Machine Information

Processor Features

There are multiple levels of feature that a CPU must implement according to the processor specification. These are called micro-architecture levels. For x86-64, these are: x86-64-v2, x86-64-v3 and x86-64-v4 .

Fig 1.1 - CPU Micro-architecture levels

• Levels x86-64-v3 and x86-64-v4 are only available if the features are fully enabled.
• The names are expected to be used as directory names by linkers and compilers.
• To build with a given level, the programmer can build a shared object using -march=x86-64-v3 (or other suitable) GCC flag.
• The resulting shared object is then installed in /usr/lib64/glibc-hwcaps/x86-64-v3 or /usr/lib/x86_64-linux-gnu/glibc-hwcaps/x86-64-v3 .

Data Types — Size and Alignments

Fig 1.1 - Sizes of static types

For types of N-bit integers

• If $N<=64$ : they have the same size and alignment as the smallest scalar type (char, short, etc.) that can contain them.
• If $N > 64$ : treated as struct of 64-bit integer chunks.The size is the $64*N$ where $N$ is the number of chunks that can contain the type, but the alignment is 64-bits.

For Bitfields:

• They are allocated from right to left.
• Must be contained in a type that can store them.
• Can be shared using unions and with other struct members.