wa-lang.org/wazero@v1.0.2/internal/asm/impl.go (about)

     1  package asm
     2  
     3  import (
     4  	"encoding/binary"
     5  	"fmt"
     6  )
     7  
     8  // BaseAssemblerImpl includes code common to all architectures.
     9  //
    10  // Note: When possible, add code here instead of in architecture-specific files to reduce drift:
    11  // As this is internal, exporting symbols only to reduce duplication is ok.
    12  type BaseAssemblerImpl struct {
    13  	// SetBranchTargetOnNextNodes holds branch kind instructions (BR, conditional BR, etc.)
    14  	// where we want to set the next coming instruction as the destination of these BR instructions.
    15  	SetBranchTargetOnNextNodes []Node
    16  
    17  	// OnGenerateCallbacks holds the callbacks which are called after generating native code.
    18  	OnGenerateCallbacks []func(code []byte) error
    19  }
    20  
    21  // SetJumpTargetOnNext implements AssemblerBase.SetJumpTargetOnNext
    22  func (a *BaseAssemblerImpl) SetJumpTargetOnNext(nodes ...Node) {
    23  	a.SetBranchTargetOnNextNodes = append(a.SetBranchTargetOnNextNodes, nodes...)
    24  }
    25  
    26  // AddOnGenerateCallBack implements AssemblerBase.AddOnGenerateCallBack
    27  func (a *BaseAssemblerImpl) AddOnGenerateCallBack(cb func([]byte) error) {
    28  	a.OnGenerateCallbacks = append(a.OnGenerateCallbacks, cb)
    29  }
    30  
    31  // BuildJumpTable implements AssemblerBase.BuildJumpTable
    32  func (a *BaseAssemblerImpl) BuildJumpTable(table *StaticConst, labelInitialInstructions []Node) {
    33  	a.AddOnGenerateCallBack(func(code []byte) error {
    34  		// Compile the offset table for each target.
    35  		base := labelInitialInstructions[0].OffsetInBinary()
    36  		for i, nop := range labelInitialInstructions {
    37  			if nop.OffsetInBinary()-base >= JumpTableMaximumOffset {
    38  				return fmt.Errorf("too large br_table")
    39  			}
    40  			// We store the offset from the beginning of the L0's initial instruction.
    41  			binary.LittleEndian.PutUint32(code[table.offsetInBinary+uint64(i*4):table.offsetInBinary+uint64((i+1)*4)],
    42  				uint32(nop.OffsetInBinary())-uint32(base))
    43  		}
    44  		return nil
    45  	})
    46  }