trezor-firmware/core/embed/prepare/startup_stm32u5.s

  .syntax unified

  .text

  .global reset_handler
  .type reset_handler, STT_FUNC
reset_handler:
  // set the stack protection
  ldr r0, =_sstack
  add r0, r0, #16        // padding
  msr MSPLIM, r0

  bl SystemInit

  // read the first rng data and save it
  ldr r0, =0            // r0 - previous value
  ldr r1, =0            // r1 - whether to compare the previous value
  bl rng_read

  // read the next rng data and make sure it is different than previous
  // r0 - value returned from previous call
  ldr r1, =1            // r1 - whether to compare the previous value
  bl rng_read
  mov r4, r0            // save TRNG output in r4

  // wipe memory to remove any possible vestiges of sensitive data


fill_ram:
  ldr r0, =sram1_start   // r0 - point to beginning of SRAM
  ldr r1, =sram1_end     // r1 - point to byte after the end of SRAM
  mov r2, r4             // r2 - the word-sized value to be written
  bl memset_reg

  ldr r0, =sram2_start   // r0 - point to beginning of SRAM
  ldr r1, =sram2_end     // r1 - point to byte after the end of SRAM
  mov r2, r4             // r2 - the word-sized value to be written
  bl memset_reg

  ldr r0, =sram3_start   // r0 - point to beginning of SRAM
  ldr r1, =sram3_end     // r1 - point to byte after the end of SRAM
  mov r2, r4             // r2 - the word-sized value to be written
  bl memset_reg

  ldr r0, =sram4_start   // r0 - point to beginning of SRAM
  ldr r1, =sram4_end     // r1 - point to byte after the end of SRAM
  mov r2, r4             // r2 - the word-sized value to be written
  bl memset_reg

  ldr r0, =sram5_start   // r0 - point to beginning of SRAM
  ldr r1, =sram5_end     // r1 - point to byte after the end of SRAM
  mov r2, r4             // r2 - the word-sized value to be written
  bl memset_reg

  ldr r0, =sram6_start   // r0 - point to beginning of SRAM
  ldr r1, =sram6_end     // r1 - point to byte after the end of SRAM
  mov r2, r4             // r2 - the word-sized value to be written
  bl memset_reg


  // setup environment for subsequent stage of code


clear_ram:
  ldr r2, =0             // r2 - the word-sized value to be written
  ldr r0, =sram1_start   // r0 - point to beginning of SRAM
  ldr r1, =sram1_end     // r1 - point to byte after the end of SRAM
  bl memset_reg
  ldr r0, =sram2_start   // r0 - point to beginning of SRAM
  ldr r1, =sram2_end     // r1 - point to byte after the end of SRAM
  bl memset_reg
  ldr r0, =sram3_start   // r0 - point to beginning of SRAM
  ldr r1, =sram3_end     // r1 - point to byte after the end of SRAM
  bl memset_reg
  ldr r0, =sram4_start   // r0 - point to beginning of SRAM
  ldr r1, =sram4_end     // r1 - point to byte after the end of SRAM
  bl memset_reg
  ldr r0, =sram5_start   // r0 - point to beginning of SRAM
  ldr r1, =sram5_end     // r1 - point to byte after the end of SRAM
  bl memset_reg
  ldr r0, =sram6_start   // r0 - point to beginning of SRAM
  ldr r1, =sram6_end     // r1 - point to byte after the end of SRAM
  bl memset_reg

  // copy data in from flash
  ldr r0, =data_vma     // dst addr
  ldr r1, =data_lma     // src addr
  ldr r2, =data_size    // size in bytes
  bl memcpy

  // copy sensitive data in from flash
  ldr r0, =sensitive_vma     // dst addr
  ldr r1, =sensitive_lma     // src addr
  ldr r2, =sensitive_size    // size in bytes
  bl memcpy

  // setup the stack protector (see build script "-fstack-protector-all") with an unpredictable value
  bl rng_get
  ldr r1, = __stack_chk_guard
  str r0, [r1]

  // enter the application code
  bl main

  b shutdown_privileged

  .end