 2025 · Jan 21, 2025 · 534a2d2ec8ab53e2a893b1571deccac5c71fc868
commit 534a2d2ec8ab53e2a893b1571deccac5c71fc868
diff --git a/boards/cc2650stk/doc.txt b/boards/cc2650stk/doc.txt
@@ -127,7 +127,9 @@ advertising channels, as well as the corresponding variables in the RIOT
 command.
 
 ```
-typedef struct __attribute__ ((aligned(4))) {
+#include <stdalign.h>
+
+typedef struct alignas(4) {
     radio_op_command_t ropCmd;
     uint8_t channel;
     struct {

@@ -26,6 +26,8 @@
 #define XFA_H
 
 #include <inttypes.h>
+#include <stdalign.h>
+
 #include "compiler_hints.h"
 
 /*
@@ -45,7 +47,7 @@ _Pragma("GCC diagnostic ignored \"-Warray-bounds\"")
  */
 #define _XFA(type, name, prio) \
     NO_SANITIZE_ARRAY \
-    __attribute__((used, section(".xfa." #name "." #prio))) _Alignas(type) type
+    __attribute__((used, section(".xfa." #name "." #prio))) alignas(type) type
 
 /**
  * @brief helper macro for other XFA_* macros
@@ -54,7 +56,7 @@ _Pragma("GCC diagnostic ignored \"-Warray-bounds\"")
  */
 #define _XFA_CONST(type, name, prio) \
     NO_SANITIZE_ARRAY \
-    __attribute__((used, section(".roxfa." #name "." #prio))) _Alignas(type) type
+    __attribute__((used, section(".roxfa." #name "." #prio))) alignas(type) type
 
 /**
  * @brief Define a read-only cross-file array

@@ -16,8 +16,10 @@
  * @}
  */
 
+#include <stdalign.h>
 #include <stdint.h>
 #include <stdio.h>
+
 #include "arm_cpu.h"
 #include "irq.h"
 #include "sched.h"
@@ -26,12 +28,12 @@
 #define STACK_MARKER    (0x77777777)
 #define REGISTER_CNT    (12)
 
-__attribute__((used, section(".usr_stack"), aligned(4))) uint8_t usr_stack[USR_STACKSIZE];
-__attribute__((used, section(".und_stack"), aligned(4))) uint8_t und_stack[UND_STACKSIZE];
-__attribute__((used, section(".fiq_stack"), aligned(4))) uint8_t fiq_stack[FIQ_STACKSIZE];
-__attribute__((used, section(".irq_stack"), aligned(4))) uint8_t irq_stack[ISR_STACKSIZE];
-__attribute__((used, section(".abt_stack"), aligned(4))) uint8_t abt_stack[ABT_STACKSIZE];
-__attribute__((used, section(".svc_stack"), aligned(4))) uint8_t svc_stack[ISR_STACKSIZE];
+__attribute__((used, section(".usr_stack"))) alignas(4) uint8_t usr_stack[USR_STACKSIZE];
+__attribute__((used, section(".und_stack"))) alignas(4) uint8_t und_stack[UND_STACKSIZE];
+__attribute__((used, section(".fiq_stack"))) alignas(4) uint8_t fiq_stack[FIQ_STACKSIZE];
+__attribute__((used, section(".irq_stack"))) alignas(4) uint8_t irq_stack[ISR_STACKSIZE];
+__attribute__((used, section(".abt_stack"))) alignas(4) uint8_t abt_stack[ABT_STACKSIZE];
+__attribute__((used, section(".svc_stack"))) alignas(4) uint8_t svc_stack[ISR_STACKSIZE];
 
 #if (ISR_STACKSIZE % 4)
