Debugging Code Generation in Go

Transcript

1. Debugging Code
   Generation in Go
   Jaana B. Dogan, Google
   jbd@google.com
   

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4. @rakyll
   Who needs this talk?
   ● Developers who want to debug the compilation.
   ● Reverse engineers, security practitioners, ...
   ● Current or prospective Go contributors.
   ● Anyone who wants to study compilers.
   

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5. Lexing and parsing
   Transformations on AST
   SSA optimizations
   

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6. main program
   package main
   import "fmt"
   func main() {
   sum := 1 + 1
   fmt.Printf("sum: %v\n", sum)
   }
   

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7. main program
   $ go build -x
   WORK=/var/folders/zq/wgh6df4s6fz2wjwdp5dvzlww005d
   21/T/go-build399551378
   mkdir -p $WORK/b001/
   cat >$WORK/b001/importcfg.link << 'EOF' #
   internal
   packagefile
   github.com/rakyll/codegen=/Users/jbd/Library/Cach
   es/go-build/00/00ed60989b390a64bad3cb01d4ec61aae6
   d0ea61e3e38fc35052d1ab5b0efe66-d
   packagefile ...
   

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8. main program
   $ go build -n # run dry
   WORK=/var/folders/zq/wgh6df4s6fz2wjwdp5dvzlww005d
   21/T/go-build399551378
   mkdir -p $WORK/b001/
   cat >$WORK/b001/importcfg.link << 'EOF' #
   internal
   packagefile
   github.com/rakyll/codegen=/Users/jbd/Library/Cach
   es/go-build/00/00ed60989b390a64bad3cb01d4ec61aae6
   d0ea61e3e38fc35052d1ab5b0efe66-d
   packagefile ...
   

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9. main program
   $ go build -a # build without the cache
   

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10. main program
    $ go build -work # don’t delete work directory
    WORK=/var/folders/zq/wgh6df4s6fz2wjwdp5dvzlww005d
    21/T/go-build444532126
    

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11. main program
    $ go list -f {{.GoFiles}} # investigate files
    [main.go]
    $ GOOS=windows go list -f {{.GoFiles}}
    [main.go main_windows.go]
    See https://golang.org/pkg/cmd/go/internal/list/ for more.
    

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12. main program
    $ go build -gcflags="-S" # print Go assembly
    # github.com/rakyll/codegen
    os.(*File).close STEXT dupok nosplit size=26
    args=0x18 locals=0x0
    0x0000 00000 (:1) TEXT
    os.(*File).close(SB), DUPOK|NOSPLIT|ABIInternal,
    $0-24
    0x0000 00000 (:1) FUNCDATA$0,
    gclocals·e6397a44f8e1b6e77d0f200b4fba5269(SB)
    0x0000 00000 (:1) FUNCDATA...
    

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13. main program
    $ go tool objdump -s main.main
    TEXT main.main(SB)
    /Users/jbd/go/src/github.com/rakyll/codegen/main.
    go
    main.go:5 0x109adc0 65488b0c2530000000
    MOVQ GS:0x30, CX
    main.go:5 0x109adc9 483b6110 CMPQ
    0x10(CX), SP
    main.go:5 0x109adcd 0f8690000000
    JBE 0x109ae63
    main.go:5 0x109add3 4883ec68 SUBQ ...
    

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14. main program
    $ go tool nm | grep runtime.walltime
    1044b20 T runtime.walltime
    1054c50 T runtime.walltime_trampoline
    

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15. main program
    $ go build -gcflags="-N" # disable optimizations
    $ go build -gcflags="-l" # disable inlining
    $ go build -gcflags="-N -l" # disable both
    

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16. main program
    $ GOSSAFUNC=main go build && open ssa.html
    

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17. main program
    $ go build -gcflags="-m" # escape analysis
    $ go build -gcflags="-m=2" # more info
    

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18. main program
    $ go build -gcflags="-live" # debug liveness
    $ go build -gcflags="-live=2" # more info
    

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19. main program
    $ go build -gcflags="-bench=bench.out"
    $ go build -gcflags="-race" # race detector
    $ go build -gcflags="-memprofile=profile.out"
    $ go build -gcflags="-traceprofile=trace.out"
    # ...
    

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20. Thanks.
    Jaana B. Dogan, Google
    jbd@google.com
    

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