kernel/tools/include/nolibc/crt.h, branch linux-rolling-stable

tools/nolibc: add option to disable runtime

2025-10-29T15:29:16Z

In principle, it is possible to use nolibc for only some object files in a program. In that case, the startup code in _start and _start_c is not going to be used. Add the NOLIBC_NO_RUNTIME compile time option to disable it entirely and also remove anything that depends on it. Doing this avoids warnings from modpost for UML as the _start_c code references the main function from the .init.text section while it is not inside .init itself. Signed-off-by: Benjamin Berg Signed-off-by: Thomas Weißschuh

tools/nolibc: disable function sanitizer for _start_c()

2025-04-19T12:17:56Z

Both constructors and main() may be executed with different function signatures than they are actually using. This is intentional but trips up UBSAN. Disable the function sanitizer of UBSAN in _start_c(). Signed-off-by: Thomas Weißschuh Acked-by: Willy Tarreau Link: https://lore.kernel.org/r/20250419-nolibc-ubsan-v2-3-060b8a016917@weissschuh.net

tools/nolibc: add prototypes for non-static functions

2025-02-03T19:57:37Z

With -Wmissing-prototypes the compiler will warn about non-static functions which don't have a prototype defined. This warning doesn't make much sense for nolibc itself but for user code it is still useful. To pacify the compiler add prototypes next to the function definitions, similar to how it is handled elsewhere in the kernel. Acked-by: Willy Tarreau Link: https://lore.kernel.org/r/20250123-nolibc-prototype-v1-1-e1afc5c1999a@weissschuh.net Signed-off-by: Thomas Weißschuh

tools/nolibc: crt: mark _start_c() as used

2024-08-16T15:23:13Z

During LTO the reference from the asm startup code to the _start_c() function is not visible and _start_c() is removed. This will then lead to errors during linking. As _start_c() is indeed always used, mark it as such. Acked-by: Willy Tarreau Link: https://lore.kernel.org/r/20240812-nolibc-lto-v2-1-736af7bbefa8@weissschuh.net Signed-off-by: Thomas Weißschuh

tools/nolibc: pass argc, argv and envp to constructors

2024-08-09T05:40:18Z

Since 2005 glibc has passed argc, argv, and envp to all constructors. As it is cheap and easy to do so, mirror that behaviour in nolibc. This makes it easier to migrate applications to nolibc. Link: https://lore.kernel.org/r/20240728-nolibc-constructor-args-v1-1-36d0bf5cd4c0@weissschuh.net Signed-off-by: Thomas Weißschuh

tools/nolibc: add support for constructors and destructors

2023-10-12T19:14:16Z

With the startup code moved to C, implementing support for constructors and deconstructors is fairly easy to implement. Examples for code size impact: text data bss dec hex filename 21837 104 88 22029 560d nolibc-test.before 22135 120 88 22343 5747 nolibc-test.after 21970 104 88 22162 5692 nolibc-test.after-only-crt.h-changes The sections are defined by [0]. [0] https://refspecs.linuxfoundation.org/elf/gabi4+/ch5.dynamic.html Signed-off-by: Thomas Weißschuh Acked-by: Willy Tarreau Link: https://lore.kernel.org/lkml/20231007-nolibc-constructors-v2-1-ef84693efbc1@weissschuh.net/

tools/nolibc: mark start_c as weak

2023-10-12T19:13:51Z

Otherwise the different instances of _start_c from each compilation unit will lead to linker errors: /usr/bin/ld: /tmp/ccSNvRqs.o: in function `_start_c': nolibc-test-foo.c:(.text.nolibc_memset+0x9): multiple definition of `_start_c'; /tmp/ccG25101.o:nolibc-test.c:(.text+0x1ea3): first defined here Fixes: 17336755150b ("tools/nolibc: add new crt.h with _start_c") Signed-off-by: Thomas Weißschuh Link: https://lore.kernel.org/lkml/20231012-nolibc-start_c-multiple-v1-1-fbfc73e0283f@weissschuh.net/ Link: https://lore.kernel.org/lkml/20231012-nolibc-linkage-test-v1-1-315e682768b4@weissschuh.net/ Acked-by: Willy Tarreau

tools/nolibc: stackprotector.h: make __stack_chk_init static

2023-08-23T03:17:07Z

This allows to generate smaller text/data/dec size. As the _start_c() function added by crt.h, __stack_chk_init() is called from _start_c() instead of the assembly _start. So, it is able to mark it with static now. Reviewed-by: Thomas Weißschuh Signed-off-by: Zhangjin Wu Signed-off-by: Willy Tarreau

tools/nolibc: crt.h: initialize stack protector

2023-08-23T02:40:22Z

As suggested by Thomas, It is able to move the stackprotector initialization from the assembly _start to the beginning of the new _start_c(). Let's call __stack_chk_init() in _start_c() as a preparation. Suggested-by: Thomas Weißschuh Link: https://lore.kernel.org/lkml/a00284a6-54b1-498c-92aa-44997fa78403@t-8ch.de/ Signed-off-by: Zhangjin Wu Signed-off-by: Willy Tarreau

tools/nolibc: add new crt.h with _start_c

2023-08-23T02:40:22Z

As the environ and _auxv support added for nolibc, the assembly _start function becomes more and more complex and therefore makes the porting of nolibc to new architectures harder and harder. To simplify portability, this C version of _start_c() is added to do most of the assembly start operations in C, which reduces the complexity a lot and will eventually simplify the porting of nolibc to the new architectures. The new _start_c() only requires a stack pointer argument, it will find argc, argv, envp/environ and _auxv for us, and then call main(), finally, it exit() with main's return status. With this new _start_c(), the future new architectures only require to add very few assembly instructions. As suggested by Thomas, users may use a different signature of main (e.g. void main(void)), a _nolibc_main alias is added for main to silence the warning about potential conflicting types. As suggested by Willy, the code is carefully polished for both smaller size and better readability with local variables and the right types. Suggested-by: Willy Tarreau Link: https://lore.kernel.org/lkml/20230715095729.GC24086@1wt.eu/ Suggested-by: Thomas Weißschuh Link: https://lore.kernel.org/lkml/90fdd255-32f4-4caf-90ff-06456b53dac3@t-8ch.de/ Signed-off-by: Zhangjin Wu Signed-off-by: Willy Tarreau