Mark JIT code as writeable / executable depending on the situation

Some platforms don't want memory to be marked as writeable and
executable at the same time. When we write to the code block, we
calculate the OS page that the buffer position maps to.  Then we call
`mprotect` to allow writes on that particular page.  As an optimization,
we cache the "last written" aligned page which allows us to amortize the
cost of the `mprotect` call.  In other words, sequential writes to the
same page will only call `mprotect` on the page once.

When we're done writing, we call `mprotect` on the entire JIT buffer.
This means we don't need to keep track of which pages were marked as
writeable, we let the OS take care of that.

Co-authored-by: John Hawthorn <john@hawthorn.email>
This commit is contained in:
Aaron Patterson 2021-10-26 16:57:30 -07:00 коммит произвёл Aaron Patterson
Родитель 94ee88b38c
Коммит 157095b3a4
6 изменённых файлов: 81 добавлений и 5 удалений

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@ -401,7 +401,7 @@ void run_runtime_tests(void)
int (*function)(void);
function = (int (*)(void))mem_block;
#define TEST(BODY) cb_set_pos(cb, 0); BODY ret(cb); assert_equal(7, function());
#define TEST(BODY) cb_set_pos(cb, 0); BODY ret(cb); cb_mark_all_executable(cb); assert_equal(7, function());
// add
TEST({ mov(cb, RAX, imm_opnd(0)); add(cb, RAX, imm_opnd(7)); })

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@ -163,7 +163,7 @@ static uint8_t *alloc_exec_mem(uint32_t mem_size)
mem_block = (uint8_t*)mmap(
(void*)req_addr,
mem_size,
PROT_READ | PROT_WRITE | PROT_EXEC,
PROT_READ | PROT_EXEC,
MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED_NOREPLACE,
-1,
0
@ -184,7 +184,7 @@ static uint8_t *alloc_exec_mem(uint32_t mem_size)
mem_block = (uint8_t*)mmap(
(void*)alloc_exec_mem,
mem_size,
PROT_READ | PROT_WRITE | PROT_EXEC,
PROT_READ | PROT_EXEC,
MAP_PRIVATE | MAP_ANONYMOUS,
-1,
0
@ -197,7 +197,7 @@ static uint8_t *alloc_exec_mem(uint32_t mem_size)
mem_block = (uint8_t*)mmap(
NULL,
mem_size,
PROT_READ | PROT_WRITE | PROT_EXEC,
PROT_READ | PROT_EXEC,
MAP_PRIVATE | MAP_ANONYMOUS,
-1,
0
@ -210,9 +210,17 @@ static uint8_t *alloc_exec_mem(uint32_t mem_size)
exit(-1);
}
codeblock_t block;
block.current_aligned_write_pos = ALIGNED_WRITE_POSITION_NONE;
block.mem_block = mem_block;
block.mem_size = mem_size;
codeblock_t * cb = &block;
// Fill the executable memory with INT3 (0xCC) so that
// executing uninitialized memory will fault
cb_mark_all_writeable(cb);
memset(mem_block, 0xCC, mem_size);
cb_mark_all_executable(cb);
return mem_block;
#else
@ -230,6 +238,7 @@ void cb_init(codeblock_t *cb, uint8_t *mem_block, uint32_t mem_size)
cb->write_pos = 0;
cb->num_labels = 0;
cb->num_refs = 0;
cb->current_aligned_write_pos = ALIGNED_WRITE_POSITION_NONE;
}
// Align the current write position to a multiple of bytes
@ -277,6 +286,7 @@ void cb_write_byte(codeblock_t *cb, uint8_t byte)
{
assert (cb->mem_block);
assert (cb->write_pos + 1 <= cb->mem_size);
cb_mark_position_writeable(cb, cb->write_pos);
cb->mem_block[cb->write_pos++] = byte;
}
@ -1771,3 +1781,35 @@ void cb_write_lock_prefix(codeblock_t *cb)
{
cb_write_byte(cb, 0xF0);
}
void cb_mark_all_writeable(codeblock_t * cb)
{
if (mprotect(cb->mem_block, cb->mem_size, PROT_READ | PROT_WRITE)) {
fprintf(stderr, "Couldn't make JIT page (%p) writeable, errno: %s", (void *)cb->mem_block, strerror(errno));
abort();
}
}
void cb_mark_position_writeable(codeblock_t * cb, uint32_t write_pos)
{
uint32_t pagesize = (uint32_t)sysconf(_SC_PAGESIZE);
uint32_t aligned_position = (write_pos / pagesize) * pagesize;
if (cb->current_aligned_write_pos != aligned_position) {
cb->current_aligned_write_pos = aligned_position;
if (mprotect(cb->mem_block + aligned_position, pagesize, PROT_READ | PROT_WRITE)) {
fprintf(stderr, "Couldn't make JIT page (%p) writeable, errno: %s", (void *)(cb->mem_block + aligned_position), strerror(errno));
abort();
}
}
}
void cb_mark_all_executable(codeblock_t * cb)
{
cb->current_aligned_write_pos = ALIGNED_WRITE_POSITION_NONE;
if (mprotect(cb->mem_block, cb->mem_size, PROT_READ | PROT_EXEC)) {
fprintf(stderr, "Couldn't make JIT page (%p) executable, errno: %s", (void *)cb->mem_block, strerror(errno));
abort();
}
}

