a24f4db2a2
To understand this change, we begin with a short description of the UIR
file format.
Every file is a header followed by a series of sections. Each section
has a kind, which determines the type of elements it contains. An
element is just a collection of one or more primitives, as defined by
package pkgbits.
Strings have their own section. Elements in the string section contain
only string primitives. To use a string, elements in other sections
encode a reference to the string section.
To illustrate, consider a simple file which exports nothing at all.
package p
In the meta section, there is an element representing a package stub.
In that package stub, a string ("p") represents both the path and name
of the package. Again, these are encoded as references.
To manage references, every element begins with a reference table.
Instead of writing the bytes for "p" directly, the package stub encodes
an index in this reference table. At that index, a pair of numbers is
stored, indicating:
1. which section
2. which element index within the section
Effectively, elements always use *2* layers of indirection; first to the
reference table, then to the bytes themselves.
With some minor hand-waving, an encoding for the above package is given
below, with (S)ections, (E)lements and (P)rimitives denoted.
+ Header
| + Section Ends // each section has 1 element
| | + 1 // String is elements [0, 1)
| | + 2 // Meta is elements [1, 2)
| + Element Ends
| | + 1 // "p" is bytes [0, 1)
| | + 6 // stub is bytes [1, 6)
+ Payload
| + (S) String
| | + (E) String
| | | + (P) String { byte } 0x70 // "p"
| + (S) Meta
| | + (E) Package Stub
| | | + Reference Table
| | | | + (P) Entry Count uvarint 1 // there is a single entry
| | | | + (P) 0th Section uvarint 0 // to String, 0th section
| | | | + (P) 0th Index uvarint 0 // to 0th element in String
| | | + Internals
| | | | + (P) Path uvarint 0 // 0th entry in table
| | | | + (P) Name uvarint 0 // 0th entry in table
Note that string elements do not have reference tables like other
elements. They behave more like a primitive.
As this is a bit complicated and getting into details of the UIR file
format, we omit some details in the documentation here. The structure
will become clearer as we continue documenting.
Change-Id: I12a5ce9a34251c5358a20f2f2c4d0f9bd497f4d0
Reviewed-on: https://go-review.googlesource.com/c/go/+/671997
Reviewed-by: Robert Griesemer <gri@google.com>
Auto-Submit: Mark Freeman <mark@golang.org>
TryBot-Bypass: Mark Freeman <mark@golang.org>
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|---|---|---|
| .github | ||
| api | ||
| doc | ||
| lib | ||
| misc | ||
| src | ||
| test | ||
| .gitattributes | ||
| .gitignore | ||
| codereview.cfg | ||
| CONTRIBUTING.md | ||
| go.env | ||
| LICENSE | ||
| PATENTS | ||
| README.md | ||
| SECURITY.md | ||
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