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/**************************************************************************/
/* */
/* OCaml */
/* */
/* KC Sivaramakrishnan, Indian Institute of Technology, Madras */
/* Tom Kelly, OCaml Labs Consultancy */
/* Stephen Dolan, University of Cambridge */
/* */
/* Copyright 2021 Indian Institute of Technology, Madras */
/* Copyright 2021 OCaml Labs Consultancy */
/* Copyright 2019 University of Cambridge */
/* */
/* All rights reserved. This file is distributed under the terms of */
/* the GNU Lesser General Public License version 2.1, with the */
/* special exception on linking described in the file LICENSE. */
/* */
/**************************************************************************/
#define CAML_INTERNALS
#include "caml/config.h"
#include <string.h>
#ifdef HAS_UNISTD
#include <unistd.h>
#endif
#include <assert.h>
#include "caml/alloc.h"
#include "caml/callback.h"
#include "caml/codefrag.h"
#include "caml/fail.h"
#include "caml/fiber.h"
#include "caml/gc_ctrl.h"
#include "caml/platform.h"
#include "caml/minor_gc.h"
#include "caml/misc.h"
#include "caml/major_gc.h"
#include "caml/memory.h"
#include "caml/startup_aux.h"
#ifdef NATIVE_CODE
#include "caml/stack.h"
#include "caml/frame_descriptors.h"
#endif
#ifdef USE_MMAP_MAP_STACK
#include <sys/mman.h>
#endif
#ifdef DEBUG
#define fiber_debug_log(...) caml_gc_log(__VA_ARGS__)
#else
#define fiber_debug_log(...)
#endif
static_assert(sizeof(struct stack_info) == Stack_ctx_words * sizeof(value), "");
static _Atomic int64_t fiber_id = 0;
uintnat caml_get_init_stack_wsize (void)
{
uintnat default_stack_wsize = Wsize_bsize(Stack_init_bsize);
uintnat stack_wsize;
if (default_stack_wsize < caml_max_stack_wsize)
stack_wsize = default_stack_wsize;
else
stack_wsize = caml_max_stack_wsize;
return stack_wsize;
}
void caml_change_max_stack_size (uintnat new_max_wsize)
{
struct stack_info *current_stack = Caml_state->current_stack;
asize_t wsize = Stack_high(current_stack) - (value*)current_stack->sp
+ Stack_threshold / sizeof (value);
if (new_max_wsize < wsize) new_max_wsize = wsize;
if (new_max_wsize != caml_max_stack_wsize){
caml_gc_log ("Changing stack limit to %"
ARCH_INTNAT_PRINTF_FORMAT "uk bytes",
new_max_wsize * sizeof (value) / 1024);
}
caml_max_stack_wsize = new_max_wsize;
}
#define NUM_STACK_SIZE_CLASSES 5
struct stack_info** caml_alloc_stack_cache (void)
{
struct stack_info** stack_cache =
(struct stack_info**)caml_stat_alloc_noexc(sizeof(struct stack_info*) *
NUM_STACK_SIZE_CLASSES);
if (stack_cache == NULL)
return NULL;
for (int i = 0; i < NUM_STACK_SIZE_CLASSES; i++)
stack_cache[i] = NULL;
return stack_cache;
}
Caml_inline struct stack_info* alloc_for_stack (mlsize_t wosize)
{
size_t stack_len = sizeof(struct stack_info) + sizeof(value) * wosize;
size_t len;
/* Some platforms require 16-byte alignment of the stack pointer, which
will be _at the end_ of this allocation, so we need to ask for a bit more
memory to make sure that
caml_round_up(allocated stack base + stack_len, 16) + sizeof handler
will fit the allocated space.
