Bug 1739321 Comment 4 Edit History

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Original comment by
on 
The clang bugtracker is down right now since they're in the middle of a failing migration to github. But to record some info:

The DWARF info for the .o file that is relevant to `JSString` contains:
```
<1><48cbf>: Abbrev Number: 43 (DW_TAG_class_type)
    <48cc0>   DW_AT_calling_convention: 4       (pass by ref)
    <48cc1>   DW_AT_name        : (indirect string, offset: 0x6830): JSLinearString
    <48cc5>   DW_AT_byte_size   : 24
    <48cc6>   DW_AT_decl_file   : 25
    <48cc7>   DW_AT_decl_line   : 788
 <2><48cc9>: Abbrev Number: 5 (DW_TAG_inheritance)
    <48cca>   DW_AT_type        : <0x4862b>
    <48cce>   DW_AT_data_member_location: 0
    <48ccf>   DW_AT_accessibility: 1    (public)
    ...
```

so a complete declaration of `JSLinearString`. It is tagged as inheriting from 0x4862b, which is:
```
 <1><4862b>: Abbrev Number: 19 (DW_TAG_class_type)
    <4862c>   DW_AT_name        : (indirect string, offset: 0x44c1): JSString
    <48630>   DW_AT_declaration : 1
 <2><48630>: Abbrev Number: 20 (DW_TAG_subprogram)
    <48631>   DW_AT_linkage_name: (indirect string, offset: 0x2b059): _ZN8JSString23fillWithRepresentativesEP9JSContextN2JS6HandleIPN2js11ArrayObjectEEE
    <48635>   DW_AT_name        : (indirect string, offset: 0x2b0ac): fillWithRepresentatives
    <48639>   DW_AT_decl_file   : 25
    ...
```

Now, I don't know how to read DWARF, but the `DW_AT_declaration` makes it look to me like it's doing a forward/partial declaration of the `JSString` type and not the type itself -- and yet, it's also enumerating fields of it. Which seems a bit weird, but I think the DWARF format version 5 spec says it's ok in section E.2.3.

I have no clue why clang is not emitting the complete declaration of `JSString`. Hopefully I can remember to file a bug once it's possible again.
Revision 1 by
on 
The clang bugtracker is down right now since they're in the middle of a failing migration to github. But to record some info:

The DWARF info for the .o file that is relevant to `JSString` contains:
```
<1><48cbf>: Abbrev Number: 43 (DW_TAG_class_type)
    <48cc0>   DW_AT_calling_convention: 4       (pass by ref)
    <48cc1>   DW_AT_name        : (indirect string, offset: 0x6830): JSLinearString
    <48cc5>   DW_AT_byte_size   : 24
    <48cc6>   DW_AT_decl_file   : 25
    <48cc7>   DW_AT_decl_line   : 788
 <2><48cc9>: Abbrev Number: 5 (DW_TAG_inheritance)
    <48cca>   DW_AT_type        : <0x4862b>
    <48cce>   DW_AT_data_member_location: 0
    <48ccf>   DW_AT_accessibility: 1    (public)
    ...
```

so a complete declaration of `JSLinearString`. It is tagged as inheriting from 0x4862b, which is:
```
 <1><4862b>: Abbrev Number: 19 (DW_TAG_class_type)
    <4862c>   DW_AT_name        : (indirect string, offset: 0x44c1): JSString
    <48630>   DW_AT_declaration : 1
 <2><48630>: Abbrev Number: 20 (DW_TAG_subprogram)
    <48631>   DW_AT_linkage_name: (indirect string, offset: 0x2b059): _ZN8JSString23fillWithRepresentativesEP9JSContextN2JS6HandleIPN2js11ArrayObjectEEE
    <48635>   DW_AT_name        : (indirect string, offset: 0x2b0ac): fillWithRepresentatives
    <48639>   DW_AT_decl_file   : 25
    ...
```

Now, I don't know how to read DWARF, but the `DW_AT_declaration` makes it look to me like it's doing a forward/partial declaration of the `JSString` type and not the type itself -- and yet, it's also enumerating fields of it. Which seems a bit weird, but I think the DWARF format version 5 spec says it's ok in section E.2.3.

I have no clue why clang is not emitting the defining declaration of `JSString`. Hopefully I can remember to file a bug once it's possible again.
Revision 2 by
on 
The clang bugtracker is down right now since they're in the middle of a failing migration to github. But to record some info:

The DWARF info for the .o file that is relevant to `JSString` contains:
```
<1><48cbf>: Abbrev Number: 43 (DW_TAG_class_type)
    <48cc0>   DW_AT_calling_convention: 4       (pass by ref)
    <48cc1>   DW_AT_name        : (indirect string, offset: 0x6830): JSLinearString
    <48cc5>   DW_AT_byte_size   : 24
    <48cc6>   DW_AT_decl_file   : 25
    <48cc7>   DW_AT_decl_line   : 788
 <2><48cc9>: Abbrev Number: 5 (DW_TAG_inheritance)
    <48cca>   DW_AT_type        : <0x4862b>
    <48cce>   DW_AT_data_member_location: 0
    <48ccf>   DW_AT_accessibility: 1    (public)
    ...
```

so a complete declaration of `JSLinearString`. It is tagged as inheriting from 0x4862b, which is:
```
 <1><4862b>: Abbrev Number: 19 (DW_TAG_class_type)
    <4862c>   DW_AT_name        : (indirect string, offset: 0x44c1): JSString
    <48630>   DW_AT_declaration : 1
 <2><48630>: Abbrev Number: 20 (DW_TAG_subprogram)
    <48631>   DW_AT_linkage_name: (indirect string, offset: 0x2b059): _ZN8JSString23fillWithRepresentativesEP9JSContextN2JS6HandleIPN2js11ArrayObjectEEE
    <48635>   DW_AT_name        : (indirect string, offset: 0x2b0ac): fillWithRepresentatives
    <48639>   DW_AT_decl_file   : 25
    ...
```

Now, I don't know how to read DWARF, but the `DW_AT_declaration` makes it look to me like it's doing only a non-defining (forward? partial?) declaration of the `JSString` type -- and yet, it's also enumerating fields of it. Which seems a bit weird, but I think the DWARF format version 5 spec says it's ok in section E.2.3.

I have no clue why clang is not emitting the defining declaration of `JSString`. Hopefully I can remember to file a bug once it's possible again.

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