[lldb-dev] Loadable Code Segment Information & SectionType in LLDB

[Greg Clayton via lldb-dev]

> On Aug 9, 2016, at 9:01 AM, Abhishek Aggarwal via lldb-dev <lldb-dev at lists.llvm.org> wrote:
> 
> Hello all
> 
> I have following 2 queries:
> 
> 1. Can SB APIs of LLDB provide information regarding the loadable Code Segment (r-xp part of /proc/$PID/maps file in case of Linux) of a debugged process? The information I am looking for is start address and end address of the loadable code segment of the debugged process. I know that SBModule class can provide all the Sections of the object file via SBSection class. However, I couldn't find any API in this class that can provide the information I need.

There can be many sections that contain code. I am not sure what you mean by "the loadable code segment of the debugged process". ".text" in ELF is just a section, but that doesn't mean that it will be the only section that contains code. Same goes for mach-o files. SBSection doesn't currently expose the permissions of sections, but we can easily add that since lldb_private::Section has permissions that I added about a month ago:

    //------------------------------------------------------------------
    /// Get the permissions as OR'ed bits from lldb::Permissions
    //------------------------------------------------------------------
    uint32_t
    lldb_private::Section::GetPermissions() const;

    //------------------------------------------------------------------
    /// Set the permissions using bits OR'ed from lldb::Permissions
    //------------------------------------------------------------------
    void
    lldb_private::Section::SetPermissions(uint32_t permissions);

So I would think that you would want to iterate over the sections and check their permissions and use any that are read + execute from the main executable?

> 
> 2. SBSection::GetSectionType() API returns an enum 'SectionType'. Does SectionType represent the section types as specified by different object file formats (Mach-O, PECOFF, ELF)?

It does in an agnostic way. You can watch for any sections that have eSectionTypeCode as their type from the main executable.

> 
> As an example, ELF specification specifies section types like SHT_NULL, SHT_PROGBITS, SHT_RELA, SHT_HASH, SHT_NOTE, SHT_NOBITS etc. However, SectionType enum doesn't contain all these types. Hence, enum SectionType is either a mix of all section types of different object file formats or it is a custom type of LLDB. I will appreciate any comment on this.

Again, we aren't trying to expose all of the different bits from ELF and Mach-o and COFF directly, we try to intelligently encapsulate the data by making more general definitions. If you feel that a SHT_XXX value should have its own new SectionType, we can discus that. The section type detections inside of ObjectFileELF is not that great, so feel free to improve the ObjectFileELF::CreateSections() function to "do the right thing". Anything that is SHT_PROGBITS should probably be eSectionTypeCode. It looks like just ".text" is being set to eSectionTypeCode right now.

As an example I would assume that:

SHT_NULL -> eSectionTypeOther (if this section is even exposed, and I don't believe it is)
SHT_PROGBITS -> eSectionTypeCode
SHT_RELA -> eSectionTypeELFRelocationEntries (although these definition should never have had ELF in the name, these enums are supposed to be agnostic...)
SHT_HASH -> eSectionTypeOther
SHT_NOTE -> eSectionTypeOther
SHT_NOBITS -> eSectionTypeOther
> 
> 
> Thanks
> Abhishek Aggarwal
> 
> 
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