__attribute__((zero_init)) variable attribute

The section attribute specifies that a variable must be placed in a particular data section. The zero_init attribute specifies that a variable with no initializer is placed in a ZI data section. If an initializer is specified, an error is reported.

__attribute__((zero_init)) int x;                    /* in section ".bss" */
__attribute__((section("mybss"), zero_init)) int y;  /* in section "mybss" */