On 32-bit, some DFG intrinsic getters are fallible--if the SpeculatedType does not match our expectations; however, in `ByteCodeParser::handleGetById`, we seem not to handle this possibility--the following program demonstrates this problem and crashes with a segfault on armv7:

function foo(x) {
        return x.byteLength
}

var arr = new Uint8Array(42);

var bad = {};

for (var i = 0; i < 1e6; i++) {
        if (null != foo(Object.create(bad))) {
                throw new Error();
        }
}

bad.byteLength = 42;

for (var i = 0; i < 1e6; i++) {
        if (42 != foo(arr)) {
                throw new Error();
        }
}

and in the debugger we see:

jgriego@devbox-armhf-1:~/proj/webkit$ gdb --args _build/bin/jsc test.js                                                                                                                                                                                                                    
GNU gdb (Debian 10.1-1.7) 10.1.90.20210103-git                                                                                                                                                                                                                                             
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Reading symbols from _build/bin/jsc...                                                                                                                                                                                                                                                     
(gdb) r                                                                                                                                                                                                                                                                                    
Starting program: /home/igalia/jgriego/proj/webkit/_build/bin/jsc test.js                                                                                                                                                                                                                  
[Thread debugging using libthread_db enabled]                                                                                                                                                                                                                                              
Using host libthread_db library "/lib/arm-linux-gnueabihf/libthread_db.so.1".                                                                                                                                                                                                              
[New Thread 0xf37ff440 (LWP 3086765)]                                                                                                                                                                                                                                                      
[New Thread 0xebdff440 (LWP 3086792)]
[New Thread 0xeb5fe440 (LWP 3086793)]
[New Thread 0xeadfd440 (LWP 3086794)]
[New Thread 0xea5fc440 (LWP 3086795)]
[New Thread 0xe9dfb440 (LWP 3086796)]
[New Thread 0xe95fa440 (LWP 3086797)]
[New Thread 0xe8df9440 (LWP 3086798)]

