reflectx

Golang reflect package hack tools

Go Version

• Go 1.21 ~ 1.27

Compilers

• Go (gc)
• LLGo

Platforms

• macOS
• Linux
• Windows
• WebAssembly

Go ABI

• ABI0 stack-based ABI
• ABIInternal register-based Go calling convention proposal
  • Go1.21+: amd64 arm64 ppc64/ppc64le riscv64
  • Go1.23+: amd64 arm64 ppc64/ppc64le riscv64 loong64

Field

• reflectx.CanSet
• reflectx.Field
• reflectx.FieldByIndex
• reflectx.FieldByName
• reflectx.FieldByNameFunc

Named

• reflectx.StructOf
• reflectx.NamedTypeOf
• reflectx.SetUnderlying
• reflectx.SetTypeName

Method

• reflectx.Method

• reflectx.MakeMethod

• reflectx.NewMethodSet

• reflectx.SetMethodSet

• reflectx.StructToMethodSet

Interface

• reflectx.InterfaceOf
• reflectx.NamedInterfaceOf
• reflectx.NewInterfaceType
• reflectx.SetInterfaceType

Context

• reflectx.NewContext

Method allocs (icall)

Default gc path: each installed method needs a unique ifn stub.

• allocs

import _ "github.com/goplus/reflectx/icall/icall[N]"

• install icall_gen

go install github.com/goplus/reflectx/cmd/icall_gen@latest

icall_gen -o icall1024.go -pkg main -size 1024

ifacefuncval (optional)

Alternative to icall: methods share makeFuncStub instead of an icall stub table. reflectx stores an untagged *makeFuncImpl in addReflectOff and sets tflagIfaceFuncval (1<<6). A patched runtime tags itab.Fun (makeFuncImpl*|1) so interface calls unwrap.

Needs a patched Go 1.25.x, 1.26.x, or 1.27.x and an explicit tag. Supported GOARCH: wasm, arm64, amd64, 386.

• install iface_patch

go install github.com/goplus/reflectx/cmd/iface_patch@latest

iface_patch /path/to/go   # 1.25.x, 1.26.x, or 1.27.x
cd /path/to/go/src && ./make.bash
export GOROOT=/path/to/go
export PATH="$GOROOT/bin:$PATH"
go test -tags goplus.ifacefuncval .
# wasip1: GOOS=wasip1 GOARCH=wasm go test -exec wasmtime -tags goplus.ifacefuncval .

Without the tag, a patched compiler matches official gc. An unpatched compiler still accepts the tag; interface method calls then trap.

You can export GOFLAGS='-tags=goplus.ifacefuncval', or prefix a command: GOFLAGS='-tags=goplus.ifacefuncval' go build (also go run / go test).

See cmd/iface_patch/README.md.

build linkname mode

go build -tags linknamefix -ldflags="-checklinkname=0"