[PATCH] D22589: [ELF] - Introduce output section description class for holding section command

[Rui Ueyama via llvm-commits]

I don't think it would work because parsing linker scripts is not a
difficult part. That parser was not plugged into an actual logic to handle
complex linker script commands.

On Thu, Jul 21, 2016 at 2:57 AM, Sean Silva <chisophugis at gmail.com> wrote:

>
>
> On Wed, Jul 20, 2016 at 2:06 PM, Rui Ueyama via llvm-commits <
> llvm-commits at lists.llvm.org> wrote:
>
>> ruiu added inline comments.
>>
>> ================
>> Comment at: ELF/LinkerScript.h:49-59
>> @@ -48,8 +48,13 @@
>>
>> +struct OutputSectionDescription {
>> +  std::vector<StringRef> Phdrs;
>> +  std::vector<uint8_t> Filler;
>> +};
>> +
>>  struct SectionsCommand {
>>    SectionsCommandKind Kind;
>>    std::vector<StringRef> Expr;
>>    StringRef Name;
>> -  std::vector<StringRef> Phdrs;
>> +  OutputSectionDescription Section;
>>  };
>>
>> ----------------
>> I think this is towards the right direction, but it doesn't still reflect
>> the structure of SECTIONS linker script command.
>>
>> As per the linker script manual (#1), SECTIONS command contains one of
>> the following sub-commands:
>>
>>  - an ENTRY command
>>  - an overlay description
>>  - a symbol assignment
>>  - an output section description
>>
>> Since we do not support the first two, I'll ignore them in this comment.
>> So focus on the last two. We can represent the two like this.
>>
>>   enum SectionsCommandKind { AssignmentKind, DescriptionKind  };
>>
>>   struct SectionsCommand {
>>     SectionsCommandKind Kind;
>>     std::vector<StringRef> Expr;  // For AssignmentKind
>>     OutputSectionDescription Desc; // For DescriptionKind
>>   };
>>
>> The above struct doesn't have `Name` field because SECTIONS doesn't have
>> a name.
>>
>> Name is instead in output section description as described in #2. To
>> reflect that grammar, you want to define a class like this.
>>
>>   struct OutputSectionDescription {
>>     StringRef Name;
>>     std::vector<OutputSectionCommand> Commands;
>>     std::vector<uint8_t> Filler;
>>   };
>>
>> And then you want to define OutputSectionCommand to reflect
>> output-section-command as described in #2.
>>
>> So the point is to construct an AST whose structure logically matches
>> with the grammar.
>>
>
> Why don't we just bring back Rafael Auler's parser that was deleted? It
> was quite complete IIRC.
>
> -- Sean Silva
>
>
>>
>> #1 https://sourceware.org/binutils/docs/ld/SECTIONS.html#SECTIONS
>> #2 <https://sourceware.org/binutils/docs/ld/SECTIONS.html#SECTIONS%232>
>> https://sourceware.org/binutils/docs/ld/Output-Section-Description.html#Output-Section-Description
>>
>>
>> https://reviews.llvm.org/D22589
>>
>>
>>
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>>
>
>
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