When using mmap, we can rely upon the stack base being page-aligned
and thus aligned to a 16 byte boundary, and can round up here;
otherwise we need to always ask for 15 more bytes in order to cope with
all misalignment possibilities, even though it is likely that the
result of caml_stat_alloc_noexc() will be at least aligned to an
8-byte boundary. */
#ifdef USE_MMAP_MAP_STACK
len = caml_round_up(stack_len, 16) + sizeof(struct stack_handler);
#else
len = stack_len + (16 - 1) + sizeof(struct stack_handler);
#endif
#ifdef USE_MMAP_MAP_STACK
struct stack_info* si;
si = mmap(NULL, len, PROT_WRITE | PROT_READ,
MAP_ANONYMOUS | MAP_PRIVATE | MAP_STACK, -1, 0);
if (si == MAP_FAILED)
return NULL;
si->size = len;
return si;
#else
return caml_stat_alloc_noexc(len);
#endif /* USE_MMAP_MAP_STACK */
}
/* Returns the index into the [Caml_state->stack_cache] array if this size is
* pooled. If unpooled, it is [-1].
*
* Stacks may be unpooled if either the stack size is not 2**N multiple of
* [caml_fiber_wsz] or the stack is bigger than pooled sizes. */
Caml_inline int stack_cache_bucket (mlsize_t wosize) {
mlsize_t size_bucket_wsz = caml_fiber_wsz;
int bucket=0;
while (bucket < NUM_STACK_SIZE_CLASSES) {
if (wosize == size_bucket_wsz)
return bucket;
++bucket;
size_bucket_wsz += size_bucket_wsz;
}
return -1;
}
static struct stack_info*
alloc_size_class_stack_noexc(mlsize_t wosize, int cache_bucket, value hval,
value hexn, value heff, int64_t id)
{
struct stack_info* stack;
struct stack_handler* hand;
struct stack_info **cache = Caml_state->stack_cache;
static_assert(sizeof(struct stack_info) % sizeof(value) == 0, "");
static_assert(sizeof(struct stack_handler) % sizeof(value) == 0, "");
CAMLassert(cache != NULL);
if (cache_bucket != -1 &&
cache[cache_bucket] != NULL) {
stack = cache[cache_bucket];
cache[cache_bucket] =
(struct stack_info*)stack->exception_ptr;
CAMLassert(stack->cache_bucket == stack_cache_bucket(wosize));
hand = stack->handler;
} else {
/* couldn't get a cached stack, so have to create one */
stack = alloc_for_stack(wosize);
if (stack == NULL) {
return NULL;
}
stack->cache_bucket = cache_bucket;
/* Ensure 16-byte alignment because some architectures (e.g. arm64)
require it. alloc_for_stack() has allocated extra room to prevent
this computation from overflowing. */
hand = (struct stack_handler*)caml_round_up(
(uintnat)stack + sizeof(struct stack_info) + sizeof(value) * wosize, 16);
stack->handler = hand;
}
hand->handle_value = hval;
hand->handle_exn = hexn;
hand->handle_effect = heff;
hand->parent = NULL;
stack->sp = (value*)hand;
stack->exception_ptr = NULL;
stack->id = id;
#ifdef DEBUG
stack->magic = 42;
#endif
/* Due to stack alignment performed above, the actual stack size may be
* larger than requested. */
CAMLassert(Stack_high(stack) - Stack_base(stack) >= wosize);
return stack;
}
/* allocate a stack with at least "wosize" usable words of stack */
struct stack_info*
caml_alloc_stack_noexc(mlsize_t wosize, value hval, value hexn, value heff,
int64_t id)
{
int cache_bucket = stack_cache_bucket (wosize);
return alloc_size_class_stack_noexc(wosize, cache_bucket, hval, hexn, heff,
id);
}
#ifdef NATIVE_CODE
value caml_alloc_stack (value hval, value hexn, value heff) {
const int64_t id = atomic_fetch_add(&fiber_id, 1);
struct stack_info* stack =
alloc_size_class_stack_noexc(caml_fiber_wsz, 0 /* first bucket */,
hval, hexn, heff, id);
