Stack Size Analysis Tool for EC Firmware

This tool does static analysis on EC firmwares to get the maximum stack usage of each function and task. The maximum stack usage of a function includes the stack used by itself and the functions it calls.

Usage

Make sure the firmware of your target board has been built.

In src/platform/ec, run

make BOARD=${BOARD} SECTION=${SECTION} ANNOTATION=${ANNOTATION} analyzestack

The ${SECTION} can be RO or RW. The ${ANNOTATION} is a optional annotation file, see the example_annotation.yaml, by default, board/$BOARD/analyzestack.yaml is used.

Output

For each task, it will output the result like below,

Task: PD_C1, Max size: 1156 (932 + 224), Allocated size: 640
Call Trace:
    pd_task (160) [common/usb_pd_protocol.c:1644] 1008a6e8
        -> pd_task[common/usb_pd_protocol.c:1808] 1008ac8a
           - handle_request[common/usb_pd_protocol.c:1191]
             - handle_data_request[common/usb_pd_protocol.c:798]
        -> pd_task[common/usb_pd_protocol.c:2672] 1008c222
        -> [annotation]
    pd_send_request_msg.lto_priv.263 (56) [common/usb_pd_protocol.c:653] 1009a0b4
        -> pd_send_request_msg.lto_priv.263[common/usb_pd_protocol.c:712] 1009a22e0

The pd_task uses 160 bytes on the stack and calls pd_send_request_msg.lto_priv.263.

The callsites to the next function will be shown like below,

-> pd_task[common/usb_pd_protocol.c:1808] 1008ac8a
   - handle_request[common/usb_pd_protocol.c:1191]
     - handle_data_request[common/usb_pd_protocol.c:798]
-> pd_task[common/usb_pd_protocol.c:2672] 1008c222
-> [annotation]

This means one callsite to the next function is at usb_pd_protocol.c:798, but it is inlined to the current function and you can follow the trace: usb_pd_protocol.c:1808 -> usb_pd_protocol.c:1191 -> usb_pd_protocol.c:798 to find the callsite. The second callsite is at usb_pd_protocol.c:2672. And the third one is added by annotation.

The unresolved indirect callsites have the similar format to the above.

Annotating Indirect Call

To annotate an indirect call like this,

Unresolved indirect callsites:
    pd_transmit
        -> pd_transmit[common/usb_pd_protocol.c:407] 802c9c8
           - tcpm_transmit[driver/tcpm/tcpm.h:142]

It is an indirect call in the tcpm_transmit, which is inlined to the pd_transmit.

You can add a annotation like the below to eliminate it.

add:
  tcpm_transmit[driver/tcpm/tcpm.h:142]:
  - anx74xx_tcpm_transmit

The source tcpm_transmit[driver/tcpm/tcpm.h:142] must be a full signature (function_name[path:line number]). So the resolver can know which indirect call you want to annotate and eliminate (even if it is inlined).

Annotating arrays (hooks, console commands, host commands)

When a callsite calls a number of functions based on values from an constant array (in .rodata section), one can use the following syntax:

  hook_task[common/hooks.c:197]:
    - { name: __deferred_funcs, stride: 4, offset: 0 }
    - { name: __hooks_second, stride: 8, offset: 0 }
    - { name: __hooks_tick, stride: 8, offset: 0 }

Where name is the symbol name for the start of the array (the end of the array is <name>_end), stride is the array element size, and offset is the offset of the function pointer in the structure. For example, above, __deferred_funcs is a simple array of function pointers, while __hooks_tick is an array of struct hook_data (size 8, pointer at offset 0):

struct hook_data {
        /* Hook processing routine. */
        void (*routine)(void);
        /* Priority; low numbers = higher priority. */
        int priority;
};