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修复：解决严格别名（Strict Aliasing）违规问题，提升 -O2 优化下的稳定性 #131

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修复：解决严格别名（Strict Aliasing）违规问题，提升 -O2 优化下的稳定性 #131

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258b694
fix-strict-aliasing-violation
expertamateur Sep 2, 2025
722b985
fix-strict-aliasing-violation at kvm.c
expertamateur Sep 13, 2025
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2 changes: 1 addition & 1 deletion include/device/map.h
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Original file line number Diff line number Diff line change
Expand Up @@ -19,7 +19,7 @@
#include <cpu/difftest.h>

typedef void(*io_callback_t)(uint32_t, int, bool);
uint8_t* new_space(int size);
void* new_space(int size);

typedef struct {
const char *name;
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25 changes: 25 additions & 0 deletions include/macro.h
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Expand Up @@ -108,3 +108,28 @@
ioe_write(reg, &__io_param); })

#endif

/**
* @brief 对一个变量的位模式进行类型重解释，类似于 C++20 的 std::bit_cast。
* @note 此宏使用了GCC/Clang的语句表达式扩展，以便在表达式中使用。
* @param dest_type 目标类型。
* @param src 源变量（不是指针）。
* @return 一个类型为 dest_type 的新值，其位模式与 src 相同。
*/
#if __STDC_VERSION__ >= 201112L
#define BITCAST(dest_type, src) \
({ \
_Static_assert(sizeof(dest_type) == sizeof(src), "Bitcast types must have the same size"); \
dest_type dest; \
memcpy(&dest, &src, sizeof(dest)); \
dest; \
})
#else
#define BITCAST(dest_type, src) \
({ \
assert(sizeof(dest_type) == sizeof(src) && "Bitcast types must have the same size"); \
dest_type dest; \
memcpy(&dest, &src, sizeof(dest)); \
dest; \
})
#endif
16 changes: 7 additions & 9 deletions include/memory/host.h
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Original file line number Diff line number Diff line change
Expand Up @@ -19,22 +19,20 @@
#include <common.h>

static inline word_t host_read(void *addr, int len) {
word_t ret = 0;
switch (len) {
case 1: return *(uint8_t *)addr;
case 2: return *(uint16_t *)addr;
case 4: return *(uint32_t *)addr;
IFDEF(CONFIG_ISA64, case 8: return *(uint64_t *)addr);
case 1: case 2: case 4: IFDEF(CONFIG_ISA64, case 8: )
memcpy(&ret, addr, len); break;
default: MUXDEF(CONFIG_RT_CHECK, assert(0), return 0);
}
return ret;
}

static inline void host_write(void *addr, int len, word_t data) {
switch (len) {
case 1: *(uint8_t *)addr = data; return;
case 2: *(uint16_t *)addr = data; return;
case 4: *(uint32_t *)addr = data; return;
IFDEF(CONFIG_ISA64, case 8: *(uint64_t *)addr = data; return);
IFDEF(CONFIG_RT_CHECK, default: assert(0));
case 1: case 2: case 4: IFDEF(CONFIG_ISA64, case 8: )
memcpy(addr, &data, len); return;
default: IFDEF(CONFIG_RT_CHECK, assert(0));
}
}

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18 changes: 10 additions & 8 deletions src/device/io/map.c
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Original file line number Diff line number Diff line change
Expand Up @@ -20,15 +20,17 @@

#define IO_SPACE_MAX (32 * 1024 * 1024)

static uint8_t *io_space = NULL;
static uint8_t *p_space = NULL;
static void *io_space = NULL;
static void *p_space = NULL;

uint8_t* new_space(int size) {
uint8_t *p = p_space;
// 与malloc保持一致，由调用者决定以什么方式使用这块内存
// 只要调用者不强转则不违反严格别名规则
void *new_space(int size) {
void *p = p_space;
// page aligned;
size = (size + (PAGE_SIZE - 1)) & ~PAGE_MASK;
p_space += size;
assert(p_space - io_space < IO_SPACE_MAX);
p_space = (uint8_t *)p_space + size ;
assert((uint8_t *)p_space - (uint8_t *)io_space < IO_SPACE_MAX);
return p;
}