 #error "ISR_STACKSIZE must be a multiple of 4"
@@ -57,7 +59,7 @@
    /* make sure the stack is double word aligned (8 bytes) */
    /* This is required in order to conform with Procedure Call Standard for the
     * ARM® Architecture (AAPCS) */
    /* https://web.archive.org/web/20150316114702/http://infocenter.arm.com/help/topic/com.arm.doc.ihi0042e/IHI0042E_aapcs.pdf
     */
    if (((uint32_t) stk & 0x7) != 0) {
        /* add a single word padding */
@@ -144,7 +146,7 @@
    uint32_t *ptr = (uint32_t *)(uintptr_t)&irq_stack[0];
    uint32_t *end = (uint32_t *)(uintptr_t)&irq_stack[ISR_STACKSIZE];

    while(((*ptr) == STACK_CANARY_WORD) && (ptr < end)) {
        ++ptr;
    }


@@ -19,6 +19,7 @@
 #ifndef PERIPH_CPU_H
 #define PERIPH_CPU_H
 
+#include <stdalign.h>
 #include <stdbool.h>
 #include <stdint.h>
 #include "sdkconfig.h"
@@ -726,7 +727,7 @@ typedef struct {
 /**
  * @brief  SDIO/SDMMC buffer instantiation requirement for SDHC
  */
-#define SDMMC_CPU_DMA_REQUIREMENTS  __attribute__((aligned(SDMMC_CPU_DMA_ALIGNMENT)))
+#define SDMMC_CPU_DMA_REQUIREMENTS  alignas(SDMMC_CPU_DMA_ALIGNMENT)
 
 /**
  * @brief  SDIO/SDMMC buffer alignment for SDHC because of DMA/FIFO buffer restrictions

diff --git a/cpu/native/periph/flashpage.c b/cpu/native/periph/flashpage.c
@@ -19,6 +19,7 @@
  */
 
 #include <assert.h>
+#include <stdalign.h>
 #include <string.h>
 
 #include "cpu.h"
@@ -27,7 +28,7 @@
 #define ENABLE_DEBUG 0
 #include "debug.h"
 
-__attribute__((aligned(FLASHPAGE_SIZE * FLASHPAGE_NUMOF)))
+alignas(FLASHPAGE_SIZE * FLASHPAGE_NUMOF)
 char _native_flash[FLASHPAGE_SIZE * FLASHPAGE_NUMOF];
 
 void flashpage_erase(unsigned page)

@@ -417,7 +417,7 @@ typedef struct {
 /**
  * @brief USBDEV buffer instantiation requirement
  */
-#define USBDEV_CPU_DMA_REQUIREMENTS    __attribute__((aligned(USBDEV_CPU_DMA_ALIGNMENT)))
+#define USBDEV_CPU_DMA_REQUIREMENTS    alignas(USBDEV_CPU_DMA_ALIGNMENT)
 
 #if !defined(CPU_FAM_NRF51) && !defined(DOXYGEN)
 /**

diff --git a/cpu/riscv_common/irq_arch.c b/cpu/riscv_common/irq_arch.c
@@ -18,8 +18,9 @@
  * @}
  */
 
-#include <stdio.h>
 #include <inttypes.h>
+#include <stdalign.h>
+#include <stdio.h>
 
 #include "macros/xtstr.h"
 #include "cpu.h"
@@ -160,7 +161,7 @@ static void handle_trap(uword_t mcause)
 /* Marking this as interrupt to ensure an mret at the end, provided by the
  * compiler. Aligned to 64-byte boundary as per RISC-V spec and required by some
  * of the supported platforms (gd32)*/
-__attribute((aligned(64)))
+alignas(64)
 static void __attribute__((interrupt)) trap_entry(void)
 {
     __asm__ volatile (

@@ -21,6 +21,8 @@
 #ifndef PERIPH_CPU_COMMON_H
 #define PERIPH_CPU_COMMON_H
 
+#include <stdalign.h>
+
