GNU MCU Eclipse RISC-V Embedded GCC v7.1.1-2-20170912-* released

Posted on September 13, 2017 by Liviu Ionescu.

Version v7.1.1-2-20170912-2255 is a new release of GNU MCU Eclipse RISC-V Embedded GCC; after the initial version of the riscv64-unknown-elf toolchain was released, it was discovered that it was intended more to applications that include a kernel-like environment, and less to bare-metal environments. This second release is intended to provide a temporary fix to this problem and make the toolchain more suitable for embedded bare-metal applications; for this it was necessary to to update to the latest newlib 2.5 release which uses ‘underscore’ syscall functions and to remove the mandatory use of libgloss. Hopefully the official toolchain distribution will follow shortly and use the same approach.

In addition, based on users request, support for a new march=rv32imaf/mabi=ilp32f library was added.

Binary files »

Compliance

All GNU MCU Eclipse RISC-V Embedded GCC releases are based on the official RISC-V source files maintained by SiFive.

The current version is based on the following commits:

• the riscv/riscv-gcc project, branch riscv-gcc-7, commit c95cdca from from Sep 12th, 2017, with a patch to remove the mandatory libgloss, as commit c95cdca
• the riscv/riscv-binutils-gdb project, branch riscv-binutils-2.29, commit 60cda8d from Sep 7th, 2017
• the riscv/riscv-newlib project, branch riscv-newlib-2.5.0, commit bcf3078 from Jul 12th, 2017

The supported architectures (-march=) are:

• rv32i[m][a][f[d]][c]
• rv32g[c]
• rv64i[m][a][f[d]][c]
• rv64g[c]

The supported ABIs (-mabi=) are:

• ilp32 (32-bit, soft-float)
• ilp32f (32-bit with single-precision in registers and double in memory, niche use only)
• ilp32d (32-bit, hard-float)
• lp64 (64-bit long and pointers, soft-float)
• lp64f (64-bit long and pointers, with single-precision in registers and double in memory, niche use only)
• lp64d (64-bit long and pointers, hard-float).

The supported libraries are (in parenthesis are combinations that reuse simpler libraries):

march=rv32i/mabi=ilp32 (march.rv32ic/mabi.ilp32)
march=rv32im/mabi=ilp32 (march.rv32imc/mabi.ilp32)
march=rv32iac/mabi=ilp32
march=rv32imac/mabi=ilp32
march=rv32imaf/mabi=ilp32f <-- New
march=rv32imafc/mabi=ilp32f (march.rv32imafdc/mabi.ilp32f, march.rv32gc/mabi.ilp32f)
march=rv64imac/mabi=lp64
march=rv64imafdc/mabi=lp64d (march.rv64gc/mabi.lp64d)

Please note that, although all combinations of march/mabi are supported by the compiler, not all of them have libraries.

Improvements

Compared to the original RISC-V riscv64-unknown-elf toolchain, the following improvements can be noted:

• a newer newlib was included, which supports the ‘underscore’ syscall functions
• the mandatory reference to libgloss in the linker configuration was removed
• the march=rv32imaf/mabi=ilp32f library was added to the list of multilibs
• support for newlib-nano was added
• the standard documentation, in PDF and HTML, was added

newlib-nano

Currently GNU MCU Eclipse RISC-V Embedded GCC is the only RISC-V toolchain that provides support for newlib-nano, using the --specs=nano.specs option.

If no syscalls are needed, --specs=nosys.specs can be used at link time to provide empty implementations for the POSIX system calls.

The nano versions of the libraries are configured with simplified implementations for printf() and malloc(); in addition they are compiled with -Os, while the regular versions are compiled with -O2.

‘Underscore’ newlib syscalls

The initial RISC-V newlib was erroneously configured to directly call system functions via their direct names (like write()), assuming they are implemented via kernel traps in libgloss.

The latest newlib 2.5.0 for RISC-V fixed this, and switched to the usual newlib configuration, which uses ‘underscore’ functions (like _write()) that must be defined by the application to implement the system calls.

This change is welcome, since it brings the RISC-V toolchain in line with other toolchains, like arm-none-eabi.

Unfortunately this change breaks the builds for the initial SiFive SDK samples, which implements the direct function names in the libwrap library. To fix them, libwrap should no longer be used, the --wrap options should no longer be passed to the linker, and several functions (like _write(), _istty(), …) must be implemented by the application.

libgloss

For RISC-V, this library implements all syscalls via kernel traps; on other platforms (like ARM) it is used for semihosting.

The GNU MCU Eclipse RISC-V Embedded GCC toolchain no longer links automatically libgloss; however libgloss is still available in the distribution and applications that need to access a kernel can include it using the usual -lgloss link option.

Documentation

Another addition compared to the official distribution is the presence of the documentation files, including the PDF manuals for all tools.

Binaries

Binaries for Windows, macOS and GNU/Linux are provided. For Windows and macOS, separate installable and plain archives are provided. For Windows and GNU/Linux, both 32/64-bit binaries are provided.

Instructions on how to install them are available in the How to install the RISC-V toolchain? page.

For better control and repeatability, the build scripts use Docker containers; all files required during builds are available as a separate gnu-mcu-eclipse/riscv-none-gcc-build project.

Checksums

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