[Agent] Bug Fix - Fixed Processor Arch Detection in Windows - AB#2232751

[AdityaMankal-MS]

Context

Installation script of Pipeline Agent reads the PROCESSOR_ARCHITECTURE environment variable to determine the processor's make (AMD, Intel, ARM) and OS architecture (32 bit or 64 bit).
function detect_platform_and_runtime_id()

Issue

PROCESSOR_ARCHITECTURE environment variable will be returned as what's most capable when running the external process i.e., the returned value varies depending on which process this environment variable is read from. The installation script of Agent uses Bash to run the dev.sh script when being setup on any Windows machine. Doing this leads to the value always being read as AMD64 - even on 32bit Windows or ARM hardware.

Why did our CI pipeline not catch this?

detect_platform_and_runtime_id function is not involved when running via the CI pipeline as the target architecture is passed as an argument to the setup scripts i.e., the PROCESSOR_ARCHITECTURE variable is not read to determine the underlying architecture.

Who is affected?

Anyone building the Agents on a 32bit Windows or ARM Windows is affected as the build always defaults to x64.

How can this be fixed?

• Rely on the PROCESSOR_IDENTIFIER variable instead of the PROCESSOR_ARCHITECTURE to understand the Processor make (Intel, AMD or ARM)
• Rely on the uname command to understand if the OS is 32bit or 64bit.

Here are the tested combinations of these variables:

CPU Arch	OS	PROCESSOR_IDENTIFIER	uname -m
Intel 64	Windows 64	Intel64 Family 6 Model 140 Stepping 1, GenuineIntel	x86_64
AMD 64	Windows 64	AMD64 Family 25 Model 1 Stepping 1, AuthenticAMD	x86_64
ARM 64	Windows ARM	ARMv8 (64-bit) Family 8 Model D0C Revision 301, Ampere(R)	x86_64

How was the fix tested?

• PROCESSOR_IDENTIFIER environment variable value does not change depending on the process it is read from.
  

Layout output on Windows x64

Layout output on Windows ARM64