cmd/vet: asmdecl flag scans code in multiline comments

[WojciechMula]

What version of Go are you using (go version)?

$ go version
go version go1.20 linux/amd64

What did you do?

This is the repro:

~/tmp/govet$ cat go.mod 
module main

~/tmp/govet$ cat main.go 
package main

// go:noescape
// go:nosplit
func procedure()

func main() {
    procedure()
}

~/tmp/govet$ cat proc_amd64.s 
#include "textflag.h"
#include "funcdata.h"
#include "go_asm.h"

TEXT ·procedure(SB), NOSPLIT|NOFRAME, $0-0
    /*
        Commented out garbage

        MOVQ    nonexistingprocedureargument+42(FP), ZMM1
    */
    RET

# this compiles correctly
~/tmp/govet$ go build; echo $?
0

# vet complains
~/tmp/govet$ go vet -asmdecl
# main
./proc_amd64.s:9:1: [amd64] procedure: unknown variable nonexistingprocedureargument

When line 9 is commented with // then go vet does not complain.

[cagedmantis]

Please specify which is line 9.

[cagedmantis]

cc @matloob @timothy-king

[wojciech-sneller]

Please specify which is line 9.

That's the number from the quoted output:

~/tmp/govet$ go vet -asmdecl
# main
./proc_amd64.s:9:1: [amd64] procedure: unknown variable nonexistingprocedureargument

[wojciech-sneller]

I looked briefly at x/tools/go/analysis/passes/asmdecl/asmdecl.go, there's a custom, primitive parser. It does not interpret macros, ifdefs, includes, etc.

Example of an other problem:

#define ARG_X_OFS 12345 // silly offset
...
MOVQ x+ARG_X_OFS(FP), AX

Go vet won't complain.

asmdecl has to use the cmd/asm lexer (src/cmd/asm/internal/lex/). Fixing anything in the current parser is possible but IMO makes no sense.

[WojciechMula]

I was thinking about that issue and the conclusion is: this behaviour should be only documented. go vet has to be fast and pulling a fully-fledged parser only to point out issues in the functionality used by a few people makes no sense.