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chromium/external/github.com/emscripten-core/emscripten/b1fee4acdc102bcf127776d222547560f026fa45/./system/lib/libc
tree: 7b516aadb45e4bc19627c97d3bda263ca1efa62b
  1. compat/
  2. musl/
  3. atexit_dummy.c
  4. crt1.c
  5. crt1_proxy_main.c
  6. crt1_reactor.c
  7. dynlink.c
  8. emscripten_console.c
  9. emscripten_fiber.c
  10. emscripten_get_heap_size.c
  11. emscripten_internal.h
  12. emscripten_libc_stubs.c
  13. emscripten_memcpy.c
  14. emscripten_memcpy_bulkmem.S
  15. emscripten_memmove.c
  16. emscripten_memset.c
  17. emscripten_memset_bulkmem.S
  18. emscripten_mmap.c
  19. emscripten_scan_stack.c
  20. emscripten_syscall_stubs.c
  21. emscripten_time.c
  22. emscripten_yield_stub.c
  23. kill.c
  24. lookup_name.c
  25. mktime.c
  26. pthread_sigmask.c
  27. raise.c
  28. README.md
  29. sbrk.c
  30. sigaction.c
  31. sigtimedwait.c
  32. system.c
  33. update_alltypes.sh
  34. wasi-helpers.c
system/lib/libc/README.md

This folder contains the musl version of libc at /musl. The upstream version can be found at http://www.musl-libc.org/.

Most of the source comes from musl v1.2.5, with some exceptions listed below. We track these changes from upstream in https://github.com/emscripten-core/musl and use a script (system/lib/update_musl.py) to pull in updates.

Some changes have been made to the version that was taken from upstream, including:

  • Emscripten-specific changes (from before this readme existed). These should be marked with XXX EMSCRIPTEN in the source, or ifdefed with #if __EMSCRIPTEN__. They are mostly in pthreads code and hopefully temporary.
  • Backporting an operator-precedence warning fix from 6e76e1540fc58a418494bf5eb832b556f9c5763e in the upstream version.
  • Switch to using the wasi fd_write syscall instead of writev.
  • Simplify stdout stream handling: do not support seeking, terminal handling, etc., as it just increases code size and Emscripten doesn't have those features anyhow.
  • Setting _POSIX_REALTIME_SIGNALS and _POSIX_SPAWN macros to -1, to exclude unsupported functions.
  • Handling trailing % in strftime and wcsftime format strings.

Copy log.c and log2.c from earlier version of musl which result in smaller binary size since they do not rely on data tables in log_data.c and log2_data.c. See https://github.com/emscripten-core/emscripten/issues/15483.

Verifying upstream musl behaviour

Occasionally when working on libc/musl it can be useful to verify to behavior of upstream musl. For example, when trying to determine if a certain behavior is a bug in emscripten, or an upstream bug, or just expected musl behavior.

When I need to do this I use the Alpine linux docker image. Alpine linux is a distro where the sysmtem libc is musl so by default any program you build within the contains will be using musl libc.

$ docker run --rm -it -v "$(pwd):/data" alpine /bin/sh

Then from inside the new container you can run tests against Alpine's musl libc. For example:

$ apk add build-base
$ cd /data
$ gcc -pthread test/pthread/test_pthread_cancel_async.c
$ ./a.out