For example, I have a zero-initialized buffer with a capacity of 512 bytes, with 390 bytes filled with non-null data. I attempt to copy 32 additional bytes onto the buffer like this:
Code: copy.c Select all
// preserve original contents of *out* for debugging
char* preMemcpy = malloc(512);
memcpy(preMemcpy, out, 390);
// copy new data into *out*
memcpy(out + 390, newData, 32);
After that, I have a breakpoint that gets hit if there are any null characters in the out buffer. The breakpoint is hit sometimes, but not always.When the breakpoint is hit, I'm using the debugger to inspect everything.
The last time this happened, out had 388 bytes of data that matched preMemcpy (instead of 390 bytes), followed by two null characters, followed by all 32 bytes from newData. So somehow, two bytes were "deleted".
What's even more alarming is that this is happening in the bytes prior to the block provided to memcpy. Even though I'm specifying out + 390, it's bytes 388 and 389 that are being replaced by null characters.
This is happening in memory that should be byte-addressable, since it's allocated using:
Code: Select all
heap_caps_malloc(byte_count, MALLOC_CAP_SPIRAM|MALLOC_CAP_8BIT)
