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    • STM32H7 strcat bug

    Posted by maryjane on 2018-02-11 15:29

    Hello.
    I was wondering about a Hard Fault.
    Stepping through I notice strcat() uses the string content as the address for the destination.
    In the function there is an extra command
    ldr r0, [[r3, #0]] (why?)
    to load the content from the address, instead of using a simple
    mov r0, r3

    Image

    Thank you.

    Reads: 9871
    Posted by dautrevaux on 2018-02-11 20:02 France

    Hi,

    There's no bug in strcat; the line you don't understand loads the first 4 bytes from PCC_VERSION ("2.08") then stores them at the end of msgStr (r2 contains the length of msgStr, that is the number of bytes before the first zero-byte in msgStr).

    Strcat is effectively a dangerous function for two reasons:

    1. You may overflow the destination buffer, as strcat can't make any check
    2. If ever the destination string was not initialized, the initial strlen may yield a very big value and you will write somewhere where you don't expect...


    So I urge you to check your code, but I can ensure you the strcat code is correct...

    Hope this helps,

    Bernard (Ac6)

         Posted by maryjane on 2018-02-11 22:39

    You are right. I read STR in the wrong way.
    And I found the reason of the hard fault:
    In MPU_Config there was a mistyped size of MPU_REGION_SIZE_512MB
    instead of MPU_REGION_SIZE_512KB. The area where strcat() has to
    copy the data to was protected.
    I'm sorry for the inconvenience.


     
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