Hi.Obligatory disclaimer: building the kernel with -O3 is a non-standard thing done via this patch [1], but I've asked people in #kernelnewbies, and it was suggested that the issue should be still investigated.
So, with v5.1 kernel release I cannot build the kernel with -O3 anymore. It fails as shown below:
=== CC drivers/net/ethernet/netronome/nfp/bpf/jit.o In file included from ./include/asm-generic/bug.h:5, from ./arch/x86/include/asm/bug.h:83, from ./include/linux/bug.h:5, from drivers/net/ethernet/netronome/nfp/bpf/jit.c:6: In function ‘__emit_shf’,inlined from ‘emit_shf.constprop’ at drivers/net/ethernet/netronome/nfp/bpf/jit.c:364:2, inlined from ‘shl_reg64_lt32_low’ at drivers/net/ethernet/netronome/nfp/bpf/jit.c:379:2, inlined from ‘shl_reg’ at drivers/net/ethernet/netronome/nfp/bpf/jit.c:2506:2: ./include/linux/compiler.h:344:38: error: call to ‘__compiletime_assert_341’ declared with attribute error: BUILD_BUG_ON failed: (((0x001f0000000ULL) + (1ULL << (__builtin_ffsll(0x001f0000000ULL) - 1))) & (((0x001f0000000ULL) + (1ULL << (__builtin_ffsll(0x001f0000000ULL) - 1))) - 1)) != 0
_compiletime_assert(condition, msg, __compiletime_assert_, __LINE__) ^./include/linux/compiler.h:325:4: note: in definition of macro ‘__compiletime_assert’
prefix ## suffix(); \ ^~~~~~./include/linux/compiler.h:344:2: note: in expansion of macro ‘_compiletime_assert’
_compiletime_assert(condition, msg, __compiletime_assert_, __LINE__) ^~~~~~~~~~~~~~~~~~~./include/linux/build_bug.h:39:37: note: in expansion of macro ‘compiletime_assert’
#define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg) ^~~~~~~~~~~~~~~~~~./include/linux/bitfield.h:57:3: note: in expansion of macro ‘BUILD_BUG_ON_MSG’
BUILD_BUG_ON_MSG(__builtin_constant_p(_val) ? \ ^~~~~~~~~~~~~~~~./include/linux/bitfield.h:89:3: note: in expansion of macro ‘__BF_FIELD_CHECK’
__BF_FIELD_CHECK(_mask, 0ULL, _val, "FIELD_PREP: "); \ ^~~~~~~~~~~~~~~~drivers/net/ethernet/netronome/nfp/bpf/jit.c:341:3: note: in expansion of macro ‘FIELD_PREP’
FIELD_PREP(OP_SHF_SHIFT, shift) | ^~~~~~~~~~make[1]: *** [scripts/Makefile.build:276: drivers/net/ethernet/netronome/nfp/bpf/jit.o] Error 1 make: *** [Makefile:1726: drivers/net/ethernet/netronome/nfp/bpf/jit.o] Error 2
=== Needless to say, with -O2 this file is built just fine. My compiler is: === $ gcc --version gcc (GCC) 8.3.0 Copyright (C) 2018 Free Software Foundation, Inc.This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
=== I had no issues with -O3 before, so, maybe, this deserves a peek. I'm open to testing patches and providing more info if needed. Thanks.[1] https://gitlab.com/post-factum/pf-kernel/commit/7fef93015ff1776d08119ef3d057a9e9433954a9
-- Oleksandr Natalenko (post-factum)