potential runtime problem on arm, powerpc and s390 due to incorrect assumption on char signedness
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as already discussed on debian-devel, I would like to draw your attention
to a potential runtime problem for each package on arm, powerpc and s390.
As I experienced, a lot of people assume that char is signed per default.
This is _not_ true on arm, powerpc and s390.
The following explanation of a typical problem can be found at
>>The following code fragment will ignore the end-of-file when char is
>>implemented using unsigned char, due to internal conversions between data
>> char c;
>> while ((c = getchar()) != EOF)
>> process character in c
>>EOF is usually -1. When getchar() returns a -1, that value immediately goes
>>into an instance of type plain char, c. If plain char is not signed, then
>>an internal conversion copies the low-order bits of -1 into c; now c is 255.
>>Moreover, EOF, which is signed, finds itself to be the right hand operand
>>in a mixed-mode expression involving an unsigned operand. In this case,
>>the signed value is raised to an unsigned value; -1 now becomes 65,535.
>>Finally, 255 is never equal to 65,535; the relational test is always true;
>>and the EOF is ignored. The correction is to make the type of variable c
In other contexts the right solution is to make the type of the variable
In most cases the compiler will issue one of the following warnings:
comparison is always true due to limited range of data type
comparison is always false due to limited range of data type
comparison of unsigned expression >= 0 is always true
initialization of negative value \`-1' to \`char'
pointer targets in assignment differ in signedness
pointer targets in passing arg 1 of \`...' differ in signedness
Please check the build log of your package on one of the platforms mentioned
above for the warnings.
A not complete list of packages that have got this problem ordered by package
owner can be found at
The build logs of these packages are at http://buildd.debian.org or at
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