read_sysreg(TTBR_EL2) not work in linux, but read_sysreg(CurrentEL) works. (arm64)

[Chan Kim]

When running u-boot starting linux on qemu and using gdb to debug the program, (on a modified arm64 virt machine),

I see this strange things.

Right after I enter linux start_kernel( ), I added these two lines,

datax = read_sysreg(CurrentEL);    -- line 1

datax = read_sysreg(TTBR1_EL2);    -- line 2

after line 1 and before line 2, the value of datax is seen as 8. (bit [3:2] is current EL, so it's EL2). 

after line 2, the value of datax is still 8, but the result of `info reg TTBR1_EL2` is 0x8065a000.

The disassembled assembly code shows no reading of TTBR1_EL2 register.

How can this happen? Should I set something in the kernel configuration?

Any help will be really appreciated.

Thank you!

Chan Kim