It is not safe to assume that you can just take any source code written for one compiler and have it produce identical reults on another!

This is especially so for the likes of Keil, which have a very great number of "special features" to tune them specifically to a limited architecture like the 8051.

No doubt SDCC also has its own set of "special features" and tricks to tune it specifically to a limited architecture like the 8051 - but the chances that these are idetical to Keil's (or any other's) is slim in the extreme!

For a start, are you certain that your SDCC startup code is correct?

Then, take a look at your 'C' source and search for anywhere that relies upon anything specific to Keil; eg,

data representation (size, endianness, etc);

function calling conventions (parameter passing, return values, etc);

any specific language extensions...

SDCC has a bug on it or i make sth wrong?

You said this is your "first time [with] SDCC", so the chances are high that it's not an SDCC bug...

You'd probably be better off starting with SDCC examples until you're familiar with how SDCC works; porting between different compilers requires that you are familiar with both of them!