 #include "cpu.h"
 #include "exti_config.h"
 #include "timer_config.h"
@@ -992,7 +994,7 @@ typedef struct {
 /**
  * @brief USBDEV buffer instantiation requirement
  */
-#define USBDEV_CPU_DMA_REQUIREMENTS    __attribute__((aligned(USBDEV_CPU_DMA_ALIGNMENT)))
+#define USBDEV_CPU_DMA_REQUIREMENTS    alignas(USBDEV_CPU_DMA_ALIGNMENT)
 
 /**
  * @brief USB peripheral parameters
@@ -1015,7 +1017,7 @@ typedef struct {
 /**
  * @brief SDIO/SDMMC buffer instantiation requirement for SDHC
  */
-#define SDMMC_CPU_DMA_REQUIREMENTS  __attribute__((aligned(SDMMC_CPU_DMA_ALIGNMENT)))
+#define SDMMC_CPU_DMA_REQUIREMENTS  alignas(SDMMC_CPU_DMA_ALIGNMENT)
 
 /**
  * @brief SDHC peripheral configuration

@@ -78,8 +78,8 @@ struct eth_buf_desc {
 /* GMAC buffer descriptors */
 #define GMAC_DESC_ALIGNMENT 8
 #define GMAC_BUF_ALIGNMENT  32
-static struct eth_buf_desc rx_desc[ETH_RX_BUFFER_COUNT] __attribute__((aligned(GMAC_DESC_ALIGNMENT)));
-static struct eth_buf_desc tx_desc[ETH_TX_BUFFER_COUNT] __attribute__((aligned(GMAC_DESC_ALIGNMENT)));
+static alignas(GMAC_DESC_ALIGNMENT) struct eth_buf_desc rx_desc[ETH_RX_BUFFER_COUNT];
+static alignas(GMAC_DESC_ALIGNMENT) struct eth_buf_desc tx_desc[ETH_TX_BUFFER_COUNT];
 
 static struct eth_buf_desc *rx_curr;
 static struct eth_buf_desc *tx_curr;
@@ -89,8 +89,8 @@ static struct eth_buf_desc *tx_curr;
 static uint8_t  tx_idx;
 static uint8_t  rx_idx;
 
-static uint8_t  rx_buf[ETH_RX_BUFFER_COUNT][ETH_RX_BUFFER_SIZE] __attribute__((aligned(GMAC_BUF_ALIGNMENT)));
-static uint8_t  tx_buf[ETH_TX_BUFFER_COUNT][ETH_TX_BUFFER_SIZE] __attribute__((aligned(GMAC_BUF_ALIGNMENT)));
+static alignas(GMAC_BUF_ALIGNMENT) uint8_t  rx_buf[ETH_RX_BUFFER_COUNT][ETH_RX_BUFFER_SIZE];
+static alignas(GMAC_BUF_ALIGNMENT) uint8_t  tx_buf[ETH_TX_BUFFER_COUNT][ETH_TX_BUFFER_SIZE];
 extern sam0_eth_netdev_t _sam0_eth_dev;
 
 static bool _is_sleeping;

@@ -19,6 +19,7 @@
 #ifndef PERIPH_CPU_SDMMC_H
 #define PERIPH_CPU_SDMMC_H
 
+#include <stdalign.h>
 #include <stdint.h>
 
 #include "periph/cpu_dma.h"
@@ -45,7 +46,7 @@ extern "C" {
 /**
  * @brief SDIO/SDMMC buffer instantiation requirement for STM32
  */
-#define SDMMC_CPU_DMA_REQUIREMENTS  __attribute__((aligned(SDMMC_CPU_DMA_ALIGNMENT)))
+#define SDMMC_CPU_DMA_REQUIREMENTS  alignas(SDMMC_CPU_DMA_ALIGNMENT)
 
 /**
  * @brief SDIO/SDMMC pin structure for STM32

@@ -21,6 +21,7 @@
 #ifndef PERIPH_CPU_USBDEV_H
 #define PERIPH_CPU_USBDEV_H
 
+#include <stdalign.h>
 #include <stdint.h>
 
 #include "periph/cpu_gpio.h"
@@ -37,7 +38,7 @@ extern "C" {
 /**
  * @brief USBDEV buffer instantiation requirement
  */
-#define USBDEV_CPU_DMA_REQUIREMENTS    __attribute__((aligned(USBDEV_CPU_DMA_ALIGNMENT)))
