STM32CubeMX H7 USB CDC bug: usbd_desc.c Get_SerialNum() uninitialized variables cause HardFault on -O1/-O2

[ICT_TAN]

There is a critical code-generation template bug in STM32CubeMX (reproduced in 6.16.1 with STM32CubeH7) when generating USB Device middleware configurations. In the generated usbd_desc.c file, the Get_SerialNum() function is generated with uninitialized local variables that are then used in arithmetic operations.

This results in Undefined Behavior (UB). It compiles and works under -O0 because the uninitialized stack happens to evaluate to zero, but it causes an immediate, silent HardFault/BusFault during USB enumeration on Windows when compiled with -O1 or -O2 optimizations

original generated code 

static void Get_SerialNum(void)
{
  uint32_t deviceserial0; // Uninitialized
  uint32_t deviceserial1; // Uninitialized
  uint32_t deviceserial2; // Uninitialized

  // ST's generator template completely misses the lines assigning the registers!
  deviceserial0 += deviceserial2; // Undefined Behavior: addition on uninitialized variables

  if (deviceserial0 != 0)
  {
    IntToUnicode(deviceserial0, &USBD_StringSerial[2], 8);
    IntToUnicode(deviceserial1, &USBD_StringSerial[18], 4);
  }
}

//proposed fix or at least working code
static void Get_SerialNum(void)
{
  uint32_t deviceserial0;
  uint32_t deviceserial1;
  uint32_t deviceserial2;

  /* Explicitly read the Unique Device ID (UID) from the hardware */
  deviceserial0 = HAL_GetUIDw0();
  deviceserial1 = HAL_GetUIDw1();
  deviceserial2 = HAL_GetUIDw2();

  deviceserial0 += deviceserial2;

  if (deviceserial0 != 0)
  {
    IntToUnicode(deviceserial0, &USBD_StringSerial[2], 8);
    IntToUnicode(deviceserial1, &USBD_StringSerial[18], 4);
  }
}

 

[Ghofrane GSOURI]

Hello ​@ICT_TAN 

 

Could you please retest this using the latest version of STM32CubeMX 6.18.0 and confirm whether the issue still occurs?

Download STM32CubeMX6.18.0  from  here 

THX

Ghofrane

 

 

[ICT_TAN]

Hi ​@Ghofrane GSOURI thanks for the quick reply.
Even with 1.18.0 and STM32Cube FW_H7 V1.13.0 instead of  FW_H7 V1.12.1 the error sadly still persist leaving those variables uninitialised.
Furthermore when migrating from 1.16.1 to 1.18 i now get warned, that the peripheral base clock of 240MHz should now be below or equal to 225Mhz despite showing a tooltip of 240Hz max.

[Ghofrane GSOURI]

Hello ​@ICT_TAN 

Could you please provide your IOC.

THX

Ghofrane

[ICT_TAN]

Hi ​@Ghofrane GSOURI 
sadly i did not get clearance to share the whole file, are there certain sections of relevance/importants here like only USB_DEVICE section eg.

Greetings
Jonathan

[ICT_TAN]

​@Ghofrane GSOURI 
Though not the original project here is a .ioc of a demo project with just fs and hs enabled.
The generated code still holds the uninitialized variables.
I dug a bit further and usbd_desc_template.c holds the “correct” assignment 

deviceserial0 = *(uint32_t *)DEVICE_ID1;

deviceserial1 = *(uint32_t *)DEVICE_ID2;

deviceserial2 = *(uint32_t *)DEVICE_ID3;

 
Maybe I configured smth wrong def not a straight forward process ^^;

 

[Ghofrane GSOURI]

Hello ​@ICT_TAN 

Your contribution is much appreciated.

Issue has been escalated to dev team under internal ticker ID #0063998

I will keep you posted with updates.

THX

Ghofrane