Hi guys and thanks for your contributions.

I'm using uVision 1.23 with BL51 V3.70 so the features described by Jon isn't included in my version.
Next, I've check again the *.M51 file and the only way is effectively to read the last code size line and to add the length with the last starting address. It could work if there isn't any gap in the code locations between two functions.

I may build a little tool with Borland to read and convert an HEX file to a code size value. It shouldn't be so difficult.