The MSP430 target supports an attribute "persistent" that can be set on variables to indicate that they should be placed in a special section ".persistent", which will not be re-initialized on reset.
As reported in PR78818 (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78818), GCC does not place variables with the persistent attribute in the .persistent section if: 1) If -fdata-sections is used. 2) If -mdata-region={lower,upper,either} is used. 3) They are static and initialized to 0 (or uninitialized). The first of the two following patch fixes these issues by always setting the section of a variable with the .persistent attribute to .persistent. The second patch adds a warning if the persistent attribute is used on an automatic variable, to warn that this will have no effect. The patches passed regression testing with "-mcpu=msp430x/-mlarge" for msp430-elf on the gcc-6-branch (r247086). Trunk doesn't build with C++ support for msp430-elf which is why gcc-6-branch was used.