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@ -55,8 +55,14 @@ typedef struct CodeBlock
// Flag to enable or disable comments
bool has_asm;
// Keep track of the current aligned write position.
// Used for changing protection when writing to the JIT buffer
uint32_t current_aligned_write_pos;
} codeblock_t;
// 1 is not aligned so this won't match any pages
#define ALIGNED_WRITE_POSITION_NONE 1
enum OpndType
{
OPND_NONE,
@ -261,6 +267,9 @@ static inline uint32_t cb_new_label(codeblock_t *cb, const char *name);
static inline void cb_write_label(codeblock_t *cb, uint32_t label_idx);
static inline void cb_label_ref(codeblock_t *cb, uint32_t label_idx);
static inline void cb_link_labels(codeblock_t *cb);
static inline void cb_mark_all_writeable(codeblock_t *cb);
static inline void cb_mark_position_writeable(codeblock_t *cb, uint32_t write_pos);
static inline void cb_mark_all_executable(codeblock_t *cb);
// Encode individual instructions into a code block
static inline void add(codeblock_t *cb, x86opnd_t opnd0, x86opnd_t opnd1);

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@ -4876,6 +4876,8 @@ rb_yjit_tracing_invalidate_all(void)
RUBY_ASSERT_ALWAYS(yjit_codepage_frozen_bytes <= old_pos && "frozen bytes should increase monotonically");
yjit_codepage_frozen_bytes = old_pos;
cb_mark_all_executable(ocb);
cb_mark_all_executable(cb);
RB_VM_LOCK_LEAVE();
}
@ -4957,6 +4959,7 @@ yjit_init_codegen(void)
// Generate full exit code for C func
gen_full_cfunc_return();
cb_mark_all_executable(cb);
// Map YARV opcodes to the corresponding codegen functions
yjit_reg_op(BIN(nop), gen_nop);

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@ -833,12 +833,16 @@ gen_entry_point(const rb_iseq_t *iseq, uint32_t insn_idx, rb_execution_context_t
// The entry context makes no assumptions about types
blockid_t blockid = { iseq, insn_idx };
rb_vm_barrier();
// Write the interpreter entry prologue. Might be NULL when out of memory.
uint8_t *code_ptr = yjit_entry_prologue(cb, iseq);
// Try to generate code for the entry block
block_t *block = gen_block_version(blockid, &DEFAULT_CTX, ec);
cb_mark_all_executable(ocb);
cb_mark_all_executable(cb);
// If we couldn't generate any code
if (!block || block->end_idx == insn_idx) {
return NULL;
@ -872,6 +876,8 @@ branch_stub_hit(branch_t *branch, const uint32_t target_idx, rb_execution_contex
dst_addr = branch->dst_addrs[target_idx];
}
else {
rb_vm_barrier();
// :stub-sp-flush:
// Generated code do stack operations without modifying cfp->sp, while the
// cfp->sp tells the GC what values on the stack to root. Generated code
@ -952,6 +958,9 @@ branch_stub_hit(branch_t *branch, const uint32_t target_idx, rb_execution_contex
// frame. We do that in code_for_exit_from_stub.
dst_addr = code_for_exit_from_stub;
}
cb_mark_all_executable(ocb);
cb_mark_all_executable(cb);
}
const ptrdiff_t new_branch_size = branch_code_size(branch);
@ -1201,6 +1210,7 @@ static void
invalidate_block_version(block_t *block)
{
ASSERT_vm_locking();
// TODO: want to assert that all other ractors are stopped here. Can't patch
// machine code that some other thread is running.
@ -1324,6 +1334,9 @@ invalidate_block_version(block_t *block)
yjit_runtime_counters.invalidation_count++;
#endif
cb_mark_all_executable(ocb);
cb_mark_all_executable(cb);
// fprintf(stderr, "invalidation done\n");
}

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@ -478,7 +478,7 @@ rb_yjit_compile_iseq(const rb_iseq_t *iseq, rb_execution_context_t *ec)
#if (OPT_DIRECT_THREADED_CODE || OPT_CALL_THREADED_CODE) && JIT_ENABLED
bool success = true;
RB_VM_LOCK_ENTER();
// TODO: I think we need to stop all other ractors here
rb_vm_barrier();
// Compile a block version starting at the first instruction
uint8_t *code_ptr = gen_entry_point(iseq, 0, ec);
@ -914,6 +914,8 @@ rb_yjit_iseq_mark(const struct rb_iseq_constant_body *body)
void
rb_yjit_iseq_update_references(const struct rb_iseq_constant_body *body)
{
rb_vm_barrier();
rb_darray_for(body->yjit_blocks, version_array_idx) {
rb_yjit_block_array_t version_array = rb_darray_get(body->yjit_blocks, version_array_idx);
@ -947,6 +949,11 @@ rb_yjit_iseq_update_references(const struct rb_iseq_constant_body *body)
VALUE possibly_moved = rb_gc_location(object);
// Only write when the VALUE moves, to be CoW friendly.
if (possibly_moved != object) {
// Possibly unlock the page we need to update
cb_mark_position_writeable(cb, offset_to_value);
// Object could cross a page boundary, so unlock there as well
cb_mark_position_writeable(cb, offset_to_value + SIZEOF_VALUE - 1);
memcpy(value_address, &possibly_moved, SIZEOF_VALUE);
}
}
@ -955,6 +962,8 @@ rb_yjit_iseq_update_references(const struct rb_iseq_constant_body *body)
//block->code_page = rb_gc_location(block->code_page);
}
}
cb_mark_all_executable(cb);
cb_mark_all_executable(ocb);
}
// Free the yjit resources associated with an iseq