In the upcoming z (s390x) port all data symbols (i.e. global variables and constants) need to be 2-byte aligned to facilitate relative addressing. To implement this I propose:

• adding a Minalign field to complement the Maxalign field in ld.Arch
• enforcing Minalign in the symalign function in cmd/link/internal/ld/data.go

For all preexisting architectures the value of Minalign would be 1.

Other architectures could also use this property to enable some optimizations. For example on platforms where single byte loads are more expensive than n byte loads Minalign could be set to n to ensure that all global bool variables are aligned to n bytes enabling the use of n byte loads/stores.

Note: this would only apply to global variables (or constants), not struct fields or array elements. So in the following example a, b and c would all consume, and be aligned to, 2 bytes in the data section. Currently a would only consume 1 byte and all of them would be aligned to 1 byte:

package main
var a bool
var b struct { x, y bool }
var c [2]byte
...

CL to follow shortly. Currently setting Minalign to a value > 8 breaks the code that reads firstmoduledata.