aleksandr.urakov added inline comments.
================
Comment at: lit/SymbolFile/PDB/Inputs/ClassLayoutTest.cpp:37
+ };
+ union { // Test unnamed union. MSVC treats it as `int a; float b;`
+ int a;
----------------
aleksandr.urakov wrote:
> aleksandr.urakov wrote:
> > Hui wrote:
> > > aleksandr.urakov wrote:
> > > > Here is a problem. `MicrosoftRecordLayoutBuilder` asserts every field
> > > > or base offset, but in our case fields `a` and `b` are treated as
> > > > `struct Complex`'s fields, not `union`'s, so lldb crashes in debug on
> > > > this. I can't find enough info in PDB to restore the unnamed union
> > > > here. Do you have any ideas about it?
> > >
> > > Based on MSVC cl yielded PDB, you could have full information to restore
> > > the unnamed UDT.
> > >
> > > From my experience, PDB yielded by clang-cl (/Z7 or /Zi) is slightly
> > > different from the one by cl.
> > >
> > > Both contain information about forwarded unnamed UDT.
> > > However PDB yielded by clang-cl more or less lacks the member
> > > information. See below.
> > >
> > > The CodeView info is good. Maybe you need to look at LLC?
> > >
> > > CodeView
> > >
> > > ```
> > > FieldList (0x1044) {
> > > TypeLeafKind: LF_FIELDLIST (0x1203)
> > > DataMember {
> > > TypeLeafKind: LF_MEMBER (0x150D)
> > > AccessSpecifier: Public (0x3)
> > > Type: int (0x74)
> > > FieldOffset: 0x0
> > > Name: a
> > > }
> > > DataMember {
> > > TypeLeafKind: LF_MEMBER (0x150D)
> > > AccessSpecifier: Public (0x3)
> > > Type: float (0x40)
> > > FieldOffset: 0x0
> > > Name: b
> > > }
> > > }
> > >
> > > Union (0x1045) {
> > > TypeLeafKind: LF_UNION (0x1506)
> > > MemberCount: 2
> > > Properties [ (0x608)
> > > HasUniqueName (0x200)
> > > Nested (0x8)
> > > Sealed (0x400)
> > > ]
> > > FieldList: <field list> (0x1044)
> > > SizeOf: 4
> > > Name: Complex::<unnamed-tag>
> > > LinkageName: .?AT<unnamed-type-$S2>@Complex@@
> > > }
> > >
> > > ```
> > >
> > > llvm-pdbutil pdb (clang-cl /z7)
> > >
> > > (found unnamed symbol, however size = 0, they will be just ignored. See
> > > PDBASTParser.cpp #259
> > > The size should not be zero)
> > >
> > >
> > > ```
> > > struct Complex::<unnamed-tag> [sizeof = 0] {}
> > >
> > > union Complex::<unnamed-tag> [sizeof = 0] {}
> > >
> > > struct Complex [sizeof = 728] {
> > > data +0x00 [sizeof=720] _List* array[90]
> > > data +0x2d0 [sizeof=4] int x
> > > data +0x2d4 [sizeof=4] int a
> > > data +0x2d4 [sizeof=4] float b
> > > }
> > >
> > > ```
> > >
> > > llvm-pdbutil pdb ( cl /z7)
> > >
> > > ( you have full information to restore unnamed)
> > > ```
> > >
> > > struct Complex [sizeof = 728] {
> > > data +0x00 [sizeof=720] _List* array[90]
> > > data +0x2d0 [sizeof=4] int x
> > > data +0x2d4 [sizeof=4] int a
> > > data +0x2d4 [sizeof=4] float b
> > > }
> > >
> > > Total padding 3 bytes (25% of class size)
> > > Immediate padding 3 bytes (25% of class size)
> > >
> > > struct Complex::<unnamed-tag> [sizeof = 4] {
> > > data +0x00 [sizeof=4] int x
> > > }
> > >
> > > union Complex::<unnamed-tag> [sizeof = 4] {
> > > data +0x00 [sizeof=4] int a
> > > data +0x00 [sizeof=4] float b
> > > }
> > > ```
> > >
> > >
> > Thank you! But what means `LLC`?
> I have figured that out, sorry. I usually use disassembly tools for this
> purpose.
I have just dumped two PDBs, one was produced with `cl` and `link`, and other
with `clang-cl` and `lld-link` with the same keys (`/Zi /GS- /c` for
compilation, `/nodefaultlib /debug:full /entry:main` for linking). I have
compiled the source:
```
struct S {
struct {
char a;
short b;
};
short c;
union {
short d;
int e;
};
};
int main() {
S ss[sizeof(S)];
return 0;
}
```
and have retrieved identical type infos from PDBs:
```
struct S::<unnamed-tag> [sizeof = 0] {}
union S::<unnamed-tag> [sizeof = 0] {}
struct S [sizeof = 12] {
data +0x00 [sizeof=1] char a
<padding> (1 bytes)
data +0x02 [sizeof=2] short b
data +0x04 [sizeof=2] short c
<padding> (2 bytes)
data +0x08 [sizeof=2] short d
data +0x08 [sizeof=4] int e
}
Total padding 3 bytes (25% of class size)
Immediate padding 3 bytes (25% of class size)
struct S::<unnamed-tag> [sizeof = 4] {
data +0x00 [sizeof=1] char a
<padding> (1 bytes)
data +0x02 [sizeof=2] short b
}
Total padding 1 bytes (25% of class size)
Immediate padding 1 bytes (25% of class size)
union S::<unnamed-tag> [sizeof = 4] {
data +0x00 [sizeof=2] short d
data +0x00 [sizeof=4] int e
}
```
So it seems that both `cl` and `clang` emit enough info to restore the layout
of unnamed unions or structs. But we also need to:
- Find a location of unnamed fields of such types in the outer structure (`S`
in our case);
- Somehow drop fields `a`, `b`, `d` and `e` from it (because we will place the
unnamed fields of the unnamed types there).
And I can't find enough info for that. How do you think, is it possible?
https://reviews.llvm.org/D49410
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