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exec: Allocate code_gen_prologue from code_gen_buffer

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We had a hack for arm and sparc, allocating code_gen_prologue to a
special section.  Which, honestly does no good under certain cases.
We've already got limits on code_gen_buffer_size to ensure that all
TBs can use direct branches between themselves; reuse this limit to
ensure the prologue is also reachable.

As a bonus, we get to avoid marking a page of the main executable's
data segment as executable.

Signed-off-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>
This commit is contained in:
Richard Henderson 2012-10-16 17:30:13 +10:00 committed by Blue Swirl
parent 405def1846
commit 4438c8a946
2 changed files with 12 additions and 20 deletions
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30
exec.c
View File

@ -86,22 +86,7 @@ static int nb_tbs;
/* any access to the tbs or the page table must use this lock */ /* any access to the tbs or the page table must use this lock */
spinlock_t tb_lock = SPIN_LOCK_UNLOCKED; spinlock_t tb_lock = SPIN_LOCK_UNLOCKED;
#if defined(__arm__) || defined(__sparc__) uint8_t *code_gen_prologue;
/* The prologue must be reachable with a direct jump. ARM and Sparc64
have limited branch ranges (possibly also PPC) so place it in a
section close to code segment. */
#define code_gen_section \
__attribute__((__section__(".gen_code"))) \
__attribute__((aligned (32)))
#elif defined(_WIN32) && !defined(_WIN64)
#define code_gen_section \
__attribute__((aligned (16)))
#else
#define code_gen_section \
__attribute__((aligned (32)))
#endif
uint8_t code_gen_prologue[1024] code_gen_section;
static uint8_t *code_gen_buffer; static uint8_t *code_gen_buffer;
static size_t code_gen_buffer_size; static size_t code_gen_buffer_size;
/* threshold to flush the translated code buffer */ /* threshold to flush the translated code buffer */
@ -221,7 +206,7 @@ static int tb_flush_count;
static int tb_phys_invalidate_count; static int tb_phys_invalidate_count;
#ifdef _WIN32 #ifdef _WIN32
static void map_exec(void *addr, long size) static inline void map_exec(void *addr, long size)
{ {
DWORD old_protect; DWORD old_protect;
VirtualProtect(addr, size, VirtualProtect(addr, size,
@ -229,7 +214,7 @@ static void map_exec(void *addr, long size)
} }
#else #else
static void map_exec(void *addr, long size) static inline void map_exec(void *addr, long size)
{ {
unsigned long start, end, page_size; unsigned long start, end, page_size;
@ -621,7 +606,14 @@ static inline void code_gen_alloc(size_t tb_size)
exit(1); exit(1);
} }
map_exec(code_gen_prologue, sizeof(code_gen_prologue)); /* Steal room for the prologue at the end of the buffer. This ensures
(via the MAX_CODE_GEN_BUFFER_SIZE limits above) that direct branches
from TB's to the prologue are going to be in range. It also means
that we don't need to mark (additional) portions of the data segment
as executable. */
code_gen_prologue = code_gen_buffer + code_gen_buffer_size - 1024;
code_gen_buffer_size -= 1024;
code_gen_buffer_max_size = code_gen_buffer_size - code_gen_buffer_max_size = code_gen_buffer_size -
(TCG_MAX_OP_SIZE * OPC_BUF_SIZE); (TCG_MAX_OP_SIZE * OPC_BUF_SIZE);
code_gen_max_blocks = code_gen_buffer_size / CODE_GEN_AVG_BLOCK_SIZE; code_gen_max_blocks = code_gen_buffer_size / CODE_GEN_AVG_BLOCK_SIZE;

2
tcg/tcg.h
View File

@ -616,7 +616,7 @@ TCGv_i64 tcg_const_i64(int64_t val);
TCGv_i32 tcg_const_local_i32(int32_t val); TCGv_i32 tcg_const_local_i32(int32_t val);
TCGv_i64 tcg_const_local_i64(int64_t val); TCGv_i64 tcg_const_local_i64(int64_t val);
extern uint8_t code_gen_prologue[]; extern uint8_t *code_gen_prologue;
/* TCG targets may use a different definition of tcg_qemu_tb_exec. */ /* TCG targets may use a different definition of tcg_qemu_tb_exec. */
#if !defined(tcg_qemu_tb_exec) #if !defined(tcg_qemu_tb_exec)