Date: Mon, 28 Dec 2015 12:55:24 +0000 From: bugzilla-noreply@freebsd.org To: freebsd-bugs@FreeBSD.org Subject: [Bug 205663] clang++ 3.7.1 gets Bus Errors during compilation on arm that has SCTLR bit[1]==1 (alignment required) Message-ID: <bug-205663-8@https.bugs.freebsd.org/bugzilla/>
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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D205663 Bug ID: 205663 Summary: clang++ 3.7.1 gets Bus Errors during compilation on arm that has SCTLR bit[1]=3D=3D1 (alignment required) Product: Base System Version: 11.0-CURRENT Hardware: arm OS: Any Status: New Severity: Affects Many People Priority: --- Component: bin Assignee: freebsd-bugs@FreeBSD.org Reporter: markmi@dsl-only.net # more /tmp/main-5dac8d.cpp # 1 "<built-in>" # 1 "main.cc" template <class _Tp, class _Up> struct __has_rebind { template <class _Xp> static char __test(typename _Xp::template rebind<_= Up>* =3D 0); }; int main () { return 0; } # more /tmp/main-5dac8d.sh # Crash reproducer for FreeBSD clang version 3.7.1 (tags/RELEASE_371/final 255217) 20151225 # Driver args: "--driver-mode=3Dg++" "main.cc" # Original command: "/usr/bin/clang++" "-cc1" "-triple" "armv6k--freebsd11.0-gnueabi" "-emit-obj" "-mrelax-all" "-disable-free" "-main-file-name" "main.cc" "-mrelocation-model" "static" "-mthread-model" "posix" "-mdisable-fp-elim" "-masm-verbose" "-mconstructor-aliases" "-target-cpu" "arm1176jzf-s" "-target-feature" "+soft-float" "-target-featu= re" "+soft-float-abi" "-target-feature" "-neon" "-target-feature" "-crypto" "-target-abi" "aapcs-linux" "-msoft-float" "-mfloat-abi" "soft" "-dwarf-column-info" "-resource-dir" "/usr/bin/../lib/clang/3.7.1" "-internal-isystem" "/usr/include/c++/v1" "-fdeprecated-macro" "-fdebug-compilation-dir" "/root/c_tests" "-ferror-limit" "19" "-fmessage-length" "338" "-mstackrealign" "-fno-signed-char" "-fobjc-runtime=3Dgnustep" "-fcxx-exceptions" "-fexceptions" "-fdiagnostics-show-option" "-fcolor-diagnostics" "-o" "/tmp/main-e20b38.o" "-x" "c++" "main.cc" "/usr/bin/clang++" "-cc1" "-triple" "armv6k--freebsd11.0-gnueabi" "-emit-o= bj" "-mrelax-all" "-disable-free" "-main-file-name" "main.cc" "-mrelocation-mod= el" "static" "-mthread-model" "posix" "-mdisable-fp-elim" "-masm-verbose" "-mconstructor-aliases" "-target-cpu" "arm1176jzf-s" "-target-feature" "+soft-float" "-target-feature" "+soft-float-abi" "-target-feature" "-neon" "-target-feature" "-crypto" "-target-abi" "aapcs-linux" "-msoft-float" "-mfloat-abi" "soft" "-dwarf-column-info" "-fdeprecated-macro" "-ferror-lim= it" "19" "-fmessage-length" "338" "-mstackrealign" "-fno-signed-char" "-fobjc-runtime=3Dgnustep" "-fcxx-exceptions" "-fexceptions" "-fdiagnostics-show-option" "-fcolor-diagnostics" "-x" "c++" "main-5dac8d.c= pp" The code involved is from lib/AST/Type.cpp : DependentTemplateSpecializationType::DependentTemplateSpecializationType( ElaboratedTypeKeyword Keyword, NestedNameSpecifier *NNS, const IdentifierInfo *Nam= e, unsigned NumArgs, const TemplateArgument *Args, QualType Canon) : TypeWithKeyword(Keyword, DependentTemplateSpecialization, Canon, true, t= rue, /*VariablyModified=3D*/false, NNS && NNS->containsUnexpandedParameterPack()), NNS(NNS), Name(Name), NumArgs(NumArgs) { assert((!NNS || NNS->isDependent()) && "DependentTemplateSpecializatonType requires dependent qualifier"); for (unsigned I =3D 0; I !=3D NumArgs; ++I) { if (Args[I].containsUnexpandedParameterPack()) setContainsUnexpandedParameterPack(); new (&getArgBuffer()[I]) TemplateArgument(Args[I]); } } The failing code is for the "placement new" in the loop: A) &getArgBuffer()[I] is not always an address for which the vst1.64 instruction gets an aligned address. but. . . B) TemplateArgument(Args[I])'s copy construction activity has code (such as= the vst1.64) requiring a specific alignment when SCTLR bit[1]=3D=3D1. C) Nothing here has any explicitly packed data structures. As for (A): class DependentTemplateSpecializationType : public TypeWithKeyword, public llvm::FoldingSetNode { . . . const TemplateArgument *getArgBuffer() const { return reinterpret_cast<const TemplateArgument*>(this+1); } TemplateArgument *getArgBuffer() { return reinterpret_cast<TemplateArgument*>(this+1); } clang++ is over-allocating the space for the DependentTemplateSpecializationType objects and using the extra space that = is afterwards to hold (a somewhat C-style array of) TemplateArgument instances. But the logic for this does nothing explicit about alignment of the TemplateArgument instance pointers, not even partially via explicitly controlling sizeof(DependentTemplateSpecializationType). sizeof(TemplateArgument) also needs to be controlled in order to have the notation &getArgBuffer()[I] maintain alignment in its results when &getArgBuffer()[0] is well aligned. The existing code does not explicitly force any specific minimum TemplateArgument alignment, other than 1. (Implicit ABI rules might get some alignment --if some of those rules are being applied. Separately there is the issue that the code produced did not treat the poin= ters returned from getArgBuffer() methods as "opaque pointer" examples but they = are. Having compiled with -fmax-type-align=3D4 the code should have not have req= uired 8 byte alignment (vst1.64). It should have produced code that required 4 (o= r 2 or 1). Quoting for -fmax-type-align=3D?: Instruct the code generator to not enforce a higher alignment than the given number (of bytes) when accessing memory via an opaque pointer or reference Those pointers certainly are opaque and should be treated as such. The "reinterpret_cast" use is a big clue that clang++ should respect. In other words: I see two clang++ defects in the overall evidence, one of w= hich directly leads to the Bus Errors being possible. --=20 You are receiving this mail because: You are the assignee for the bug.=
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