# Picolibc for Hexagon: User Guide

**Document:** 80-N2040-103

This guide is for application developers who want to compile programs against
picolibc using the Hexagon toolchain. It covers compilation flags, linker
scripts, runtime environments, and worked examples.

## Documents

| Document | What it covers |
| --- | --- |
| [Getting Started](https://docs.qualcomm.com/doc/80-N3040-23/topic/getting-started.html) | Minimal compile + run from zero — prerequisites, hello world, toolchain verification |
| [H2 + Picolibc](https://docs.qualcomm.com/doc/80-N3040-23/topic/picolibc-h2.html) | Compiling for the H2 hypervisor target, heap/stack config, TLS, memory layout |
| [Bare-Metal + Picolibc](https://docs.qualcomm.com/doc/80-N3040-23/topic/picolibc-baremetal.html) | Compiling for bare-metal Hexagon targets (no OS, QEMU semihosting) |
| [Semihosting](https://docs.qualcomm.com/doc/80-N3040-23/topic/semihosting.html) | TRAP0 interface, syscall opcodes, file I/O, QEMU integration |

## Which guide do I need?

Are you running under H2 hypervisor?
      Yes  → picolibc-h2.md
      No   →
        Is there a host debugger/QEMU to talk to?
          Yes  → picolibc-baremetal.md  (semihosting section)
          No   → picolibc-baremetal.md  (no-semihosting / stub I/O section)
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## Key flags at a glance

All picolibc compilations share two mandatory flags:

--target=hexagon-unknown-<os>-elf   # selects the target ABI and sysroot
    --cstdlib=picolibc                  # selects picolibc instead of the default libc
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The `<os>` field distinguishes the runtime environment:

| `<os>` value | Runtime | Use when |
| --- | --- | --- |
| `h2` | H2 hypervisor | Running on H2 (simulator or hardware with H2) |
| `none` | bare-metal | No OS; semihosting via QEMU or stub I/O |

Last Published: Oct 06, 2026

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