if (!stack) caml_raise_out_of_memory();
fiber_debug_log ("Allocate stack=%p of %" ARCH_INTNAT_PRINTF_FORMAT
"u words", stack, caml_fiber_wsz);
return Val_ptr(stack);
}
void caml_get_stack_sp_pc (struct stack_info* stack,
char** sp /* out */, uintnat* pc /* out */)
{
char* p = (char*)stack->sp;
p = First_frame(p);
*pc = Saved_return_address(p); /* ret addr */
*sp = p; /* pointer to first frame */
}
Caml_inline void scan_stack_frames(
scanning_action f, scanning_action_flags fflags, void* fdata,
struct stack_info* stack, value* gc_regs)
{
char * sp;
uintnat retaddr;
value * regs;
frame_descr * d;
int n, ofs;
unsigned short * p;
value *root;
caml_frame_descrs * fds = caml_get_frame_descrs();
sp = (char*)stack->sp;
regs = gc_regs;
next_chunk:
if (sp == (char*)Stack_high(stack)) return;
sp = First_frame(sp);
retaddr = Saved_return_address(sp);
while(1) {
d = caml_find_frame_descr(fds, retaddr);
CAMLassert(d);
if (!frame_return_to_C(d)) {
/* Scan the roots in this frame */
for (p = d->live_ofs, n = d->num_live; n > 0; n--, p++) {
ofs = *p;
if (ofs & 1) {
root = regs + (ofs >> 1);
} else {
root = (value *)(sp + ofs);
}
f (fdata, *root, root);
}
/* Move to next frame */
sp += frame_size(d);
retaddr = Saved_return_address(sp);
/* XXX KC: disabled already scanned optimization. */
} else {
/* This marks the top of an ML stack chunk. Move sp to the previous
* stack chunk. */
regs = Saved_gc_regs(sp); /* update gc_regs */
sp += Stack_header_size; /* skip trap frame, gc_regs, DWARF pointer */
goto next_chunk;
}
}
}
void caml_scan_stack(
scanning_action f, scanning_action_flags fflags, void* fdata,
struct stack_info* stack, value* gc_regs)
{
while (stack != NULL) {
scan_stack_frames(f, fflags, fdata, stack, gc_regs);
f(fdata, Stack_handle_value(stack), &Stack_handle_value(stack));
f(fdata, Stack_handle_exception(stack), &Stack_handle_exception(stack));
f(fdata, Stack_handle_effect(stack), &Stack_handle_effect(stack));
stack = Stack_parent(stack);
}
}
void caml_maybe_expand_stack (void)
{
struct stack_info* stk = Caml_state->current_stack;
uintnat stack_available =
(value*)stk->sp - Stack_base(stk);
uintnat stack_needed =
Stack_threshold / sizeof(value)
+ 8 /* for words pushed by caml_start_program */;
if (stack_available < stack_needed)
if (!caml_try_realloc_stack (stack_needed))
caml_raise_stack_overflow();
if (Caml_state->gc_regs_buckets == NULL) {
/* Ensure there is at least one gc_regs bucket available before
running any OCaml code. See fiber.h for documentation. */
value* bucket = caml_stat_alloc(sizeof(value) * Wosize_gc_regs);
bucket[0] = 0; /* no next bucket */
Caml_state->gc_regs_buckets = bucket;
}
}
#else /* End NATIVE_CODE, begin BYTE_CODE */
value caml_global_data;
CAMLprim value caml_alloc_stack(value hval, value hexn, value heff)
{
value* sp;
const int64_t id = atomic_fetch_add(&fiber_id, 1);
struct stack_info* stack =
alloc_size_class_stack_noexc(caml_fiber_wsz, 0 /* first bucket */,
hval, hexn, heff, id);
if (!stack) caml_raise_out_of_memory();
sp = Stack_high(stack);
sp -= 1;
sp[0] = Val_long(1);
stack->sp = sp;
return Val_ptr(stack);
}
CAMLprim value caml_ensure_stack_capacity(value required_space)
{
asize_t req = Long_val(required_space);
if (Caml_state->current_stack->sp - req <
Stack_base(Caml_state->current_stack))
if (!caml_try_realloc_stack(req))
caml_raise_stack_overflow();
return Val_unit;
}
/*
Root scanning.
