GoArm, MinimumRequirements: add documentation on GOARM64

Go 1.23 introduced GOARM64 environment variable; this patch documents
it.

Related to golang/go#69124

Change-Id: I148b1295d8772041f2379771a2f2e682fd4bfdbe
Reviewed-on: https://go-review.googlesource.com/c/wiki/+/609855
Reviewed-by: Cherry Mui <[email protected]>

Author: andreybokhanko

GoArm.md

@@ -17,6 +17,7 @@ Go supports the following ARM architectural families.
 | ARMv6            | supported  | GOARM=6         | GOARCH=arm       |
 | ARMv7            | supported  | GOARM=7         | GOARCH=arm       |
 | ARMv8            | supported  | n/a             | GOARCH=arm64     |
+| ARMv9            | supported  | n/a             | GOARCH=arm64     |
 
 Starting from Go 1.1, the appropriate GOARM value will be chosen if you compile the program from source on the target machine. In cross compilation situations, it is recommended that you always set an appropriate GOARM value along with GOARCH.
 

MinimumRequirements.md

@@ -115,7 +115,15 @@ See https://go.dev/doc/install/source#environment
 
 ### arm64
 
-All ARMv8-A processors.
+Until Go 1.23, the Go compiler always generated ARM64 binaries that could be executed by any ARMv8-A processor.
+
+Go 1.23 introduced a new `GOARM64` environment variable, which specifies the minimum target version of the ARM64 architecture at compile time. Allowed values are `v8.{0-9}` and `v9.{0-5}`. This may be followed by an option specifying extensions implemented by target hardware. Valid options are `,lse` and `,crypto`.
+
+Setting, for example, `GOARM64=v8.0,lse`, will allow the Go compiler to use LSE instructions in the generated binaries (which may improve performance in some cases); but these binaries will not run on older ARM64 processors that don’t support LSE.
+
+The Go toolchain may also generate newer instructions, but guarded by dynamic checks to ensure they’re only executed on capable processors.
+
+The `GOARM64` environment variable defaults to `v8.0`.
 
 ### ppc64 (big endian)