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There is a problem with the current elf loader for risc-v: when a pair of PCREL_HI20 / LO12 relocations are encountered, it is assumed that these will follow each other immediately, as follows: label: auipc a0, %pcrel_hi(symbol) // R_RISCV_PCREL_HI20 load/store a0, %pcrel_lo(label)(a0) // R_RISCV_PCREL_LO12_I/S With this assumption, the hi/lo relocations are both done when a hi20 relocation entry is encountered, first to the current instruction (addr) and to the next instruction (addr + 4). However, this assumption is wrong. There is nothing in the elf relocation specification[1] that mandates this. Thus, the hi/lo relocation always needs to first fixup the hi-part, and when the lo-part is encountered, it needs to find the corresponding hi relocation entry, via the given "label". This necessitates (re-)visiting the relocation entries for the current section as well as looking for "label" in the symbol table. The NuttX elf loader does not allow such operations to be done in the machine specific part, so this patch fixes the relocation issue by introducing an architecture specific cache for the hi20 relocation and symbol table entries. When a lo12 relocation is encountered, the cache can be consulted to find the hi20 part. [1] https://github.com/riscv-non-isa/riscv-elf-psabi-doc/blob/master/riscv-elf.adoc
Apache NuttX is a real-time operating system (RTOS) with an emphasis on standards compliance and small footprint. Scalable from 8-bit to 64-bit microcontroller environments, the primary governing standards in NuttX are POSIX and ANSI standards. Additional standard APIs from Unix and other common RTOSs (such as VxWorks) are adopted for functionality not available under these standards, or for functionality that is not appropriate for deeply-embedded environments (such as fork()).
For brevity, many parts of the documentation will refer to Apache NuttX as simply NuttX.
Getting Started
First time on NuttX? Read the Getting Started guide! If you don't have a board available, NuttX has its own simulator that you can run on terminal.
Documentation
You can find the current NuttX documentation on the Documentation Page.
Alternatively, you can build the documentation yourself by following the Documentation Build Instructions.
The old NuttX documentation is still available in the Apache wiki.
Supported Boards
NuttX supports a wide variety of platforms. See the full list on the Supported Platforms page.
Contributing
If you wish to contribute to the NuttX project, read the Contributing guidelines for information on Git usage, coding standard, workflow and the NuttX principles.
License
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