In forward slice, how to handle STORE Pcode whose target is the global variable area?

[Kalvin2077]

Hi!

I'm writing a headless script about forward slice, but it doesn't handle global variables very well.

These codes are from GUI ghidra. I noticed the symbol (line) of the destination (global variable) has been shown. If I double-click the line, the listing view can jump to the address of line.

08003fc4 53 54           strb       r3,[r2,r1]=>line                                 = ??
                                 (unique, 0x96900, 4) = INT_ADD (register, 0x28, 4), (register, 0x24, 4)
                                 (unique, 0xc7780, 1) = SUBPIECE (register, 0x2c, 4), (const, 0x0, 4)
                                 STORE (const, 0x1a1, 8), (unique, 0x96900, 4), (unique, 0xc7780, 1)

I thought I could use related methods to find ram varnode about global variable by symbol. Then I tried to get symbols for each inputs varnode, but I got the following logs:

[pcodeOp@08003fc4]  ---  STORE (const, 0x1a1, 4) , (unique, 0x98300, 4) , (register, 0x20, 1)  
Not found symbol for varnode: (const, 0x1a1, 4)  
Not found symbol for varnode: (unique, 0x98300, 4)  
Not found symbol for varnode: (register, 0x20, 1)  

I guess there is some pre-processing in GUI Ghidra, maybe backforward slice, to infer the symbol line.
I have tried to find it in source code, but I have no direction.

Or should I manually implement a backward slice to find the ram varnode of the global variable?

This is a screenshot of the GUI Ghidra: