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feat: hosted libstdc++ for x86_64-montauk - full C++ on MontaukOS

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The cross toolchain now builds real hosted C++: std::string, vector,
unique_ptr, iostreams and exceptions all work in a plain
x86_64-montauk-g++ invocation with no special flags. This is the
library that native cc1plus will link against for the GCC self-host.

crt1 now runs .preinit_array/.init_array before main and hooks
.fini_array through atexit (main returns via exit(), so destructors
run on both exit paths). Global constructors and libgcc's eh_frame
registration both ride this. GCC is reconfigured with
--enable-initfini-array (modern arrays instead of .ctors),
--with-newlib (satisfies libstdc++'s crossconfig for unknown hosts),
--disable-wchar_t and --disable-libstdcxx-pch; the montauk gcc patch
grows a hunk keeping os/generic ctype under --with-newlib (the
Montauk libc is not newlib).

libc additions harvested by the libstdc++ build: mbtowc/wctomb,
strxfrm, strtok/strtok_r, a real vfscanf/fscanf/scanf (character-
driven with widths and l/ll; also unblocks gprof later), fgetpos/
fsetpos/setbuf/fpos_t, modf plus the C99 float math variants
(acosf..tanhf, hypot/hypotf as wrappers), FP_* classification macros,
the full POSIX errno vocabulary, complete DT_* dirent types, and
mbstate_t.

The SDK ships the real libstdc++.a (was an empty stand-in), the C++
headers at 0:/sdk/include/c++, and cxx-test.elf (global ctor, string,
vector+sort, unique_ptr, throw/catch; exits 0 on 5/5). Ramdisk sits
at 1571 files, within the 2048 table.

Co-Authored-By: Claude Fable 5 <[email protected]>
This commit is contained in:
daniel
2026-07-16 23:06:50 +02:00
co-authored by Claude Fable 5
parent eadc79708f
commit 03d1a1bc2f
19 changed files with 480 additions and 8 deletions
Download Patch File Download Diff File Expand all files Collapse all files
programs/lib/libc/crt/crt1.c
+40 -1
View File
@@ -36,6 +36,38 @@ static inline long _sys2(long nr, long a1, long a2) {
extern int main(int argc, char** argv);
/* Global constructor/destructor tables. The linker provides these
boundary symbols whenever .preinit_array/.init_array/.fini_array
sections exist; the weak references make them all optional so plain
C programs keep working unchanged. Frame registration for C++
exceptions (crtbegin's frame_dummy) also arrives via .init_array. */
extern void (*__preinit_array_start[])(void) __attribute__((weak));
extern void (*__preinit_array_end[])(void) __attribute__((weak));
extern void (*__init_array_start[])(void) __attribute__((weak));
extern void (*__init_array_end[])(void) __attribute__((weak));
extern void (*__fini_array_start[])(void) __attribute__((weak));
extern void (*__fini_array_end[])(void) __attribute__((weak));
extern int atexit(void (*fn)(void));
extern void exit(int status);
static void _run_init_arrays(void) {
for (void (**f)(void) = __preinit_array_start; f < __preinit_array_end; f++) {
(*f)();
}
for (void (**f)(void) = __init_array_start; f < __init_array_end; f++) {
(*f)();
}
}
/* Destructors run in reverse registration order, hooked through
atexit so they also run when the program calls exit() directly. */
static void _run_fini_array(void) {
for (void (**f)(void) = __fini_array_end; f > __fini_array_start; f--) {
(*(f - 1))();
}
}
void _start(void) {
/* Static: 4 KiB args + 256 argv slots would crowd a 32 KiB stack. */
static char argbuf[4096];
@@ -77,6 +109,13 @@ void _start(void) {
argv[argc] = 0;
_sys1(SYS_EXIT, (long)main(argc, argv));
if (__fini_array_start != __fini_array_end) {
atexit(_run_fini_array);
}
_run_init_arrays();
/* exit() (not raw SYS_EXIT) so the atexit chain - including the
fini-array walker registered above - runs on return from main. */
exit(main(argc, argv));
__builtin_unreachable();
}