zephyrproject-rtos/zephyr

syscall stack usage report

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#27,189 opened on Jul 27, 2020

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EnhancementGood first issuearea: Memory Managementarea: Memory Protection

Description

Is your enhancement proposal related to a problem? Please describe. Syscalls run on fixed-sized privilege elevation stacks. There is a hard limit on how much stack space a system call can use because of this. We don't have good data on how much stack syscalls actually use.

Describe the solution you'd like I'd like to be able to use CONFIG_STACK_USAGE to be able to generate a report, for every API exposed with __syscall, the upper bound on stack usage. Outliers that exceed the default privilege stack size should be flagged as issues.

This usage data must be from the syscall perspective; the measurements have to start from the syscall trap handler, through the verification and marshalling functions. We could probably get by with starting measurements at each mrsh function for every syscall; trap handler overhead would be a constant value added to the result.

Contributor guide

Tech stack
c
Domain
performancetooling
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
4
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
over 1 week
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
C programmingZephyr RTOS internalssyscall architecture
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
20
Research direction
Investigate the existing CONFIG STACK USAGE infrastructure and its integration with the syscall path. Focus on adding instrumentation at each 'mrsh' function to measure stack usage from the syscall trap handler through verification and marshalling. Identify the relevant files such as kernel/syscall.c, include/syscall handler.h, and architecture specific trap handlers. Consider using a mechanism to report upper bound per syscall and flag outliers exceeding the default privilege stack size.