a bug in genksysms/CONFIG_MODVERSIONS w/ __attribute__((foo))?

From: Nick Desaulniers
Date: Mon Aug 26 2019 - 17:22:43 EST

I'm looking into a linkage failure for one of our device kernels, and
it seems that genksyms isn't producing a hash value correctly for
aggregate definitions that contain __attribute__s like

$ echo 'struct foo { int bar; };' | ./scripts/genksyms/genksyms -d
Defn for struct foo == <struct foo { int bar ; } >
Hash table occupancy 1/4096 = 0.000244141
$ echo 'struct __attribute__((packed)) foo { int bar; };' |
./scripts/genksyms/genksyms -d
Hash table occupancy 0/4096 = 0

I assume the __attribute__ part isn't being parsed correctly (looks
like genksyms is a lex/yacc based C parser).

The issue we have in our out of tree driver (*sadface*) is basically a
EXPORT_SYMBOL'd function whose signature contains a packed struct.

Theoretically, there should be nothing wrong with exporting a function
that requires packed structs, and this is just a bug in the lex/yacc
based parser, right? I assume that not having CONFIG_MODVERSIONS
coverage of packed structs in particular could lead to potentially
not-fun bugs? Or is using packed structs in exported function symbols
with CONFIG_MODVERSIONS forbidden in some documentation somewhere I
~Nick Desaulniers