Used by the GC to find roots on the stacks of running or runnable fibers.
*/
/* Code pointers are stored on the bytecode stack as naked pointers.
We must avoid passing them to the scanning action,
unless we know that it is a no-op outside young values
(so it will safely ignore code pointers). */
Caml_inline int is_scannable(scanning_action_flags flags, value v) {
return
(flags & SCANNING_ONLY_YOUNG_VALUES)
|| (Is_block(v) && caml_find_code_fragment_by_pc((char *) v) == NULL);
}
void caml_scan_stack(
scanning_action f, scanning_action_flags fflags, void* fdata,
struct stack_info* stack, value* v_gc_regs)
{
value *low, *high;
while (stack != NULL) {
CAMLassert(stack->magic == 42);
high = Stack_high(stack);
low = stack->sp;
for (value *sp = low; sp < high; sp++) {
value v = *sp;
if (is_scannable(fflags, v)) {
f(fdata, v, sp);
}
}
if (is_scannable(fflags, Stack_handle_value(stack)))
f(fdata, Stack_handle_value(stack), &Stack_handle_value(stack));
if (is_scannable(fflags, Stack_handle_exception(stack)))
f(fdata, Stack_handle_exception(stack), &Stack_handle_exception(stack));
if (is_scannable(fflags, Stack_handle_effect(stack)))
f(fdata, Stack_handle_effect(stack), &Stack_handle_effect(stack));
stack = Stack_parent(stack);
}
}
#endif /* end BYTE_CODE */
/*
Stack management.
Used by the interpreter to allocate stack space.
*/
#ifdef NATIVE_CODE
/* Update absolute exception pointers for new stack*/
void caml_rewrite_exception_stack(struct stack_info *old_stack,
value** exn_ptr, struct stack_info *new_stack)
{
fiber_debug_log("Old [%p, %p]", Stack_base(old_stack), Stack_high(old_stack));
fiber_debug_log("New [%p, %p]", Stack_base(new_stack), Stack_high(new_stack));
if(exn_ptr) {
fiber_debug_log ("*exn_ptr=%p", *exn_ptr);
while (Stack_base(old_stack) < *exn_ptr &&
*exn_ptr <= Stack_high(old_stack)) {
#ifdef DEBUG
value* old_val = *exn_ptr;
#endif
*exn_ptr = Stack_high(new_stack) - (Stack_high(old_stack) - *exn_ptr);
fiber_debug_log ("Rewriting %p to %p", old_val, *exn_ptr);
CAMLassert(Stack_base(new_stack) < *exn_ptr);
CAMLassert((value*)*exn_ptr <= Stack_high(new_stack));
exn_ptr = (value**)*exn_ptr;
}
fiber_debug_log ("finished with *exn_ptr=%p", *exn_ptr);
} else {
fiber_debug_log ("exn_ptr is null");
}
}
#ifdef WITH_FRAME_POINTERS
/* Update absolute base pointers for new stack */
static void rewrite_frame_pointers(struct stack_info *old_stack,
struct stack_info *new_stack)
{
struct frame_walker {
struct frame_walker *base_addr;
uintnat return_addr;
};
ptrdiff_t delta;
delta = (char*)Stack_high(new_stack) - (char*)Stack_high(old_stack);
/* Walk the frame-pointers linked list */
for (struct frame_walker *frame = __builtin_frame_address(0), *next;
frame;
frame = next) {
void *top, **p;
top = (char*)&frame->return_addr
+ 1 * sizeof(value) /* return address */
+ 2 * sizeof(value) /* trap frame */
+ 2 * sizeof(value); /* DWARF pointer & gc_regs */
/* Detect top of the fiber and bail out */
/* It also avoid to dereference invalid base pointer at main */
if (top == Stack_high(old_stack))
break;
/* Save the base address since it may be adjusted */
next = frame->base_addr;
