Provide support for Picolibc #26545

keith-packard · 2020-06-30T19:36:52Z

Picolibc is a libc implementation designed for and tested on small embedded systems.

Features:

Smaller stdio implementation (originally from avr-libc)
Malloc-free printf/scanf
"Exact" float/string conversions based on the Ryu method.
ABI-compatible thread-local storage (use __thread in applications)
Tested under QEMU on a range of RISC-V and ARM targets.

Porting to additional architectures requires initializing the per-CPU thread pointer in the context
switch code. On ARM, this requires a toolchain with TLS support (GCC in Debian is built correctly).

A sample program linked for cortex-m0 shows the following memory usage:

void main(void)
{
    	printf("Hello World! %s %d\n", CONFIG_BOARD, 12);
}

text	data	bss	dec	hex	version
16908	428	4917	22253	56ed	minimal
15460	464	4924	20848	5170	picolibc integer-only
20272	464	4924	25660	643c	picolibc full version
20862	548	4936	26346	66ea	newlib-nano integer-only
50542	916	4936	56394	dc4a	newlib-nano full version
48170	2924	4984	56078	db0e	newlib

mbolivar-nordic

Looks cool. I have a couple of drive-by build system questions.

mbolivar-nordic · 2020-06-30T22:16:01Z

cmake/toolchain/gnuriscvemb/generic.cmake

Since GNURISCVEMB_TOOLCHAIN_PATH is new, why bother adding environment variable support for setting its value in an already deprecated state? A plain CMake variable should do, no?

I'll see if I can figure this out; I just followed the existing gnuarmemb path for this work.

More a question than a request for change, since I recall some historical back and forth around what configuration variables fall back to the environment if not set as ordinary CMake variables. I defer to @tejlmand as build system maintainer for what the right thing to do is here.

boards/riscv/qemu_riscv32/qemu_riscv32.yaml

stephanosio · 2020-07-01T05:25:48Z

Welcome to Zephyr! Glad to see that a regular newlib contributor is helping out with the project :)

cmake/extensions.cmake

stephanosio · 2020-07-01T05:44:22Z

@galak I suppose we could potentially integrate this into the Zephyr SDK/toolchains by adding pico.specs.

@keith-packard Do you have any plans to add something like pico.specs for GCC integration so that various C libraries can be selected (e.g. libc.a for full newlib and libc_pico.a for picolibc)? Also any plans to support crosstool-ng? The Zephyr toolchains are currently built using crosstool-ng.

keith-packard · 2020-07-01T06:03:38Z

@galak I suppose we could potentially integrate this into the Zephyr SDK/toolchains by adding pico.specs.

I think you should be able to use the existing picolibc.specs file if you wanted to deliver picolibc as part of the Zephyr SDK/toolchains. The picolibc configuration supports sysroot-based GCC installs, which I suspect is what the SDK is using. That means you would be able to place picolibc relative to GCC install directory and picolibc.specs would then be able to locate picolibc wherever the SDK was installed.

@keith-packard Do you have any plans to add something like pico.specs for GCC integration so that various C libraries can be selected (e.g. libc.a for full newlib and libc_pico.a for picolibc)? Also any plans to support crosstool-ng? The Zephyr toolchains are currently built using crosstool-ng.

The PR already depends on the picolibc.specs file which is shipped and installed with picolibc itself, so there's no need to include an additional specs file in zephyr.

If there are additional zephyr-specific compiler configuration bits needed, we could create a separate .specs file that referenced the existing picolibc one. The advantage of using the installed picolibc.specs file is that it has the picolibc install paths configured so that you don't need any library or include paths for the toolchain.

keith-packard · 2020-07-01T06:04:19Z

Welcome to Zephyr! Glad to see that a regular newlib contributor is helping out with the project :)

Been meaning to drop by for a while now. Thanks for the warm welcome.

arch/arm/core/aarch64/switch.S

keith-packard · 2020-10-27T02:00:38Z

I've updated this patch to sit on top of current master and require THREAD_LOCAL_STORAGE for architectures which support that. The changes are now far smaller as they don't include the TLS code.

