Huh... I don't know much about the GCC ABI, could you enlighten me as to why this doesn't apply to us?

My understanding is that this is just a warning not to link objects compiled with pre- and post-7.1 together.

EDIT: this seems to confirm that: https://stackoverflow.com/q/52020305/8342274

We use -Wno-psabi in CI, and I use it for my arm binaries.

My understanding is that this is just a warning not to link objects compiled with pre- and post-7.1 together.

Correct. It doesn't apply to us while building the distribution binaries because we use the same C and C++ compilers for everything including the dependencies.

ACK 1edddf5

Ah! In that case, ACK 5016091

It's a bit annoying that there doesn't seem to be a way to suppress these warnings with any sort of granularity, and the only option is disabling ABI warnings wholesale. Although I'm wondering if this is some buggy behaviour in GCC?

Ideally we could just tell GCC that we don't care about ABI related warnings for any ABI changes that happened before GCC 8.5 (i.e ABI version 13, from G++ 8.2), given that's what we are using to compile all code for the arm-linux-gnueabihf target.

I took a minified test case from the bug in question:

#include <stdarg.h>

template <int N> struct A { double p; };

A<0> v;

template <int N> struct B {
	typedef A<N> T;
	int i, j;
};

int fn1(int a, B<0> b) {
	return a + b.i;
}

int main() {
	return 0;
}

which produces the warning we're seeing:

# arm-linux-gnueabihf-g++ --version
# arm-linux-gnueabihf-g++ (Ubuntu 9.3.0-17ubuntu1~20.04) 9.3.0

arm-linux-gnueabihf-g++ abi.cpp -std=c++17

abi.cpp: In function ‘int fn1(int, B<0>)’:
abi.cpp:12:5: note: parameter passing for argument of type ‘B<0>’ changed in GCC 7.1
   12 | int fn1(int a, B<0> b) {
      |     ^~~

I assumed with some combination of the -Wabi=X or -fabi-(compat)-version=X options you'd be able to suppress the warning output, but I can't find a combination that works.

Note that if you compile with -Wabi (these warnings are emitted regardless), GCC tells you that it wont warn about anything, unless you've set a -fabi-version= to something other than the default (0 or 13 in our case), but still warns:

arm-linux-gnueabihf-g++ abi.cpp -std=c++17 -Wabi
cc1plus: warning: ‘-Wabi’ won’t warn about anything [-Wabi]
cc1plus: note: ‘-Wabi’ warns about differences from the most up-to-date ABI, which is also used by default
cc1plus: note: use e.g. ‘-Wabi=11’ to warn about changes from GCC 7
abi.cpp: In function ‘int fn1(int, B<0>)’:
abi.cpp:12:5: note: parameter passing for argument of type ‘B<0>’ changed in GCC 7.1
   12 | int fn1(int a, B<0> b) {
      |     ^~~

If you set -fabi-verison=12 (G++ 8.0), GCC no longer tells you that it won't warn, but it still emits the warnings about changes in GCC 7.1:

arm-linux-gnueabihf-g++ abi.cpp -std=c++17 -fabi-version=12
abi.cpp: In function ‘int fn1(int, B<0>)’:
abi.cpp:12:5: note: parameter passing for argument of type ‘B<0>’ changed in GCC 7.1
   12 | int fn1(int a, B<0> b) {
      |     ^~~

If you set -Wabi=12, same deal:

arm-linux-gnueabihf-g++ abi.cpp -std=c++17 -Wabi=12
abi.cpp: In function ‘int fn1(int, B<0>)’:
abi.cpp:12:5: note: parameter passing for argument of type ‘B<0>’ changed in GCC 7.1
   12 | int fn1(int a, B<0> b) {
      |     ^~~

🤷

Is it possible that ABI and psABI are two independent settings, and that psABI doesn't have this kind of granular versioning?

Is it possible that ABI and psABI are two independent settings, and that psABI doesn't have this kind of granular versioning?

Yea that may be the case. Also, as of GCC 11.1, the -Wpsabi remain undocumented:

g++-11 --help=warnings | grep -i abi
  -Wabi                       Warn about things that will change when compiling with an ABI-compliant compiler.
  -Wabi-tag                   Warn if a subobject has an abi_tag attribute that the complete object type does not have.
  -Wabi=                      Warn about things that change between the current -fabi-version and the specified version.
  -Wpsabi                     This option lacks documentation.

Could be good to add one line explaining that this is disabled to suppress uncontrollable warning output, but should be ok to do based on us consistently using GCC 8.5 for the Guix build.

Guix builds

@fanquake Actually, is there a reason for us to even care about the ABI/psABI at all (in guix builds, at least)? We control the entire build environment, so whatever is used, it will be consistent for everything in the build?