On Monday, June 29, 2020 at 8:16:14 PM UTC-5 Ian Lance Taylor wrote:
> On Mon, Jun 29, 2020 at 5:32 PM Bill Morgan > <arthurwil...@gmail.com> wrote: > > > > for this code: > > > > m := make(map[int]int, 9) > > > > I think the compiler creates a maptype that is stored at > type.*+60480(SB) that it uses for the call to runtime.makemap: > > > > m := make(map[int]int, 9) > > 0x10d0b81 488d05f8ec0000 LEAQ type.*+60480(SB), AX > > 0x10d0b88 48890424 MOVQ AX, 0(SP) > > 0x10d0b8c 48c744240809000000 MOVQ $0x9, 0x8(SP) > > 0x10d0b95 48c744241000000000 MOVQ $0x0, 0x10(SP) > > 0x10d0b9e 6690 NOPW > > 0x10d0ba0 e8fbdff3ff CALL runtime.makemap(SB) > > > > Where is the code in the compiler that creates the maptype? I'm > wondering how the bucket size is computed and how the rest of the maptype > structure is filled out. > > https://golang.org/src/cmd/compile/internal/gc/reflect.go#L189 > > > Is there a way to print out the type info stored in the binary? > > I'm not sure if this is what you want, but you can use reflect.TypeOf: > https://play.golang.org/p/FEUIoqc6SMU . > > Ian > Thanks Ian, that is pretty cool. I think that is printing out the map[int]int type though instead of the *maptype that is generated by the compiler and passed to runtime.makemap. I think this is loading a pointer to a maptype into AX to pass as the first arg to runtime.makemap. The maptype seems to be stored at type.*+60480(SB). LEAQ type.*+60480(SB), AX here's the type I'm asking about: where is this guy created in the compiler? type maptype struct { typ _type key *_type elem *_type bucket *_type // internal type representing a hash bucket // function for hashing keys (ptr to key, seed) -> hash hasher func(unsafe.Pointer, uintptr) uintptr keysize uint8 // size of key slot elemsize uint8 // size of elem slot bucketsize uint16 // size of bucket flags uint32 } Here are the runtime.makemap comments and signature // makemap implements Go map creation for make(map[k]v, hint). // If the compiler has determined that the map or the first bucket // can be created on the stack, h and/or bucket may be non-nil. // If h != nil, the map can be created directly in h. // If h.buckets != nil, bucket pointed to can be used as the first bucket. func makemap(t *maptype, hint int, h *hmap) *hmap { -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/c99ffa05-5c22-416c-bef9-f871490eff2an%40googlegroups.com.
