Suggesting removal of dependency on libc on Linux systems

[renehsz]

As libc is a bloated, large, old and non-required library for creating programs, I think we should not depend on it in the standard library (and core:os_linux.odin in particular).

All we need from libc is the bindings to the Unix syscalls, whilst we are still linking in all the other C stuff, which we don't need.

[gingerBill]

This will be a goal in the future but it is not a huge priority at the moment.

[rdebath]

It struck me that it may be sufficient to link using -static, but if I do that directly I get quite a bit of other material from libc (looks like the horrible pre-main dependencies). So the second I tried was to use "diet" libc, unfortunately, this doesn't have the syscall external, however, it does have the gettid function.

This creates an executable that is SMALLER than the shared library version!

Note: You don't always use the -lm library so for the shared version I replaced "-lm" by "-Wl,--as-needed -lm -Wl,--no-as-needed".

Now I'm stuck. I've attached the minor changes I made to the end of this message. I think the "best" short term next step might be to copy&paste the relevant functions from dietlibc and include them as a tiny *.a file to replace gnulibc. But supporting diet now might be the most reasonable assuming those functions will be translated to Odin in a little while. There is also the question of how assembler functions or inclusions might be handled.

odin-lang$ rm x
odin-lang$ sc ./odin build x.odin
odin-lang$ ls -l x
-rwxr-xr-x 1 robert robert 194480 Jan  2 12:43 x
odin-lang$ size x
   text    data     bss     dec     hex filename
 166762   14480   14476  195718   2fc86 x
odin-lang$ ldd x
        not a dynamic executable
odin-lang$

odin-lang$ rm x
odin-lang$ sc ./odin build x.odin
odin-lang$ l x
-rwxr-xr-x 1 robert 198984 Jan  2 12:43 x
odin-lang$ size x
   text    data     bss     dec     hex filename
 167244   15061   14320  196625   30011 x
odin-lang$ ldd x
        linux-vdso.so.1 (0x00007fff1dfc5000)
        libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007fd3aeea3000)
        /lib64/ld-linux-x86-64.so.2 (0x00007fd3af242000)
odin-lang$

diff --git a/core/os/os_linux.odin b/core/os/os_linux.odin
index 6e60f0e..fa9511b 100644
--- a/core/os/os_linux.odin
+++ b/core/os/os_linux.odin
@@ -362,7 +362,9 @@ nanosleep :: proc(nanoseconds: i64) -> int {
 }

 current_thread_id :: proc "contextless" () -> int {
-       return syscall(SYS_GETTID);
+       return cast(int) _unix_gettid();
+       // return syscall(SYS_GETTID);
+       // return 0;
 }

 dlopen :: inline proc(filename: string, flags: int) -> rawptr {
diff --git a/src/main.cpp b/src/main.cpp
index a6838dd..7cfc20e 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -1059,7 +1059,7 @@ int main(int arg_count, char **arg_ptr) {
                        if (str_eq_ignore_case(cross_compile_target, str_lit("Essence"))) {
                                linker = "x86_64-elf-gcc -T core/sys/essence_linker_userland64.ld -ffreestanding -nostdlib -lgcc -g -z max-page-size=0x1000 -Wno-unused-command-line-argument";
                        } else {
-                               linker = "clang -Wno-unused-command-line-argument";
+                               linker = "diet clang -m64 -Wno-unused-command-line-argument";
                        }
                #endif

@@ -1079,7 +1079,7 @@ int main(int arg_count, char **arg_ptr) {
                        #endif
                        , linker, LIT(output_base), LIT(output_base), output_ext,
                        lib_str,
-                       str_eq_ignore_case(cross_compile_target, str_lit("Essence")) ? "-lfreetype -lglue" : "-lc -lm",
+                       str_eq_ignore_case(cross_compile_target, str_lit("Essence")) ? "-lfreetype -lglue" : "-lc -Wl,--as-needed -lm -Wl,--no-as-needed ",
                        LIT(build_context.link_flags),
                        link_settings,
                        LIT(cross_compile_lib_dir)