if (!(Stack_base(old_stack) <= (value*)frame->base_addr
&& (value*)frame->base_addr < Stack_high(old_stack))) {
/* No need to adjust base pointers that don't point into the reallocated
* fiber */
continue;
}
if (Stack_base(old_stack) <= (value*)&frame->base_addr
&& (value*)&frame->base_addr < Stack_high(old_stack)) {
/* The base pointer itself is located inside the reallocated fiber
* and needs to be adjusted on the new fiber */
p = (void**)((char*)Stack_high(new_stack) - (char*)Stack_high(old_stack)
+ (char*)&frame->base_addr);
CAMLassert(*p == frame->base_addr);
*p += delta;
}
else {
/* Base pointers on other stacks are adjusted in place */
frame->base_addr = (struct frame_walker*)((char*)frame->base_addr
+ delta);
}
}
}
#endif
#endif
int caml_try_realloc_stack(asize_t required_space)
{
struct stack_info *old_stack, *new_stack;
asize_t wsize;
int stack_used;
CAMLnoalloc;
old_stack = Caml_state->current_stack;
stack_used = Stack_high(old_stack) - (value*)old_stack->sp;
wsize = Stack_high(old_stack) - Stack_base(old_stack);
uintnat max_stack_wsize = caml_max_stack_wsize;
do {
if (wsize >= max_stack_wsize) return 0;
wsize *= 2;
} while (wsize < stack_used + required_space);
if (wsize > 4096 / sizeof(value)) {
caml_gc_log ("Growing stack to %"
ARCH_INTNAT_PRINTF_FORMAT "uk bytes",
(uintnat) wsize * sizeof(value) / 1024);
} else {
caml_gc_log ("Growing stack to %"
ARCH_INTNAT_PRINTF_FORMAT "u bytes",
(uintnat) wsize * sizeof(value));
}
new_stack = caml_alloc_stack_noexc(wsize,
Stack_handle_value(old_stack),
Stack_handle_exception(old_stack),
Stack_handle_effect(old_stack),
old_stack->id);
if (!new_stack) return 0;
memcpy(Stack_high(new_stack) - stack_used,
Stack_high(old_stack) - stack_used,
stack_used * sizeof(value));
new_stack->sp = Stack_high(new_stack) - stack_used;
Stack_parent(new_stack) = Stack_parent(old_stack);
#ifdef NATIVE_CODE
caml_rewrite_exception_stack(old_stack, (value**)&Caml_state->exn_handler,
new_stack);
#ifdef WITH_FRAME_POINTERS
rewrite_frame_pointers(old_stack, new_stack);
#endif
#endif
/* Update stack pointers in Caml_state->c_stack. It is possible to have
* multiple c_stack_links to point to the same stack since callbacks are run
* on existing stacks. */
{
for (struct c_stack_link *link = Caml_state->c_stack;
link != NULL;
link = link->prev) {
if (link->stack == old_stack) {
link->stack = new_stack;
link->sp = (void*)((char*)Stack_high(new_stack) -
((char*)Stack_high(old_stack) - (char*)link->sp));
}
}
}
caml_free_stack(old_stack);
Caml_state->current_stack = new_stack;
return 1;
}
struct stack_info* caml_alloc_main_stack (uintnat init_wsize)
{
const int64_t id = atomic_fetch_add(&fiber_id, 1);
struct stack_info* stk =
caml_alloc_stack_noexc(init_wsize, Val_unit, Val_unit, Val_unit, id);
return stk;
}
void caml_free_stack (struct stack_info* stack)
{
CAMLnoalloc;
struct stack_info** cache = Caml_state->stack_cache;
CAMLassert(stack->magic == 42);
CAMLassert(cache != NULL);
if (stack->cache_bucket != -1) {
stack->exception_ptr =
(void*)(cache[stack->cache_bucket]);
cache[stack->cache_bucket] = stack;
#ifdef DEBUG
memset(Stack_base(stack), 0x42,
