This is part of a linux device driver.

uint32_t val = 0;
static long axpu_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
{
...
 copy_from_user(&val,(int32_t *)arg, sizeof(val));
...
}

I can compile this ok and was doing some debug. To keep from some codes from being optimized away. I changed the code like this.

#pragma GCC push_options
#pragma GCC optimize ("O0")
uint32_t val = 0;
static long axpu_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
{
...
 copy_from_user(&val,(int32_t *)arg, sizeof(val));   // <-- line 364
...
}
#pragma GCC pop_options

This is a trick I've been using for a while and worked just fine.(just that I used in the linux kernel codes for boot debug). This time, I'm doing it for the device driver. Now the compiler gives me this error.

In file included from ./arch/arm64/include/asm/preempt.h:5,
                 from ./include/linux/preempt.h:78,
                 from ./include/linux/spinlock.h:51,
                 from ./include/linux/seqlock.h:36,
                 from ./include/linux/time.h:6,
                 from ./arch/arm64/include/asm/stat.h:12,
                 from ./include/linux/stat.h:6,
                 from ./include/linux/module.h:10,
                 from /home/ckim/testlin540/axpu_ldd_kc.c:8:
In function 'check_copy_size',
    inlined from 'copy_from_user' at ./include/linux/uaccess.h:143:6,
    inlined from 'axpu_ioctl' at /home/ckim/testlin540/axpu_ldd_kc.c:364:4:
./include/linux/thread_info.h:160:4: error: call to '__bad_copy_to' declared with attribute error: copy destination size is too small
  160 |    __bad_copy_to();
      |    ^~~~~~~~~~~~~~~

I tried putting the #pragma thing around #include <linux/uaccess.h> in vain.
Some say it's gcc problem but I'm not sure. This is linux-5.4.188 code and this is the compiler version.

ckim@ckim-ubuntu:~/testlin540$ aarch64-none-linux-gnu-gcc --version
aarch64-none-linux-gnu-gcc (GNU Toolchain for the A-profile Architecture 10.2-2020.11 (arm-10.16)) 10.2.1 20201103
Copyright (C) 2020 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.