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tools/nolibc: also mention how to build by just setting the include path

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Now that a few basic include files are provided, some simple portable
programs may build, which will save them from having to surround their
includes with #ifndef NOLIBC. This patch mentions how to proceed, and
enumerates the list of files that are covered.

A comprehensive list of required include files is available here:

  https://en.cppreference.com/w/c/header

Signed-off-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Willy Tarreau 2022-02-07 17:23:53 +01:00 committed by Paul E. McKenney
parent cec1505321
commit c4486e9728
1 changed files with 20 additions and 10 deletions
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30
tools/include/nolibc/nolibc.h
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@ -57,22 +57,32 @@
* having to specify anything.
*
* Finally some very common libc-level functions are provided. It is the case
* for a few functions usually found in string.h, ctype.h, or stdlib.h. Nothing
* is currently provided regarding stdio emulation.
* for a few functions usually found in string.h, ctype.h, or stdlib.h.
*
* The macro NOLIBC is always defined, so that it is possible for a program to
* check this macro to know if it is being built against and decide to disable
* some features or simply not to include some standard libc files.
*
* Ideally this file should be split in multiple files for easier long term
* maintenance, but provided as a single file as it is now, it's quite
* convenient to use. Maybe some variations involving a set of includes at the
* top could work.
* The nolibc.h file is only a convenient entry point which includes all other
* files. It also defines the NOLIBC macro, so that it is possible for a
* program to check this macro to know if it is being built against and decide
* to disable some features or simply not to include some standard libc files.
*
* A simple static executable may be built this way :
* $ gcc -fno-asynchronous-unwind-tables -fno-ident -s -Os -nostdlib \
* -static -include nolibc.h -o hello hello.c -lgcc
*
* Simple programs meant to be reasonably portable to various libc and using
* only a few common includes, may also be built by simply making the include
* path point to the nolibc directory:
* $ gcc -fno-asynchronous-unwind-tables -fno-ident -s -Os -nostdlib \
* -I../nolibc -o hello hello.c -lgcc
*
* The available standard (but limited) include files are:
* ctype.h, errno.h, signal.h, stdio.h, stdlib.h, string.h, time.h
*
* In addition, the following ones are expected to be provided by the compiler:
* float.h, stdarg.h, stddef.h
*
* The following ones which are part to the C standard are not provided:
* assert.h, locale.h, math.h, setjmp.h, limits.h
*
* A very useful calling convention table may be found here :
* http://man7.org/linux/man-pages/man2/syscall.2.html
*