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cmd/internal/obj/arm: Wrong SWI/SWPW/SWPBU in ARM assembler #20375

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benshi001 opened this issue May 16, 2017 · 4 comments
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cmd/internal/obj/arm: Wrong SWI/SWPW/SWPBU in ARM assembler #20375

benshi001 opened this issue May 16, 2017 · 4 comments
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Go1.10

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@benshi001
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  1. SWPBU/SWPW

The assembler front end expects SWPW/SWPBU in
SWPBU R4, (R2), R8
Otherwise it will complaint
SWPBU: expected register; found (R2)

But it I add a new line in cmd/asm/internal/asm/testdata/arm.s
endtoend_test.go:155: mismatched output:
have 00725 (testdata/arm.s:1001) SWPBU (R2), R4, R8
want 00725 (testdata/arm.s:1001) SWPBU R4, (R2), R8

  1. SWI
    According to the newest ARM maunal,
    SWI only has one form
    SWI $imm
    But
    SWI (R0) is also accepted, which should be rejected.
@benshi001
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benshi001 commented May 16, 2017 •
edited

  1. SWPW/SWPBU can be fixed by changing either the front end, line 555 - 566 of cmd/asm/internal/asm/asm.go
    case sys.ARM:
    // Special cases.
    if arch.IsARMSTREX(op) {
    /*
    STREX x, (y), z
    from=(y) reg=x to=z
    */
    prog.From = a[1]
    prog.Reg = p.getRegister(prog, op, &a[0])
    prog.To = a[2]
    break
    }

or the backend line 219 of cmd/internal/obj/arm/asm5.go
{ASWPW, C_SOREG, C_REG, C_REG, 40, 4, 0, 0, 0},
which one is better?

  1. no "SWI (Reg)" is used in the entire go source tree, so we can safely remove line 130 of cmd/internal/obj/arm/asm5.go

    {ASWI, C_NONE, C_NONE, C_LOREG, 10, 4, 0, 0, 0},

@benshi001
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"SWI.S $3" is also accepted, but SWI does not has a S bit.

@benshi001
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There is a "STREX R3, (R1), R0" in runtime/internal/atomic/asm_arm.s, and
"{ASTREXD, C_SOREG, C_REG, C_REG, 92, 4, 0, 0, 0}," in cmd/internal/obj/arm/asm5.go,
so the least change way might be changing cmd/asm/internal/asm/testdata/arm.s,
SWPW R3, (R7), R9 // SWPW (R7), R3, R9 // 939007e1
SWPBU R4, (R2), R8 // SWPBU (R2), R4, R8 // 948042e1

@benshi001 benshi001 changed the title Wrong SWI/SWPW/SWPBU in ARM assembler cmd/internal/obj/arm: Wrong SWI/SWPW/SWPBU in ARM assembler May 16, 2017
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CL https://golang.org/cl/43552 mentions this issue.

@cherrymui cherrymui added this to the Go1.10 milestone May 16, 2017
@golang golang locked and limited conversation to collaborators May 18, 2018
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