G.5.2 ARC Features

ARC processors are so configurable that even core registers and their numbers are not predetermined completely. Moreover, flags and PC registers, which are important to GDB, are not “core” registers in ARC. Therefore, there are two features that their presence is mandatory: ‘org.gnu.gdb.arc.core’ and ‘org.gnu.gdb.arc.aux’.

The ‘org.gnu.gdb.arc.core’ feature is required for all targets. It must contain registers:

• - ‘r0’ through ‘r25’ for normal register file targets.
• - ‘r0’ through ‘r3’, and ‘r10’ through ‘r15’ for reduced register file targets.
• - ‘gp’, ‘fp’, ‘sp’, ‘r30’²¹, ‘blink’, ‘lp_count’, ‘pcl’.

In case of an ARCompact target (ARCv1 ISA), the ‘org.gnu.gdb.arc.core’ feature may contain registers ‘ilink1’ and ‘ilink2’. While in case of ARC EM and ARC HS targets (ARCv2 ISA), register ‘ilink’ may be present. The difference between ARCv1 and ARCv2 is the naming of registers 29th and 30th. They are called ‘ilink1’ and ‘ilink2’ for ARCv1 and are optional. For ARCv2, they are called ‘ilink’ and ‘r30’ and only ‘ilink’ is optional. The optionality of ‘ilink*’ registers is because of their inaccessibility during user space debugging sessions.

Extension core registers ‘r32’ through ‘r59’ are optional and their existence depends on the configuration. When debugging GNU/Linux applications, i.e. user space debugging, these core registers are not available.

The ‘org.gnu.gdb.arc.aux’ feature is required for all ARC targets. Here is the list of registers pertinent to this feature:

• - mandatory: ‘pc’ and ‘status32’.
• - optional: ‘lp_start’, ‘lp_end’, and ‘bta’.