Expand Down Expand Up @@ -57,14 +59,14 @@ word_t map_read(paddr_t addr, int len, IOMap *map) {
check_bound(map, addr);
paddr_t offset = addr - map->low;
invoke_callback(map->callback, offset, len, false); // prepare data to read
word_t ret = host_read(map->space + offset, len);
word_t ret = host_read((uint8_t *)map->space + offset, len);
return ret;
}

void map_write(paddr_t addr, int len, word_t data, IOMap *map) {
assert(len >= 1 && len <= 8);
check_bound(map, addr);
paddr_t offset = addr - map->low;
host_write(map->space + offset, len, data);
host_write((uint8_t *)map->space + offset, len, data);
invoke_callback(map->callback, offset, len, true);
}
22 changes: 16 additions & 6 deletions tools/kvm-diff/src/kvm.c
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Original file line number Diff line number Diff line change
Expand Up @@ -20,6 +20,7 @@

#include <fcntl.h>
#include <errno.h>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <linux/kvm.h>
Expand Down Expand Up @@ -238,7 +239,8 @@ static int patching() {
if (vcpu.int_wp_state == STATE_INT_INST) return 0;
vcpu.kvm_run->s.regs.regs.rsp -= 4;
uint32_t esp = va2pa(vcpu.kvm_run->s.regs.regs.rsp);
*(uint32_t *)(vm.mem + esp) = vcpu.kvm_run->s.regs.regs.rflags & ~RFLAGS_FIX_MASK;
uint32_t rflags_val = vcpu.kvm_run->s.regs.regs.rflags & ~RFLAGS_FIX_MASK;
memcpy(vm.mem + esp, &rflags_val, sizeof(rflags_val));
vcpu.kvm_run->s.regs.regs.rflags |= RFLAGS_TF;
vcpu.kvm_run->s.regs.regs.rip ++;
vcpu.kvm_run->kvm_dirty_regs = KVM_SYNC_X86_REGS;
Expand All @@ -247,15 +249,18 @@ static int patching() {
else if (vm.mem[pc] == 0x9d) { // popf
if (vcpu.int_wp_state == STATE_INT_INST) return 0;
uint32_t esp = va2pa(vcpu.kvm_run->s.regs.regs.rsp);
vcpu.kvm_run->s.regs.regs.rflags = *(uint32_t *)(vm.mem + esp) | RFLAGS_TF | 2;
uint32_t value_from_mem;
memcpy(&value_from_mem, vm.mem + esp, sizeof(value_from_mem));
vcpu.kvm_run->s.regs.regs.rflags = value_from_mem | RFLAGS_TF | 2;
vcpu.kvm_run->s.regs.regs.rsp += 4;
vcpu.kvm_run->s.regs.regs.rip ++;
vcpu.kvm_run->kvm_dirty_regs = KVM_SYNC_X86_REGS;
return 1;
}
else if (vm.mem[pc] == 0xcf) { // iret
uint32_t ret_addr = va2pa(vcpu.kvm_run->s.regs.regs.rsp);
uint32_t eip = *(uint32_t *)(vm.mem + ret_addr);
uint32_t eip = 0;
memcpy(&eip, vm.mem + ret_addr, sizeof(eip));
vcpu.entry = eip;
kvm_set_step_mode(true, eip);
vcpu.int_wp_state = STATE_IRET_INST;
Expand All @@ -266,7 +271,10 @@ static int patching() {

static void fix_push_sreg() {
uint32_t esp = va2pa(vcpu.kvm_run->s.regs.regs.rsp);
*(uint32_t *)(vm.mem + esp) &= 0x0000ffff;
uint32_t value_from_mem = 0;
memcpy(&value_from_mem, vm.mem + esp, sizeof(value_from_mem));
value_from_mem &= 0x0000ffff;
memcpy(vm.mem + esp, &value_from_mem, sizeof(value_from_mem));
}

static void patching_after(uint64_t last_pc) {
Expand Down Expand Up @@ -310,8 +318,10 @@ static void kvm_exec(uint64_t n) {
if (vcpu.int_wp_state == STATE_INT_INST) {
uint32_t eflag_offset = 8 + (vcpu.has_error_code ? 4 : 0);
uint32_t eflag_addr = va2pa(vcpu.kvm_run->s.regs.regs.rsp + eflag_offset);
*(uint32_t *)(vm.mem + eflag_addr) &= ~RFLAGS_FIX_MASK;

uint32_t value_from_mem = 0;
memcpy(&value_from_mem, vm.mem + eflag_addr, sizeof(value_from_mem));
value_from_mem &= ~RFLAGS_FIX_MASK;
memcpy(vm.mem + eflag_addr, &value_from_mem, sizeof(value_from_mem));
Assert(vcpu.entry == vcpu.kvm_run->debug.arch.pc,
"entry not match, right = 0x%llx, wrong = 0x%x", vcpu.kvm_run->debug.arch.pc, vcpu.entry);
kvm_set_step_mode(false, 0);
Expand Down