Hi Linaro Toolchain Group,

I am going through the binutils code base specific to arm & aarch64. Please give some insight on below questions.

1. In the struct bfd_arch_info {...} (in bfd/bfd-in2.h) there are two fields 'enum bfd_architecture arch' and 'unsigned long mach'.

I went trough the binutils porting guide (by MR.Swami.Reddy@nsc.com) which says 'arch' is for architecture & 'mach' is for machine value.

At present in the bfd/bfd-in2.h :- arch = bfd_arch_aarch64 and mach = bfd_mach_aarch64 or bfd_mach_aarch64_ilp32.

But what these fields really means ? What is the difference between 'arch' and 'mach'?

Lets say instruction set architecture is ARMv8 (also known as aarch64 for 64 bit- if I am not wrong). Then we have specific implementation of this like cortex53, cortex57, Cavium ThunderX etc. With respect to this what will be the value of arch = ? and mach = ?

   

2. In the include/opcode/arm.h the 'arm_feature_set' is defined as a structure where as in include/opcode/aarch64.h 'aarch64_feature_set' is defined as unsigned long. Is there any specific reason for this? Why structure definition was not followed in aarch64 ?

typedef struct

{

unsigned long core;

unsigned long coproc;

} arm_feature_set;

    typedef unsigned long aarch64_feature_set;

3. Also I see that in the case of arm, 'mach' values are derived from cpu extension value specified in that 'arm_feature_set' structure.

   For example.

if (ARM_CPU_HAS_FEATURE (cpu_variant, arm_cext_iwmmxt2))

mach = bfd_mach_arm_iWMMXt2;

   Whereas in aarch64 mach is derived based on API type (64 or 32). Any reason for this ?

   mach = ilp32_p ? bfd_mach_aarch64_ilp32 : bfd_mach_aarch64;

   

Thanks in advance.