[lldb-dev] IRInterpreter strange behavior
Sean Callanan
scallanan at apple.com
Thu Jun 26 16:47:54 PDT 2014
Zachary,
LLI’s interpreter is (a) not really supported code, having been superseded by the JIT; and (b) founded on the assumption that we’re interpreting inside the current process.
The LLDB IRInterpreter is focused on interpreting in the context of another process (the IRMemoryMap is the interface it uses).
It’s not clear to me what’s doing this. On OS X we don’t get this error:
–
(lldb) expr const unsigned int $foo = 5
(lldb) expr &$foo
(const unsigned int *) $0 = 0x046cdbe26a5d1000
–
and the symbol isn’t there either:
–
; ModuleID = '$__lldb_module'
target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-apple-macosx"
; Function Attrs: nounwind
define void @"_Z12$__lldb_exprPv"(i8* %"$__lldb_arg") #0 {
%1 = getelementptr i8* %"$__lldb_arg", i32 8
%2 = bitcast i8* %1 to i32**
%3 = getelementptr i8* %"$__lldb_arg", i32 0
%4 = bitcast i8* %3 to i32***
%5 = load i32*** %4
%6 = alloca i8*, align 8, !clang.decl.ptr !8
store i8* %"$__lldb_arg", i8** %6, align 8
%7 = icmp eq i8 0, 0
br i1 %7, label %8, label %10
; <label>:8 ; preds = %0
%9 = load i32** %2, align 8
store i32* %9, i32** %5, align 8
br label %10
; <label>:10 ; preds = %8, %0
ret void
}
–
What’s producing that? Is it some kind of guard variable? (IRForTarget.cpp strips those, but only the ones I’ve seen…)
Sean
> On Jun 26, 2014, at 4:34 PM, Zachary Turner <zturner at google.com> wrote:
>
> I'm trying to diagnose a problem with the IRInterpreter, but this is all very foreign to me so I think I should ask here.
>
> Before I go into the details though, a simple question which I don't want to get lost in the shuffle: Why doesn't LLDB use LLI instead of creating its own interpreter?
>
> Anyway, on to the problem. First of all, this is only on Windows. This all just works on Linux and presumably Mac, although I don't have a Mac to test. The scenario is this: I run the following two commands:
>
> (lldb) expr const unsigned int $foo = 5
> (lldb) expr &$foo
>
> And this results in an error. Printing the value of $foo works fine, it just can't get the address.
>
> I turn on logging and I see this:
>
> Module as passed in to IRInterpreter::Interpret:
> "; ModuleID = '$__lldb_module'
> target datalayout = "e-m:w-p:32:32-i64:64-f80:32-n8:16:32-S32"
> target triple = "i686-pc-windows-msvc"
>
> @"\01?$S1@?0??$__lldb_expr@@YAXPAX at Z@4IA" = internal global i32 0
>
> ; Function Attrs: nounwind
> define void @"\01?$__lldb_expr@@YAXPAX at Z"(i8* %"$__lldb_arg") #0 {
> %1 = getelementptr i8* %"$__lldb_arg", i32 8
> %2 = bitcast i8* %1 to i32**
> %3 = getelementptr i8* %"$__lldb_arg", i32 0
> %4 = bitcast i8* %3 to i32***
> %5 = load i32*** %4
> %6 = alloca i8*, align 4, !clang.decl.ptr !8
> store i8* %"$__lldb_arg", i8** %6, align 4
> %7 = load i32* @"\01?$S1@?0??$__lldb_expr@@YAXPAX at Z@4IA"
> %8 = and i32 %7, 1
> %9 = icmp ne i32 %8, 0
> br i1 %9, label %13, label %10
>
> ; <label>:10 ; preds = %0
> %11 = or i32 %7, 1
> store i32 %11, i32* @"\01?$S1@?0??$__lldb_expr@@YAXPAX at Z@4IA"
> %12 = load i32** %2, align 4
> store i32* %12, i32** %5, align 4
> br label %13
>