Neither of these libraries can support the built-in Zephyr errno code, so make sure it gets disabled when either are selected Signed-off-by: Keith Packard <[email protected]>

Picolibc is a fork of newlib designed and tested on embedded systems. It offers a smaller memory footprint (both ROM and RAM), and native TLS support, which uses the Zephyr TLS support. By default, the full printf version is included in the executable, which includes exact floating point and long long input and output. A configuration option has been added to switch to the integer-only version (which also omits long long support). Here are some size comparisons using qemu-cortex-m0 and this application (parameters passed to printf to avoid GCC optimizing it into puts): void main(void) { printf("Hello World! %s %d\n", CONFIG_BOARD, 12); } text data bss dec hex 16908 428 4917 22253 56ed minimal 15460 464 4924 20848 5170 picolibc integer-only 20272 464 4924 25660 643c picolibc full version 20862 548 4936 26346 66ea newlib-nano integer-only 50542 916 4936 56394 dc4a newlib-nano full version 48170 2924 4984 56078 db0e newlib Signed-off-by: Keith Packard <[email protected]> --- v2: Include picolibc-tls.ld v3: Document usage in guides/c_library.rst and getting_started/toolchain_other_x_compilers.rst v4: Lost the lib/libc/picolibc directory somehow! v5: Add PICOLIBC_ALIGNED_HEAP_SIZE configuration option. Delete PICOLIBC_SEMIHOST option support code v6: Don't allocate static RAM for TLS values; TLS values only need to be allocated for each thread. v7: Use arm coprocessor for TLS pointer storage where supported for compatibility with the -mtp=cp15 compiler option (or when the target cpu type selects this option) Add a bunch of tests Round TLS segment up to stack alignment so that overall stack remains correctly aligned Add aarch64 support Rebase to upstream head v8: Share NEWLIB, NEWLIB_NANO and PICOLIBC library configuration variables in a single LIBC_PARTITIONS variable instead of having separate PICOLIBC_PART and NEWLIB_PART variables. v9: Update docs to reference pending sdk-ng support for picolibc v10: Support memory protection by creating a partition for picolibc shared data and any pre-defined picolibc heap. v11: Fix formatting in arch/arm/core/aarch64/switch.S v12: Remove TLS support from this patch now that TLS is upstream Require THREAD_LOCAL_STORAGE when using PICOLIBC for architectures that support it. Signed-off-by: Keith Packard <[email protected]>

tejlmand

Thanks for the updated work.
Looks good, only a couple of small suggestions.

tejlmand · 2020-11-05T12:40:27Z

CMakeLists.txt

+  if(CONFIG_PICOLIBC)
+    set(LIBC_PARTITIONS -l libc.a z_libc_partition)
+  endif()
  if(CONFIG_NEWLIB_LIBC)
-    set(NEWLIB_PART -l libc.a z_libc_partition)
+    set(LIBC_PARTITIONS -l libc.a z_libc_partition)


How about:

if(CONFIG_PICOLIBC OR CONFIG_NEWLIB_LIBC) set(LIBC_PARTITIONS -l libc.a z_libc_partition) endif()

tejlmand · 2020-11-05T12:44:06Z

lib/libc/CMakeLists.txt

+if(CONFIG_PICOLIBC)
+  add_subdirectory(picolibc)
+else()
 if(CONFIG_NEWLIB_LIBC)
  add_subdirectory(newlib)
 else()
  add_subdirectory(minimal)
 endif()
+endif()


Please make an elseif() in this case.