(Stack_high(stack)-Stack_base(stack))*sizeof(value));
#endif
} else {
#ifdef DEBUG
memset(stack, 0x42, (char*)stack->handler - (char*)stack);
#endif
#ifdef USE_MMAP_MAP_STACK
munmap(stack, stack->size);
#else
caml_stat_free(stack);
#endif
}
}
void caml_free_gc_regs_buckets(value *gc_regs_buckets)
{
while (gc_regs_buckets != NULL) {
value *next = (value*)gc_regs_buckets[0];
caml_stat_free(gc_regs_buckets);
gc_regs_buckets = next;
}
}
CAMLprim value caml_continuation_use_noexc (value cont)
{
value v;
value null_stk = Val_ptr(NULL);
CAMLnoalloc;
fiber_debug_log("cont: is_block(%d) tag_val(%ul) is_young(%d)",
Is_block(cont), Tag_val(cont), Is_young(cont));
CAMLassert(Is_block(cont));
CAMLassert(Tag_val(cont) == Cont_tag);
/* this forms a barrier between execution and any other domains
that might be marking this continuation */
if (!Is_young(cont) ) caml_darken_cont(cont);
/* at this stage the stack is assured to be marked */
v = Field(cont, 0);
if (caml_domain_alone()) {
Field(cont, 0) = null_stk;
return v;
}
if (atomic_compare_exchange_strong(Op_atomic_val(cont), &v, null_stk)) {
return v;
} else {
return null_stk;
}
}
CAMLprim value caml_continuation_use (value cont)
{
value v = caml_continuation_use_noexc(cont);
if (v == Val_ptr(NULL))
caml_raise_continuation_already_resumed();
return v;
}
CAMLprim value caml_continuation_use_and_update_handler_noexc
(value cont, value hval, value hexn, value heff)
{
value stack;
struct stack_info* stk;
stack = caml_continuation_use_noexc (cont);
stk = Ptr_val(stack);
if (stk == NULL) {
/* The continuation has already been taken */
return stack;
}
while (Stack_parent(stk) != NULL) stk = Stack_parent(stk);
Stack_handle_value(stk) = hval;
Stack_handle_exception(stk) = hexn;
Stack_handle_effect(stk) = heff;
return stack;
}
void caml_continuation_replace(value cont, struct stack_info* stk)
{
value n = Val_ptr(NULL);
int b = atomic_compare_exchange_strong(Op_atomic_val(cont), &n, Val_ptr(stk));
CAMLassert(b);
(void)b; /* squash unused warning */
}
static const value * _Atomic caml_unhandled_effect_exn = NULL;
static const value * _Atomic caml_continuation_already_resumed_exn = NULL;
static const value * cache_named_exception(const value * _Atomic * cache,
const char * name)
{
const value * exn;
exn = atomic_load_acquire(cache);
if (exn == NULL) {
exn = caml_named_value(name);
if (exn == NULL) {
fprintf(stderr, "Fatal error: exception %s\n", name);
exit(2);
}
atomic_store_release(cache, exn);
}
return exn;
}
CAMLexport void caml_raise_continuation_already_resumed(void)
{
const value * exn =
cache_named_exception(&caml_continuation_already_resumed_exn,
"Effect.Continuation_already_resumed");
caml_raise(*exn);
}
value caml_make_unhandled_effect_exn (value effect)
{
CAMLparam1(effect);
value res;
const value * exn =
cache_named_exception(&caml_unhandled_effect_exn, "Effect.Unhandled");
res = caml_alloc_small(2,0);
Field(res, 0) = *exn;
Field(res, 1) = effect;
CAMLreturn(res);
}
CAMLexport void caml_raise_unhandled_effect (value effect)
{
caml_raise(caml_make_unhandled_effect_exn(effect));
}
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