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gccgo: bogus integer constant overflow #11525

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dvyukov opened this issue Jul 2, 2015 · 5 comments
Closed

gccgo: bogus integer constant overflow #11525

dvyukov opened this issue Jul 2, 2015 · 5 comments
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@dvyukov
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dvyukov commented Jul 2, 2015

gccgo rejects to compile the following program:

package a
var a = string(0xE000000000000000)
go.go:2:16: error: integer constant overflow

The spec says:

A constant value x can be converted to type T in any of these cases:
...
x is an integer constant and T is a string type. The same rule as for non-constant x applies in this case.
...
Converting a signed or unsigned integer value to a string type yields a string containing the UTF-8 representation of the integer. Values outside the range of valid Unicode code points are converted to "\uFFFD".

gcc version 6.0.0 2015070 (experimental) (GCC)
@dvyukov
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dvyukov commented Jul 2, 2015

@paranoiacblack

@ianlancetaylor ianlancetaylor added this to the Gccgo milestone Jul 10, 2015
@paranoiacblack
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I'm confused by this since it doesn't seem that (my versions of) either compiler accept this. The spec says this is valid if x is an integer constant and T is a string type, but x is not a valid integer constant; it overflows. I'm not sure why gccgo should compile the above program.

@ianlancetaylor
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The gc compiler also rejects this program:

foo.go:2: overflow in int -> string

I agree with Chris: I don't see why gccgo has to do anything here.

@griesemer
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@paranoiacblack This is an academic exercise at best, but the spec doesn't say that a constant argument must fit into an int (or int64). It just says that it must be an integer value, and that values outside the range result in the value "\uFFFD".

go/types accepts this without errors.

I don't think it matters much, but it seems easier to simply produce this constant string (at compile time) than reporting an error.

@gopherbot
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CL https://golang.org/cl/13906 mentions this issue.

mydongistiny pushed a commit to mydongistiny/GCC_SaberMod that referenced this issue Sep 2, 2015
compiler: Accept out of range integer -> unicode conversions.
d7739c9 
    
    When converting a signed or unsigned integer value into a constant
    string, if the integer does not fit into the Go "int" type, the string
    will become "\uFFFD."
    
    Fixes golang/go#11525.
    
    Reviewed-on: https://go-review.googlesource.com/13906


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@227395 138bc75d-0d04-0410-961f-82ee72b054a4
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