https://developer.arm.com/documentation/dui0491/i/Compiler-specific-Features/--align

This keyword from ARM Compiler V5. For example this is part from HAL library

#if defined (__ARMCC_VERSION) && (__ARMCC_VERSION >= 6010050) /* ARM Compiler V6 */
  #ifndef __ALIGN_BEGIN
    #define __ALIGN_BEGIN
  #endif
  #ifndef __ALIGN_END
    #define __ALIGN_END      __attribute__ ((aligned (4)))
  #endif
#elif defined ( __GNUC__ ) && !defined (__CC_ARM) /* GNU Compiler */
  #ifndef __ALIGN_END
    #define __ALIGN_END    __attribute__ ((aligned (4)))
  #endif /* __ALIGN_END */
  #ifndef __ALIGN_BEGIN  
    #define __ALIGN_BEGIN
  #endif /* __ALIGN_BEGIN */
#else
  #ifndef __ALIGN_END
    #define __ALIGN_END
  #endif /* __ALIGN_END */
  #ifndef __ALIGN_BEGIN      
    #if defined   (__CC_ARM)      /* ARM Compiler V5*/
      #define __ALIGN_BEGIN    __align(4)
    #elif defined (__ICCARM__)    /* IAR Compiler */
      #define __ALIGN_BEGIN 
    #endif /* __CC_ARM */
  #endif /* __ALIGN_BEGIN */
#endif /* __GNUC__ */

/* Macro to get variable aligned on 32-bytes,needed for cache maintenance 
purpose */
#if defined   (__GNUC__)      /* GNU Compiler */
  #define ALIGN_32BYTES(buf)  buf __attribute__ ((aligned (32)))
#elif defined (__ICCARM__)    /* IAR Compiler */
  #define ALIGN_32BYTES(buf) _Pragma("data_alignment=32") buf
#elif defined (__CC_ARM)      /* ARM Compiler */
  #define ALIGN_32BYTES(buf) __align(32) buf
#endif
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