gun global compat cscope do not "support cs find a" , which means: Find assignments to this symbol

[??????]

gun global compat cscope do not "support cs find a" , which means: Find assignments to this symbol

• What is your environment (OS)? ---------------ubuntu 16.04
• Which version of GLOBAL are you using? --gtags (GNU GLOBAL) 6.6.2
• What did you do? (command line) --------------cs find a xxx
• What did you expect from it?        ---------------result as cscope, 
• What was occurred? (as is)           ----------------always no result

ps: For example, test at linux kernel code tree,

if use cscope database, then do command: cs f a early_boot_irqs_disabled

will show result:

Cscope tag: early_boot_irqs_disabled

   #   line  filename / context / line

   1    519  /home/zhl/mycode/linux_kernel_learn/init/main.c <<start_kernel>>

             early_boot_irqs_disabled = true;

   2    598  /home/zhl/mycode/linux_kernel_learn/init/main.c <<start_kernel>>

             early_boot_irqs_disabled = false;

but when use gtags-cscope compat mode, then do command: cs f a early_boot_irqs_disabled

E259: no matches found for cscope query a early_boot_irqs_disabled of early_boot_irqs_disabled