Thread 1 "jsc" received signal SIGSEGV, Segmentation fault.
0xf5c67fc8 in WTF::Vector<JSC::CallVariant, 1u, WTF::CrashOnOverflow, 16u, WTF::FastMalloc>::size (this=0x0) at /home/igalia/jgriego/proj/webkit/_build/WTF/Headers/wtf/Vector.h:764
764         size_t size() const { return m_size; }
(gdb) bt
#0  0xf5c67fc8 in WTF::Vector<JSC::CallVariant, 1u, WTF::CrashOnOverflow, 16u, WTF::FastMalloc>::size (this=0x0) at /home/igalia/jgriego/proj/webkit/_build/WTF/Headers/wtf/Vector.h:764
#1  0xf5c67f58 in WTF::Vector<JSC::CallVariant, 1u, WTF::CrashOnOverflow, 16u, WTF::FastMalloc>::Vector (this=0xfffe9a2c, other=...) at /home/igalia/jgriego/proj/webkit/_build/WTF/Headers/wtf/Vector.h:964
#2  0xf5c64e38 in JSC::CallLinkStatus::CallLinkStatus (this=0xfffe9a2c) at /home/igalia/jgriego/proj/webkit/Source/JavaScriptCore/bytecode/CallLinkStatus.h:44
#3  0xf5e5306a in JSC::DFG::ByteCodeParser::handleGetById (this=0xfffed32c, destination=..., prediction=2207613190144, base=0xf2e81ba0, identifier=..., identifierNumber=0, getByStatus=..., type=JSC::AccessType::GetById, osrExitIndex=...)
    at /home/igalia/jgriego/proj/webkit/Source/JavaScriptCore/dfg/DFGByteCodeParser.cpp:4818
#4  0xf5ed5d56 in JSC::DFG::ByteCodeParser::parseGetById<JSC::OpGetById> (this=0xfffed32c, currentInstruction=0xf2eb44b7) at /home/igalia/jgriego/proj/webkit/Source/JavaScriptCore/dfg/DFGByteCodeParser.cpp:5374
#5  0xf5e6061a in JSC::DFG::ByteCodeParser::parseBlock (this=0xfffed32c, limit=14) at /home/igalia/jgriego/proj/webkit/Source/JavaScriptCore/dfg/DFGByteCodeParser.cpp:6580
#6  0xf5e741a6 in JSC::DFG::ByteCodeParser::parseCodeBlock (this=0xfffed32c) at /home/igalia/jgriego/proj/webkit/Source/JavaScriptCore/dfg/DFGByteCodeParser.cpp:8844
#7  0xf5e746d6 in JSC::DFG::ByteCodeParser::parse (this=0xfffed32c) at /home/igalia/jgriego/proj/webkit/Source/JavaScriptCore/dfg/DFGByteCodeParser.cpp:9046
#8  0xf5e75266 in JSC::DFG::parse (graph=...) at /home/igalia/jgriego/proj/webkit/Source/JavaScriptCore/dfg/DFGByteCodeParser.cpp:9182
#9  0xf60ae650 in JSC::DFG::Plan::compileInThreadImpl (this=0xf2ea12f0) at /home/igalia/jgriego/proj/webkit/Source/JavaScriptCore/dfg/DFGPlan.cpp:201
#10 0xf66829a8 in JSC::JITPlan::compileInThread (this=0xf2ea12f0, thread=0x0) at /home/igalia/jgriego/proj/webkit/Source/JavaScriptCore/jit/JITPlan.cpp:172
#11 0xf6720b00 in JSC::JITWorklist::enqueue (this=0xf2ec5288, plan=...) at /home/igalia/jgriego/proj/webkit/Source/JavaScriptCore/jit/JITWorklist.cpp:84
#12 0xf5fc08e0 in JSC::DFG::compileImpl (vm=..., codeBlock=0xf06afdc0, profiledDFGCodeBlock=0x0, mode=JSC::JITCompilationMode::DFG, osrEntryBytecodeIndex=..., mustHandleValues=..., callback=...) at /home/igalia/jgriego/proj/webkit/Source/JavaScriptCore/dfg/DFGDriver.cpp:90
#13 0xf5fc09ac in JSC::DFG::compile (vm=..., codeBlock=0xf06afdc0, profiledDFGCodeBlock=0x0, mode=JSC::JITCompilationMode::DFG, osrEntryBytecodeIndex=..., mustHandleValues=..., callback=...) at /home/igalia/jgriego/proj/webkit/Source/JavaScriptCore/dfg/DFGDriver.cpp:106
#14 0xf667a7d6 in JSC::operationOptimize (vmPointer=0xf0cf5000, bytecodeIndexBits=0) at /home/igalia/jgriego/proj/webkit/Source/JavaScriptCore/jit/JITOperations.cpp:2028
#15 0xf0dff87a in ?? ()
Backtrace stopped: previous frame identical to this frame (corrupt stack?)
(gdb) frame 3
#3  0xf5e5306a in JSC::DFG::ByteCodeParser::handleGetById (this=0xfffed32c, destination=..., prediction=2207613190144, base=0xf2e81ba0, identifier=..., identifierNumber=0, getByStatus=..., type=JSC::AccessType::GetById, osrExitIndex=...)
    at /home/igalia/jgriego/proj/webkit/Source/JavaScriptCore/dfg/DFGByteCodeParser.cpp:4818
4818            getter, numberOfParameters - 1, registerOffset, *variant.callLinkStatus(), prediction);
(gdb) p variant.callLinkStatus()
$1 = (JSC::CallLinkStatus *) 0x0
(gdb) p/x prediction
$2 = 0x20200000000
(gdb) p variant.intrinsic()
[Thread 0xebdff440 (LWP 3086792) exited]
[Thread 0xea5fc440 (LWP 3086795) exited]
$3 = JSC::TypedArrayByteLengthIntrinsic

* * *

To fix, I propose we add code to generate an ordinary GetById node if the code generation for the intrinsic fails; I'll send a patch to this effect shortly.