+#define USBDEV_CPU_DMA_REQUIREMENTS    alignas(USBDEV_CPU_DMA_ALIGNMENT)
 
 /**
  * @brief stm32 USB device FS configuration

@@ -48,6 +48,7 @@
 #ifndef PERIPH_FLASHPAGE_H
 #define PERIPH_FLASHPAGE_H
 
+#include <stdalign.h>
 #include <stddef.h>
 #include <stdint.h>
 
@@ -171,7 +172,7 @@ enum {
  * @param[in] size size of the array in unit of @ref FLASHPAGE_SIZE
  */
 #define FLASH_WRITABLE_INIT(name, size) \
-    __attribute__((aligned(FLASHPAGE_SIZE))) \
+    alignas(FLASHPAGE_SIZE) \
     __attribute__((section(".flash_writable." #name))) \
     static const uint8_t name [size * FLASHPAGE_SIZE]
 #endif

diff --git a/drivers/mtd_flashpage/mtd_flashpage.c b/drivers/mtd_flashpage/mtd_flashpage.c
@@ -21,9 +21,10 @@
  * @}
  */
 
-#include <string.h>
-#include <errno.h>
 #include <assert.h>
+#include <errno.h>
+#include <stdalign.h>
+#include <string.h>
 
 #include "architecture.h"
 #include "cpu.h"
@@ -114,8 +115,7 @@ static int _write_page(mtd_dev_t *dev, const void *buf, uint32_t page, uint32_t
 
     if ((addr % FLASHPAGE_WRITE_BLOCK_ALIGNMENT) || (size < FLASHPAGE_WRITE_BLOCK_SIZE) ||
         ((uintptr_t)buf % FLASHPAGE_WRITE_BLOCK_ALIGNMENT)) {
-        uint8_t tmp[FLASHPAGE_WRITE_BLOCK_SIZE]
-                __attribute__ ((aligned (FLASHPAGE_WRITE_BLOCK_ALIGNMENT)));
+        uint8_t alignas(FLASHPAGE_WRITE_BLOCK_ALIGNMENT) tmp[FLASHPAGE_WRITE_BLOCK_SIZE];
 
         offset = addr % FLASHPAGE_WRITE_BLOCK_ALIGNMENT;
         size = MIN(size, FLASHPAGE_WRITE_BLOCK_SIZE - offset);

diff --git a/examples/lua_REPL/main.c b/examples/lua_REPL/main.c
@@ -18,6 +18,7 @@
  * @}
  */
 
+#include <stdalign.h>
 #include <stdio.h>
 #include <string.h>
 
@@ -31,7 +32,7 @@
  */
 #define MAIN_LUA_MEM_SIZE (40000)
 
-static char lua_memory[MAIN_LUA_MEM_SIZE] __attribute__ ((aligned(__BIGGEST_ALIGNMENT__)));
+static alignas(__BIGGEST_ALIGNMENT__) char lua_memory[MAIN_LUA_MEM_SIZE];
 
 #define BARE_MINIMUM_MODS (LUAR_LOAD_BASE | LUAR_LOAD_IO | LUAR_LOAD_CORO | LUAR_LOAD_PACKAGE)
 

diff --git a/examples/lua_basic/main.c b/examples/lua_basic/main.c
@@ -18,6 +18,7 @@
  * @}
  */
 
+#include <stdalign.h>
 #include <stdio.h>
 #include <errno.h>
 
@@ -32,7 +33,7 @@
 #else
 #define LUA_MEM_SIZE (11000)
 #endif
-static char lua_mem[LUA_MEM_SIZE] __attribute__ ((aligned(__BIGGEST_ALIGNMENT__)));
+static alignas(__BIGGEST_ALIGNMENT__) char lua_mem[LUA_MEM_SIZE];
 
 int lua_run_script(const uint8_t *buffer, size_t buffer_len)
 {

diff --git a/sys/include/architecture.h b/sys/include/architecture.h
@@ -24,9 +24,10 @@
 #ifndef ARCHITECTURE_H
 #define ARCHITECTURE_H
 
-#include <stdint.h>
 #include <inttypes.h>
 #include <limits.h>
+#include <stdalign.h>
