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cmd/vet: asmdecl flag scans code in multiline comments #58866

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WojciechMula opened this issue Mar 4, 2023 · 5 comments
Open

cmd/vet: asmdecl flag scans code in multiline comments #58866

WojciechMula opened this issue Mar 4, 2023 · 5 comments
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Analysis Issues related to static analysis (vet, x/tools/go/analysis) NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one.
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@WojciechMula
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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 cagedmantis changed the title cmd/vet: -asmdecl scans code in multiline comments cmd/vet: asmdecl flag scans code in multiline comments Mar 6, 2023
@cagedmantis cagedmantis added this to the Backlog milestone Mar 6, 2023
@cagedmantis cagedmantis added the NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. label Mar 6, 2023
@cagedmantis
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Please specify which is line 9.

@cagedmantis
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cc @matloob @timothy-king

@wojciech-sneller
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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
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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
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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.

@adonovan adonovan added the Analysis Issues related to static analysis (vet, x/tools/go/analysis) label Apr 23, 2023
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@cagedmantis @WojciechMula @adonovan @wojciech-sneller