1. Article Purpose[edit source]
This article explains how to debug TF-A firmware.
Debug is specifically linked to the TrustZone environment.
There are two main ways to debug TF-A, using traces inside the code, or by using JTAG to access the secure world. The focus here is on the solution integrated in OpenSTLinux: debug over gdb (ST-Link or JTAG based)
2. Debugging[edit source]
2.1. TF-A Version number[edit source]
The starting point for debugging is to identify the TF-A version used in the target. Debug and release versions are displayed on the console with the following format:
NOTICE: BL2: v2.0(debug):<tag>
- v2.0 is the TF-A version used.
- (debug) : Build mode enable
- <tag> : Git reference resulting from the git describe command at build time
2.2. Debug with traces[edit source]
TF-A allows RELEASE and DEBUG modes to be enabled:
- RELEASE mode builds with default LOG_LEVEL to 20, which only prints ERROR and NOTICE traces
- DEBUG mode enables the -g build flag (for debug build object), and defaults LOG_LEVEL to 40
With the debug LOG_LEVEL, you can add console traces such as ERROR, NOTICE, WARNING or INFO. Please refer to include/common/debug.h.
For both modes, you must ensure that the UART is properly configured:
- BL2: UART traces are enabled by default
- BL32: UART traces are enabled by default
Traces and errors are available on the console defined in the chosen node of the device tree by the stdout-path property:
chosen {
stdout-path = "serial0:115200n8";
};
2.3. Debug with GDB[edit source]
TF-A runs in SYSRAM and is executed in CPU secure state. One can debug TF-A through JTAG using an ST-Link or the JTAG output, depending on the board.
2.3.1. Debug boot sequence[edit source]
The BL2 boot stage is only executed during a boot sequence. To break into BL2, connect to the target and break.
Load symbols to the correct offset:
(gdb) add-symbol-file <path_to_build_folder>/tf-a-bl2.elf (or bl2.elf) <load_address>
BL2 and BL32 load addresses can be found in the generated tf-a-stm32mp157c-<board>.map file:
...
*fill* 0x000000002ffce000 0x5000
0x000000002ffd3000 __BL2_IMAGE_START__ = . -> BL2 Load address
*(.bl2_image*)
.bl2_image 0x000000002ffd3000 0x1166c build/stm32mp1/stm32mp1.o
0x000000002ffe466c __BL2_IMAGE_END__ = .
0x0000000000024b00 . = 0x24b00
*fill* 0x000000002ffe466c 0x2994
0x000000002ffe7000 __BL32_IMAGE_START__ = . -> BL32 Load address
*(.bl32_image*)
.bl32_image 0x000000002ffe7000 0x1744c build/stm32mp1/stm32mp1.o
0x000000002fffe44c __BL32_IMAGE_END__ = .
0x000000002fffe44c __DATA_END__ = .
0x000000002fffe44c __TF_END__ = .
...
In this example:
- BL2 load address is 0x2ffd3000.
- BL32 load address is 0x2ffe7000.
You can load all your symbols directly:
(gdb) add-symbol-file <path_to_build_folder>/tf-a-bl2.elf 0x2ffd3000 (gdb) add-symbol-file <path_to_build_folder>/tf-a-bl32.elf 0x2ffe7000
Set your hardware breakpoint and reset:
(gdb) hb bl2_early_platform_setup (gdb) monitor reset halt
2.3.2. Debugging during runtime execution[edit source]
Once U-Boot or the Linux kernel is running, you cannot access secure memory or regions, but you can break, set a hardware breakpoint into SMC handler (in BL32). GDB breaks once it has switched into the secure world and reached the break instruction. Once halted in the secure monitor, GDB can access secure resources as IPs or memory. For example, one can break into kernel:
(gdb) hb stm32mp1_svc_smc_handler (gdb) continue
On the first SMC call occurence GDB breaks the stm32mp1_svc_smc_handler() entry in BL32.