+#include <stdint.h>
 
 #include "architecture_arch.h" /* IWYU pragma: export */
 
@@ -203,7 +204,7 @@ typedef uintptr_t   uinttxtptr_t;
  * char WORD_ALIGNED thread_stack[THREAD_STACKSIZE_DEFAULT];
  * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  */
-#define WORD_ALIGNED __attribute__((aligned(ARCHITECTURE_WORD_BYTES)))
+#define WORD_ALIGNED alignas(ARCHITECTURE_WORD_BYTES)
 
 /**
  * @brief       Check if @p addr is alignment to @p alignment

diff --git a/sys/include/can/can.h b/sys/include/can/can.h
@@ -26,12 +26,13 @@
 #ifndef CAN_CAN_H
 #define CAN_CAN_H
 
+#include <stdalign.h>
+#include <stdint.h>
+
 #ifdef __cplusplus
 extern "C" {
 #endif
 
-#include <stdint.h>
-
 #if defined(__linux__)
 
 #include <linux/can.h>
@@ -92,7 +93,7 @@ struct can_frame {
     uint8_t __res0;  /**< reserved / padding */
     uint8_t __res1;  /**< reserved / padding */
     /** Frame data */
-    uint8_t data[CAN_MAX_DLEN] __attribute__((aligned(8)));
+    uint8_t alignas(8) data[CAN_MAX_DLEN];
 };
 
 /**

diff --git a/sys/include/event.h b/sys/include/event.h
@@ -153,7 +153,8 @@ struct event {
 /**
  * @brief   event queue structure
  */
-typedef struct PTRTAG {
+typedef struct {
+    PTRTAG
     clist_node_t event_list;    /**< list of queued events              */
     thread_t *waiter;           /**< thread owning event queue          */
 } event_queue_t;

diff --git a/sys/include/pm_layered.h b/sys/include/pm_layered.h
@@ -55,8 +55,9 @@ extern "C" {
  * @brief Power Management mode blocker typedef
  */
 typedef struct {
+    WORD_ALIGNED
     uint8_t blockers[PM_NUM_MODES];     /**< number of blockers for the mode */
-} WORD_ALIGNED pm_blocker_t;
+} pm_blocker_t;
 
 /**
  * @brief   Block a power mode

diff --git a/sys/include/ptrtag.h b/sys/include/ptrtag.h
@@ -63,6 +63,7 @@
 
 #include <assert.h>
 #include <inttypes.h>
+#include <stdalign.h>
 #include <stdint.h>
 
 #ifdef __cplusplus
@@ -74,7 +75,7 @@ extern "C" {
  *
  * @details This will ensure a minimum alignment of 4 bytes
  */
-#define PTRTAG  __attribute__((aligned(4)))
+#define PTRTAG  alignas(4)
 
 /**
  * @brief   Create a tagged pointer

diff --git a/sys/include/riotboot/flashwrite.h b/sys/include/riotboot/flashwrite.h
@@ -59,6 +59,8 @@
 #ifndef RIOTBOOT_FLASHWRITE_H
 #define RIOTBOOT_FLASHWRITE_H
 
+#include <stdalign.h>
+
 #ifdef __cplusplus
 extern "C" {
 #endif
@@ -94,7 +96,7 @@ extern "C" {
  * @brief Extra attributes required for the firmware intermediate buffer
  */
 #define RIOTBOOT_FLASHPAGE_BUFFER_ATTRS \
-    __attribute__((aligned(FLASHPAGE_WRITE_BLOCK_ALIGNMENT)))
+    alignas(FLASHPAGE_WRITE_BLOCK_ALIGNMENT)
 
 /**
  * @brief   firmware update state structure