Add new load commands

[mistydemeo]

No description provided.

[woodruffw]

This probably needs a new class, based on the corresponding structure in LLVM's Mach-O parser:

    struct build_version_command {
        uint32_t    cmd;        /* LC_BUILD_VERSION */
        uint32_t    cmdsize;    /* sizeof(struct build_version_command) plus */
        /* ntools * sizeof(struct build_tool_version) */
        uint32_t    platform;   /* platform */
        uint32_t    minos;      /* X.Y.Z is encoded in nibbles xxxx.yy.zz */
        uint32_t    sdk;        /* X.Y.Z is encoded in nibbles xxxx.yy.zz */
        uint32_t    ntools;     /* number of tool entries following this */
    };

Edit: and this structure comes along for the ride:

     struct build_tool_version {
       uint32_t tool;      // enum for the tool
       uint32_t version;   // version of the tool
  };

[woodruffw]

(For comparison, version_min_command has just two fields: version and sdk).

[mistydemeo]

Change made and tested with a binary. No build_tool_version yet.

[woodruffw]

TwoLevelHintsCommand might be a good reference for adding build_tool_version, since it encapsulates its own table/array structure.

[mistydemeo]

OK, updated. We weren't handed an offset to read the table from so I'm making the assumption here that it's the offset following view.offset + 24.

While we're not given much info about the tool structure, I am seeing what looks like correct information from what we do have:

irb(main):005:0> command.platform #=> 1, e.g. macOS
irb(main):006:0> command.minos_string #=> "10.14.0"
irb(main):007:0> command.sdk_string #=> "10.14.0"
irb(main):008:0> command.tool_entries.tools.first.tool #=> 3, e.g. ld
irb(main):009:0> command.tool_entries.tools.first.version #=> 26738945, format of this number not documented

[woodruffw]

We weren't handed an offset to read the table from so I'm making the assumption here that it's the offset following view.offset + 24.

Yeah, I think this is a reasonable assumption.

[woodruffw]

Based on http://llvm.org/doxygen/Support_2MachO_8h_source.html, this is the corresponding structure:

     struct note_command {
       uint32_t cmd;        // LC_NOTE
       uint32_t cmdsize;    // sizeof(struct note_command)
       char data_owner[16]; // owner name for this LC_NOTE
       uint64_t offset;     // file offset of this data
       uint64_t size;       // length of data region
  };

It looks like LC_NOTE is only being used in MH_CORE files, though, so this doesn't need to be implemented in this PR 🙂

[mistydemeo]

Yes, I haven't encountered it yet; I just added it since I was adding 0x32, which I have encountered. 😄

[woodruffw]

Nit: ToolEntries -> [ToolEntries] for YARD

[mistydemeo]

Fixed!

[woodruffw]

Other than that nit, this looks good to me! Thanks a ton @mistydemeo 😄

[mistydemeo]

Great! Thanks for the review. I'll merge this when CI goes green.