Hello Laura,
> We're attempting to build stable kernels with gcc9. 4.19.x fails to build with
> gcc9 as 146448524bdd ("s390/jump_label: Use "jdd" constraint on gcc9") is missing.
> This doesn't apply cleanly to 4.19.x as it needs changes from 13ddb52c165b
> ("s390/jump_label: Switch to relative references")
>
> Which is better, taking both 13ddb52c165b and 146448524bdd or doing
> a backport of 146448524bdd?
I don't know which kernel version you are referring to exactly,
however 4.19.53 from linux-stable does not contain the common code
infrastructure for relative jump labels. The infrastructure was merged
with 4.20: commit 50ff18ab497aa ("jump_label: Implement generic
support for relative references").
Therefore a backport of only 146448524bdd seems to be the way to go.
