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First stab at having the GC scan the shadow stack. #5

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Merged
ltratt merged 1 commit into from
Mar 13, 2026
Merged

First stab at having the GC scan the shadow stack. #5

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8 changes: 8 additions & 0 deletions ports/unix/main.c
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Original file line number Diff line number Diff line change
Expand Up @@ -57,6 +57,10 @@
#include "stack_size.h"
#include "shared/runtime/pyexec.h"

#ifdef USE_YK
#include <yk.h>
#endif

// Command line options, with their defaults
bool mp_compile_only = false;
static uint emit_opt = MP_EMIT_OPT_NONE;
Expand Down Expand Up @@ -443,6 +447,10 @@ int main(int argc, char **argv) {
// Define a reasonable stack limit to detect stack overflow.
mp_uint_t stack_size = 40000 * UNIX_STACK_MULTIPLIER;

#ifdef USE_YK
yk_init();
#endif

// We should capture stack top ASAP after start, and it should be
// captured guaranteedly before any other stack variables are allocated.
// For this, actual main (renamed main_) should not be inlined into
Expand Down
16 changes: 16 additions & 0 deletions shared/runtime/gchelper_generic.c
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Expand Up @@ -206,6 +206,12 @@ static void gc_helper_get_regs(gc_helper_regs_t arr) {

#endif // MICROPY_GCREGS_SETJMP

#ifdef USE_YK
void gc_collect_shadowstack(void *start, void *end) {
gc_collect_root(start, ((intptr_t) end - (intptr_t) start) / sizeof(void *));
}
#endif

// Explicitly mark this as noinline to make sure the regs variable
// is effectively at the top of the stack: otherwise, in builds where
// LTO is enabled and a lot of inlining takes place we risk a stack
Expand All @@ -217,6 +223,16 @@ MP_NOINLINE void gc_helper_collect_regs_and_stack(void) {
// GC stack (and regs because we captured them)
void **regs_ptr = (void **)(void *)&regs;
gc_collect_root(regs_ptr, ((uintptr_t)MP_STATE_THREAD(stack_top) - (uintptr_t)&regs) / sizeof(uintptr_t));

#ifdef USE_YK
// Now scan the shadow stack.
//
// FIXME: this will scan the shadow stacks of *all* threads, but we should
// probably only scan the current thread's shadow stack here. yk doesn't
// currently have provide an API (e.g. a `yk_curthread_sstack_bounds()`)
// that could enable this.
yk_foreach_shadowstack(gc_collect_shadowstack);
#endif
}

#endif // MICROPY_ENABLE_GC