To clarify, for those listening at home, it was the second UB (overflow) that exposed a real bug. Type punning was innocuous here, but given it's technically UB, I fixed it anyway.
On Tue, Feb 5, 2019 at 9:33 AM Davide Italiano <dccitali...@gmail.com> wrote: > > Shafik, Zachary, I think you reported this a bit ago, but now I got > around to fix it (also because it was breaking something real). > > Thanks, > > -- > Davide > > On Tue, Feb 5, 2019 at 9:30 AM Davide Italiano via lldb-commits > <lldb-commits@lists.llvm.org> wrote: > > > > Author: davide > > Date: Tue Feb 5 09:30:53 2019 > > New Revision: 353191 > > > > URL: http://llvm.org/viewvc/llvm-project?rev=353191&view=rev > > Log: > > [Obj-C] Fix undefined behaviour(s) in the new NSTaggedDate formatter. > > > > Type punning through a union -> no good. > > double to uint64 to double again -> no good either. > > > > The nice side effect, other than silencing the sanitizer bot > > is that it fixes the formatting of some dates, e.g. Jan 1st 1970. > > > > <rdar://problem/47617983> > > > > Modified: > > lldb/trunk/source/Plugins/Language/ObjC/Cocoa.cpp > > > > Modified: lldb/trunk/source/Plugins/Language/ObjC/Cocoa.cpp > > URL: > > http://llvm.org/viewvc/llvm-project/lldb/trunk/source/Plugins/Language/ObjC/Cocoa.cpp?rev=353191&r1=353190&r2=353191&view=diff > > ============================================================================== > > --- lldb/trunk/source/Plugins/Language/ObjC/Cocoa.cpp (original) > > +++ lldb/trunk/source/Plugins/Language/ObjC/Cocoa.cpp Tue Feb 5 09:30:53 > > 2019 > > @@ -27,6 +27,7 @@ > > #include "lldb/Utility/Stream.h" > > > > #include "llvm/ADT/APInt.h" > > +#include "llvm/ADT/bit.h" > > > > #include "Plugins/LanguageRuntime/ObjC/AppleObjCRuntime/AppleObjCRuntime.h" > > > > @@ -749,24 +750,18 @@ bool lldb_private::formatters::NSURLSumm > > /// distantFuture, except within about 1e-25 second of the reference > > date. > > const int TAGGED_DATE_EXPONENT_BIAS = 0x3ef; > > > > -typedef union { > > - struct { > > - uint64_t fraction:52; // unsigned > > - uint64_t exponent:11; // signed > > - uint64_t sign:1; > > - } repr; > > - uint64_t i; > > - double d; > > -} DoubleBits; > > -typedef union { > > - struct { > > - uint64_t fraction:52; // unsigned > > - uint64_t exponent:7; // signed > > - uint64_t sign:1; > > - uint64_t unused:4; // placeholder for pointer tag bits > > - } repr; > > - uint64_t i; > > -} TaggedDoubleBits; > > +struct DoubleBits { > > + uint64_t fraction : 52; // unsigned > > + uint64_t exponent : 11; // signed > > + uint64_t sign : 1; > > +}; > > + > > +struct TaggedDoubleBits { > > + uint64_t fraction : 52; // unsigned > > + uint64_t exponent : 7; // signed > > + uint64_t sign : 1; > > + uint64_t unused : 4; // placeholder for pointer tag bits > > +}; > > > > static uint64_t decodeExponent(uint64_t exp) { > > // Tagged exponent field is 7-bit signed. Sign-extend the value to 64 > > bits > > @@ -774,24 +769,24 @@ static uint64_t decodeExponent(uint64_t > > return llvm::SignExtend64<7>(exp) + TAGGED_DATE_EXPONENT_BIAS; > > } > > > > -static uint64_t decodeTaggedTimeInterval(uint64_t encodedTimeInterval) { > > +static double decodeTaggedTimeInterval(uint64_t encodedTimeInterval) { > > if (encodedTimeInterval == 0) > > return 0.0; > > if (encodedTimeInterval == std::numeric_limits<uint64_t>::max()) > > return (uint64_t)-0.0; > > > > - TaggedDoubleBits encodedBits = {}; > > - encodedBits.i = encodedTimeInterval; > > - DoubleBits decodedBits; > > + TaggedDoubleBits encodedBits = > > + llvm::bit_cast<TaggedDoubleBits>(encodedTimeInterval); > > + assert(encodedBits.unused == 0); > > > > // Sign and fraction are represented exactly. > > // Exponent is encoded. > > - assert(encodedBits.repr.unused == 0); > > - decodedBits.repr.sign = encodedBits.repr.sign; > > - decodedBits.repr.fraction = encodedBits.repr.fraction; > > - decodedBits.repr.exponent = decodeExponent(encodedBits.repr.exponent); > > + DoubleBits decodedBits; > > + decodedBits.sign = encodedBits.sign; > > + decodedBits.fraction = encodedBits.fraction; > > + decodedBits.exponent = decodeExponent(encodedBits.exponent); > > > > - return decodedBits.d; > > + return llvm::bit_cast<double>(decodedBits); > > } > > > > bool lldb_private::formatters::NSDateSummaryProvider( > > @@ -868,7 +863,8 @@ bool lldb_private::formatters::NSDateSum > > > > // Accomodate for the __NSTaggedDate format introduced in Foundation > > 1600. > > if (class_name == g___NSTaggedDate) { > > - auto *runtime = > > llvm::dyn_cast_or_null<AppleObjCRuntime>(process_sp->GetObjCLanguageRuntime()); > > + auto *runtime = llvm::dyn_cast_or_null<AppleObjCRuntime>( > > + process_sp->GetObjCLanguageRuntime()); > > if (runtime && runtime->GetFoundationVersion() >= 1600) > > date_value = decodeTaggedTimeInterval(value_bits << 4); > > } > > > > > > _______________________________________________ > > lldb-commits mailing list > > lldb-commits@lists.llvm.org > > https://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-commits _______________________________________________ lldb-commits mailing list lldb-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-commits
