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cmd/internal/obj: document Prog

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Change-Id: Iafc392ba06452419542ec85e91d44991839eb6f8
Reviewed-on: https://go-review.googlesource.com/19593
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>
This commit is contained in:
Michael Pratt 2016-02-17 23:06:56 -08:00 committed by Russ Cox
parent 0a55a16c91
commit ab019da727
1 changed files with 48 additions and 25 deletions
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73
src/cmd/internal/obj/link.go
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@ -203,32 +203,55 @@ const (
TYPE_REGLIST
)
// TODO(rsc): Describe prog.
// TODO(rsc): Describe TEXT/GLOBL flag in from3
// Prog describes a single machine instruction.
//
// The general instruction form is:
//
// As.Scond From, Reg, From3, To, RegTo2
//
// where As is an opcode and the others are arguments:
// From, Reg, From3 are sources, and To, RegTo2 are destinations.
// Usually, not all arguments are present.
// For example, MOVL R1, R2 encodes using only As=MOVL, From=R1, To=R2.
// The Scond field holds additional condition bits for systems (like arm)
// that have generalized conditional execution.
//
// Jump instructions use the Pcond field to point to the target instruction,
// which must be in the same linked list as the jump instruction.
//
// The Progs for a given function are arranged in a list linked through the Link field.
//
// Each Prog is charged to a specific source line in the debug information,
// specified by Lineno, an index into the line history (see LineHist).
// Every Prog has a Ctxt field that defines various context, including the current LineHist.
// Progs should be allocated using ctxt.NewProg(), not new(Prog).
//
// The other fields not yet mentioned are for use by the back ends and should
// be left zeroed by creators of Prog lists.
type Prog struct {
Ctxt *Link
Link *Prog
From Addr
From3 *Addr // optional
To Addr
Opt interface{}
Forwd *Prog
Pcond *Prog
Rel *Prog // Source of forward jumps on x86; pcrel on arm
Pc int64
Lineno int32
Spadj int32
As As // Assembler opcode.
Reg int16
RegTo2 int16 // 2nd register output operand
Mark uint16 // bitmask of arch-specific items
Optab uint16
Scond uint8
Back uint8
Ft uint8
Tt uint8
Isize uint8 // size of the instruction in bytes (x86 only)
Mode int8
Ctxt *Link // linker context
Link *Prog // next Prog in linked list
From Addr // first source operand
From3 *Addr // third source operand (second is Reg below)
To Addr // destination operand (second is RegTo2 below)
Pcond *Prog // target of conditional jump
Opt interface{} // available to optimization passes to hold per-Prog state
Forwd *Prog // for x86 back end
Rel *Prog // for x86, arm back ends
Pc int64 // for back ends or assembler: virtual or actual program counter, depending on phase
Lineno int32 // line number of this instruction
Spadj int32 // effect of instruction on stack pointer (increment or decrement amount)
As As // assembler opcode
Reg int16 // 2nd source operand
RegTo2 int16 // 2nd destination operand
Mark uint16 // bitmask of arch-specific items
Optab uint16 // arch-specific opcode index
Scond uint8 // condition bits for conditional instruction (e.g., on ARM)
Back uint8 // for x86 back end: backwards branch state
Ft uint8 // for x86 back end: type index of Prog.From
Tt uint8 // for x86 back end: type index of Prog.To
Isize uint8 // for x86 back end: size of the instruction in bytes
Mode int8 // for x86 back end: 32- or 64-bit mode
}
// From3Type returns From3.Type, or TYPE_NONE when From3 is nil.