Suggested change

if(CONFIG_PICOLIBC)

add_subdirectory(picolibc)

else()

if(CONFIG_NEWLIB_LIBC)

add_subdirectory(newlib)

else()

add_subdirectory(minimal)

endif()

endif()

if(CONFIG_PICOLIBC)

add_subdirectory(picolibc)

elseif(CONFIG_NEWLIB_LIBC)

add_subdirectory(newlib)

else()

add_subdirectory(minimal)

endif()

tejlmand · 2020-11-05T12:49:39Z

lib/libc/picolibc/libc-hooks.c

+}
+
+static int
+z_putc(char c, FILE *file)


why a newline here ?

tejlmand · 2020-11-05T12:51:52Z

lib/libc/picolibc/libc-hooks.c

+}
+
+static int
+z_getc(FILE *file)


why a newline here ?

tejlmand · 2020-11-05T12:58:06Z

lib/libc/picolibc/CMakeLists.txt

+zephyr_link_libraries(
+  m
+  c
+  gcc # Lib C depends on libgcc.


No changes requested, but with the fact that Zephyr is working towards more toolchains, especially LLVM, and thus also the support of compiler-rt runtime library, I was wondering if picolib could be used in that case.

Also this makes me wonder if the use of picolib should be restricted, based on toolchain in use.
But that would probably need to go into a bigger work at later time.

picolibc built with llvm still requires libgcc as that has all of the helper functions required by the underlying ABI, such as the __aeabi functions for ARM. -lgcc would be automatically inserted into the link command by the compiler front-end (either clang or gcc) if zephyr wasn't using -nostdlib. zephyr could probably remove that flag and simply let the compiler front end insert both -lc and -lgcc.

github-actions · 2021-01-05T01:45:12Z

This pull request has been marked as stale because it has been open (more than) 60 days with no activity. Remove the stale label or add a comment saying that you would like to have the label removed otherwise this pull request will automatically be closed in 14 days. Note, that you can always re-open a closed pull request at any time.

keith-packard requested review from MaureenHelm, andrewboie, andyross, carlescufi, galak, ioannisg, kgugala, nashif, nategraff-sifive, pgielda and tejlmand as code owners June 30, 2020 19:36

github-actions bot added area: API Changes to public APIs area: ARM ARM (32-bit) Architecture area: Boards area: Build System area: Kernel area: RISCv32/64 labels Jun 30, 2020

keith-packard force-pushed the picolibc branch from 40094bd to e7135c3 Compare June 30, 2020 19:58

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andrewboie mentioned this pull request Aug 27, 2020

Add Thread Local Storage (TLS) support #22185

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tejlmand mentioned this pull request Sep 18, 2020

riscv: Fix passing -mabi/-march to linker #28464

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per-memory domain copies of libc globals #25891

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keith-packard added 2 commits October 26, 2020 19:46

libc: disable CONFIG_ERRNO when using newlib or newlib-nano

1cb6463

Neither of these libraries can support the built-in Zephyr errno code, so make sure it gets disabled when either are selected Signed-off-by: Keith Packard <[email protected]>

keith-packard force-pushed the picolibc branch from 90ef364 to 5413f80 Compare October 27, 2020 02:50

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yashi mentioned this pull request May 12, 2021

libc/minimal: Add rand and srand #32667

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katsuster added area: RISCV RISCV Architecture (32-bit & 64-bit) and removed area: RISCv32/64 labels Jun 10, 2021

yashi mentioned this pull request Oct 7, 2021

test: ungetc fails with -Dposix-console=false picolibc/picolibc#179

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tejlmand mentioned this pull request Oct 20, 2021

lib/libc: Add picolibc support (aarch32, aarch64 and RISC-V) [v14] #39563

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stephanosio mentioned this pull request Mar 21, 2022

Add CMake support (Zephyr Module) picolibc/picolibc#177

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stephanosio mentioned this pull request Mar 30, 2022

Adding picolibc as a module #44143

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stephanosio mentioned this pull request Sep 5, 2022

Make picolibc the default C library for Zephyr #49922

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fanghuaqi mentioned this pull request Nov 21, 2022

Picolibc support riscv-collab/riscv-gnu-toolchain#1119

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Provide support for Picolibc #26545

Provide support for Picolibc #26545

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