Reading the listi contents from Dbx

Question

There is one way I can save my optimization initiation with my product. Is there any simple way to associate the register variables to the actual local variables.
In this scenario which values correspondes to "len" ....
(dbx) n
stopped in main (optimized) at line 29 in file "fileex.cc"
29 int len = ftell(myfp);
(dbx) listi
int len = ftell(myfp);
0x00010fe4: main+0x0084: call ftell [PLT] ! 0x217a8
0x00010fe8: main+0x0088: mov %l7, %o0
0x00010fec: main+0x008c: mov %o0, %i0
Thank you

Answer 1

In optimized code, there is usually no simple relationship between registers and auto variables. For example, an auto variable might be kept in one register for part of a function, and in another register elsewhere in the function -- or not in any register at all, if flow analysis can eliminate the use of the variable.
You can usually tell what is happening around a function call if you are familiar with assembler code for the platform, however. Let's consider your sample code.
On sparc, the instruction after a call or jmp is executed before the call or jmp if it is in the "delay slot". The first function parameter, if it fits in a register, is passed in register %o0. The return value of a function, if it fits in a register, is found in register %o0.
So in your example, register %i7 is passed to function ftell as the first parameter, so it corresponds to myfp. The returned value is in %o0, and is stored in len. It appears that in this section of code, len is in register %i0.