> ; <label>:13 ; preds = %10, %0
> ret void
> }
>
> attributes #0 = { nounwind "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "no-realign-stack" "stack-protector-buffer-size"="0" "unsafe-fp-math"="false" "use-soft-float"="false" }
>
> !clang.global.decl.ptrs = !{!0, !1, !2, !0, !0}
> !llvm.module.flags = !{!3, !4, !5, !6}
> !llvm.ident = !{!7}
>
> !0 = metadata !{null, i64 7787680}
> !1 = metadata !{null, i64 7787504}
> !2 = metadata !{void (i8*)* @"\01?$__lldb_expr@@YAXPAX at Z", i64 7787328}
> !3 = metadata !{i32 1, metadata !"Objective-C Version", i32 2}
> !4 = metadata !{i32 1, metadata !"Objective-C Image Info Version", i32 0}
> !5 = metadata !{i32 1, metadata !"Objective-C Image Info Section", metadata !"__DATA, __objc_imageinfo, regular, no_dead_strip"}
> !6 = metadata !{i32 4, metadata !"Objective-C Garbage Collection", i32 0}
> !7 = metadata !{metadata !"clang version 3.5.0 "}
> !8 = metadata !{i64 7787200}
> "
> IRMemoryMap::WriteMemory (0x81ffc, 0x124db54, 0x4) went to [0x2000..0x82000)
> Made an allocation for argument i8* %"$__lldb_arg"
> Data region : 1000
> Ref region : 81ffc
> Interpreting %1 = getelementptr i8* %"$__lldb_arg", i32 8
> IRMemoryMap::WriteMemory (0x81ff8, 0x702b00, 0x4) went to [0x2000..0x82000)
> Interpreted a GetElementPtrInst
> P : i8* %"$__lldb_arg" 0x81ffc
> Poffset : %1 = getelementptr i8* %"$__lldb_arg", i32 8 0x81ff8
> Interpreting %2 = bitcast i8* %1 to i32**
> IRMemoryMap::WriteMemory (0x81ff4, 0x702b00, 0x4) went to [0x2000..0x82000)
> Interpreting %3 = getelementptr i8* %"$__lldb_arg", i32 0
> IRMemoryMap::WriteMemory (0x81ff0, 0x702b00, 0x4) went to [0x2000..0x82000)
> Interpreted a GetElementPtrInst
> P : i8* %"$__lldb_arg" 0x81ffc
> Poffset : %3 = getelementptr i8* %"$__lldb_arg", i32 0 0x81ff0
> Interpreting %4 = bitcast i8* %3 to i32***
> IRMemoryMap::WriteMemory (0x81fec, 0x702b00, 0x4) went to [0x2000..0x82000)
> Interpreting %5 = load i32*** %4
> IRMemoryMap::ReadMemory (0x81fec, 0x702b00, 0x4) came from [0x2000..0x82000)
> IRMemoryMap::ReadMemory (0x1000, 0x702b00, 0x4) came from [0x1000..0x1010)
> IRMemoryMap::WriteMemory (0x81fe8, 0x702b00, 0x4) went to [0x2000..0x82000)
> Interpreted a LoadInst
> P : 0x81fec
> R : 0x1000
> D : 0x81fe8
> Interpreting %6 = alloca i8*, align 4, !clang.decl.ptr !8
> IRMemoryMap::WriteMemory (0x81fe0, 0x124dc00, 0x4) went to [0x2000..0x82000)
> Interpreted an AllocaInst
> R : 0x81fe4
> P : 0x81fe0
> Interpreting store i8* %"$__lldb_arg", i8** %6, align 4
> IRMemoryMap::ReadMemory (0x81fe0, 0x702b00, 0x4) came from [0x2000..0x82000)
> IRMemoryMap::ReadMemory (0x81ffc, 0x702b00, 0x4) came from [0x2000..0x82000)
> IRMemoryMap::WriteMemory (0x81fe4, 0x702b00, 0x4) went to [0x2000..0x82000)
> Interpreted a StoreInst
> D : 0x81ffc
> P : 0x81fe0
> R : 0x81fe4
> Interpreting %7 = load i32* @"\01?$S1@?0??$__lldb_expr@@YAXPAX at Z@4IA"
> LoadInst's pointer doesn't resolve to anything
>
> I've bolded a few of the relevant lines. I'm not really sure what's going on here, or even how to diagnose it. Can anyone offer some advice?
>
> Thanks
>
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> lldb-dev at cs.uiuc.edu
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