Possible problems when changing compiler version to >= 10

[kemonats]

If you plan to change your gcc compiler version to >= 10 then you may experience the following problems:

1. the compiler, in the case of a simple loop writing a constant value to cells of memory may use memset() function, which is not defined. For example, such loops:

   https://github.com/phoenix-rtos/phoenix-rtos-kernel/blob/1c700bbab4851a4d9010ddc4ff1b14fcada19295/lib/printf.c#L114-L115

               while (pad_len-- > 0)
                       *out++ = ' ';

   https://github.com/phoenix-rtos/phoenix-rtos-kernel/blob/1c700bbab4851a4d9010ddc4ff1b14fcada19295/hal/armv7a/pmap.c#L546-L549

       for (i = 0; i < sizeof(pmap_common.asid_map) / sizeof(pmap_common.asid_map[0]); ++i) {
               pmap_common.asid_map[i] = NULL;
               pmap_common.asids[i] = i;
       }

   Solution:

   • adding the -ffreestanding option to the CFLAGS in Makefile.common or in the Makefile in the kernel and plo repository.

2. since version 10 gcc, the default option is -fno-common ( 9 has -fcommon set as default) This causes a problem with linking the libjffs2 library. This is caused by the definition of the init_user_ns variable as global in the header file: https://github.com/phoenix-rtos/phoenix-rtos-filesystems/blob/8af595a6b37129b4a6cb7e0cb93705c4d6b3476b/jffs2/phoenix-rtos.h#L139

   struct user_namespace init_user_ns;

   Solution:

   • define the init_user_ns variable in one of the source files, and in the header file declare this variable.as extern.
   • compile the source files that make up this library with the -fcommon option.

[nalajcie]

Thanks for bringing it to our attention.

Regarding the (1):

• IMHO plo / kernel should be compiled with -ffreestanding as they are being run in C freestanding environment
• adding the -ffreestanding option is not enough for gcc to avoid memset problems (see my comment here: https://github.com/phoenix-rtos/plo/pull/167#issuecomment-1072521885) - it explicitly requires mem* functions to be implemented even in freestanding environment

[badochov]

2) Fixed as of https://github.com/phoenix-rtos/phoenix-rtos-filesystems/pull/125 and https://github.com/phoenix-rtos/phoenix-rtos-build/pull/181