ARM EABI toolchain

Question

Today, I faced some weird issue with ARM toolchain EABI (cross-compiler).

Ths issue is when i try to use snwprintf() for converting floating point value to string , i was getting some junk string which does not have actual floating point value that i passed.

smaple code looke like this:

float floatValue = 1.0;
snwprintf (buffer, bufferSize, _T("%g"), floatValue);

I then debugged snwprintf and i found out that variable argument list (va_arg) is not pointing to exact data value. And by dumping the memory we were able to find the exact data present in the variable argument list. The data that should be pointed by va_arg is differing.

I don't think this is an endianess issue as integre value is working fine. The problem is only with double values.

Can anyone help me in this issue?

Answer 1

You should format/print it as a double, since floats are widened to doubles for variadic functions.

Procedure Call Standard for the ARM Architecture states following

5.5 Parameter Passing
A variadic function is always marshaled as for the base standard.

7.2 Argument Passing Conventions
For variadic functions, float arguments that match the ellipsis (…) are converted to type double.

Afaik 7.2 holds for C in general.