cannot set breakpoint at _el2_entry when using gdb debug of bao

[xioliu]

Hello,

I am running the baremetal demo of bao, when I tried to set the breakpoint to _el2_entry or 0xfd8000000000, gdb cannot stop at the place. I found the earliest breakpoint I can set successfully is init in init.c.
Could you please give me any clue that I can debug the boot code from _el2_entry?
Thank you.

[DavidMCerdeira]

Hi,

You are not able to set the breakpoint at that point because those virtual memory memory addresses are only used starting from the init in init.c

The way to debug that code is to put a breakpoint on the physical address bao is running on.
If you are following these steps you should put a breakpoint at address 0x50000000

Let me know if this helps.

[xioliu]

Hello David,

Thank you.
I believe 0x50000000 is the address of _start in bare metal image, and yes, I can set breakpoint at 0x50000000 if I use "aarch64-none-elf-gdb baremetal.elf --tui" to debug. However, I want to debug the bao.elf and start from _el2_entry.

[xioliu]

I am wondering the reason might be, init is the earliest function gdb can find in the symbol, other functions such as boot_cache_invalidate and _el2_entry/_reset_handler are defined as NOTYPE in bao.elf.txt.

Before, _el2_entry is NOTYPE in bao.elf.txt
1307: 0000fd8000000000 0 NOTYPE GLOBAL DEFAULT 1 _el2_entry

After adding ".type _el2_entry, @function" in boot.S it changes to FUNC type, and gdb can set breakpoint on it. However there is still no source available in gdb window and dgb does not stop at _el2_entry.
1307: 0000fd8000000000 0 FUNC GLOBAL DEFAULT 1 _el2_entry

[DavidMCerdeira]

It seems we are observing different gdb behavior.

When I add the symbols with the offset right after starting gdb:

add-symbol-file bin/qemu-aarch64-virt/baremetal/bao.elf -o -FD7FB0000000
add symbol table from file "bin/qemu-aarch64-virt/baremetal/bao.elf" with all sections offset by 0xffff028050000000

I noticed the my offset value is different than yours.

When you do:

export PATH=$PATH:/home/xioliu/arm-gnu-toolchain-13.2.Rel1-x86_64-aarch64-none-elf/bin

I think you may be using the wrong gdb version.
IRC how the PATH works in the shell, you're putting that toolchain in the last place the shell checks to find a binary named aarch64-none-elf-gdb
You can try to use the absolute path or set the path as follows:

export PATH=/home/xioliu/arm-gnu-toolchain-13.2.Rel1-x86_64-aarch64-none-elf/bin:$PATH

[xioliu]

Sorry for late feedback, it has been hectic weeks.
The only aarch64-none-elf-gdb on ubuntu is under /home/xioliu/arm-gnu-toolchain-13.2.Rel1-x86_64-aarch64-none-elf/bin, so I think the PATH export is not the cause.

[DavidMCerdeira]

I just realized you are missing a minus sign when you do this:

add-symbol-file bao.elf -o 0xFD7FB0000000 

Should be:

add-symbol-file bao.elf -o -0xFD7FB0000000 

Let me know if this works

[xioliu]

@DavidMCerdeira Thank you so much David. It works.