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Message-ID: <20200707160528.GA1300535@google.com> Date: Tue, 7 Jul 2020 09:05:28 -0700 From: Sami Tolvanen <samitolvanen@...gle.com> To: Masahiro Yamada <masahiroy@...nel.org>, Jakub Kicinski <kuba@...nel.org> Cc: Will Deacon <will@...nel.org>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, "Paul E. McKenney" <paulmck@...nel.org>, Kees Cook <keescook@...omium.org>, Nick Desaulniers <ndesaulniers@...gle.com>, clang-built-linux <clang-built-linux@...glegroups.com>, Kernel Hardening <kernel-hardening@...ts.openwall.com>, linux-arch <linux-arch@...r.kernel.org>, linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>, Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, linux-pci@...r.kernel.org, X86 ML <x86@...nel.org> Subject: Re: [PATCH 00/22] add support for Clang LTO On Tue, Jul 07, 2020 at 08:51:07AM -0700, Sami Tolvanen wrote: > After spending some time debugging this with Nick, it looks like the > error is caused by a recent optimization change in LLVM, which together > with the inlining of ur_load_imm_any into jeq_imm, changes a runtime > check in FIELD_FIT that would always fail, to a compile-time check that > breaks the build. In jeq_imm, we have: > > /* struct bpf_insn: _s32 imm */ > u64 imm = insn->imm; /* sign extend */ > ... > if (imm >> 32) { /* non-zero only if insn->imm is negative */ > /* inlined from ur_load_imm_any */ > u32 __imm = imm >> 32; /* therefore, always 0xffffffff */ > > /* > * __imm has a value known at compile-time, which means > * __builtin_constant_p(__imm) is true and we end up with > * essentially this in __BF_FIELD_CHECK: > */ > if (__builtin_constant_p(__imm) && __imm <= 255) Should be __imm > 255, of course, which means the compiler will generate a call to __compiletime_assert. > Jiong, Jakub, do you see any issues here? (Jiong's email bounced, so removing from the recipient list.) Sami
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