Hi! As discussed in PR102024, zero width bitfields might not be the only ones causing ABI issues at least on mips, zero size arrays or (in C only) zero sized (empty) structures can be problematic too.
The following patch adds some coverage for it too. Tested on x86_64-linux with make check-gcc check-g++ RUNTESTFLAGS='ALT_CC_UNDER_TEST=gcc ALT_CXX_UNDER_TEST=g++ --target_board=unix\{-m32,-m64\} compat.exp=pr102024*' make check-gcc check-g++ RUNTESTFLAGS='ALT_CC_UNDER_TEST=clang ALT_CXX_UNDER_TEST=clang++ --target_board=unix\{-m32,-m64\} compat.exp=pr102024*' with gcc/g++ 10.3 and clang 11. Everything but (expectedly) FAIL: gcc.dg/compat/pr102024 c_compat_x_tst.o-c_compat_y_alt.o execute FAIL: gcc.dg/compat/pr102024 c_compat_x_alt.o-c_compat_y_tst.o execute for -m64 ALT_CC_UNDER_TEST=gcc passes. Ok for trunk? 2022-03-31 Jakub Jelinek <ja...@redhat.com> PR target/102024 * gcc.dg/compat/pr102024_test.h: Add further tests with zero sized structures and arrays. * g++.dg/compat/pr102024_test.h: Add further tests with zero sized arrays. --- gcc/testsuite/gcc.dg/compat/pr102024_test.h.jj 2022-03-24 12:24:41.625100842 +0100 +++ gcc/testsuite/gcc.dg/compat/pr102024_test.h 2022-03-31 17:36:33.486710917 +0200 @@ -4,3 +4,9 @@ T(2,int:0;float a;,F(2,a,2.25f,16.5f)) T(3,double a;long long:0;double b;,F(3,a,42.0,43.125)F(3,b,-17.5,35.75)) T(4,double a;long long:0;,F(4,a,1.0,17.125)) T(5,long long:0;double a;,F(5,a,2.25,16.5)) +T(6,float a;struct{}b;float c;,F(6,a,42.0f,43.125f)F(6,c,-17.5f,35.75f)) +T(7,float a;struct{}b[0];;,F(7,a,1.0f,17.125f)) +T(8,int a[0];float b;,F(8,b,2.25f,16.5f)) +T(9,double a;long long b[0];double c;,F(9,a,42.0,43.125)F(9,c,-17.5,35.75)) +T(10,double a;struct{}b;,F(10,a,1.0,17.125)) +T(11,struct{}a[0];double b;,F(11,b,2.25,16.5)) --- gcc/testsuite/g++.dg/compat/pr102024_test.h.jj 2022-03-24 12:24:41.625100842 +0100 +++ gcc/testsuite/g++.dg/compat/pr102024_test.h 2022-03-31 17:37:30.763877562 +0200 @@ -4,3 +4,9 @@ T(2,int:0;float a;,F(2,a,2.25f,16.5f)) T(3,double a;long long:0;double b;,F(3,a,42.0,43.125)F(3,b,-17.5,35.75)) T(4,double a;long long:0;,F(4,a,1.0,17.125)) T(5,long long:0;double a;,F(5,a,2.25,16.5)) +T(6,float a;struct{}b[0];float c;,F(6,a,42.0f,43.125f)F(6,c,-17.5f,35.75f)) +T(7,float a;struct{}b[0];;,F(7,a,1.0f,17.125f)) +T(8,int a[0];float b;,F(8,b,2.25f,16.5f)) +T(9,double a;long long b[0];double c;,F(9,a,42.0,43.125)F(9,c,-17.5,35.75)) +T(10,double a;struct{}b[0];,F(10,a,1.0,17.125)) +T(11,struct{}a[0];double b;,F(11,b,2.25,16.5)) Jakub