如何解决为什么我在C中的以下代码中遇到了段错误？
| 我在操作系统类中有一个项目，该项目应该模拟转换后备缓冲区。 我正在写一个将在TLB丢失后调用的方法。它应该在TLB中找到下一个为空或不久没有被击中的条目，删除该条目，并将其替换为上次调用的页表中的条目。当调用该方法时，将给出页表条目中的数据。Void tlb_insert(VPAGE_NUMBER new_vpage,PAGEFRAME_NUMBER new_pframe,BOOL new_mbit,BOOL new_rbit)
{
// Starting at the clock_hand\'th entry,find first entry to
// evict with either valid bit = 0 or the R bit = 0. If there
// is no such entry,then just evict the entry pointed to by
// the clock hand.
int m;
int evct = clock_hand;
for (m = clock_hand; m < (num_tlb_entries); m++){
if (tlb[m].vbit_and_vpage & VBIT_MASK == 0 || tlb[m].mr_pframe & RBIT_MASK == 0){
evct = m;
break;
}
}
// Then,if the entry to evict has a valid bit = 1,// write the M and R bits of the of entry back to the M and R
// bitmaps,respectively,in the MMU (see mmu_modify_rbit_bitmap,etc.
// in mmu.h)
if (tlb[evct].vbit_and_vpage & VBIT_MASK == 1){
PAGEFRAME_NUMBER pfr = tlb[evct].mr_pframe & PFRAME_MASK;
int val1 = tlb[evct].mr_pframe & RBIT_MASK;
int val2 = tlb[evct].mr_pframe & MBIT_MASK;
mmu_modify_rbit_bitmap (pfr,val1);
mmu_modify_mbit_bitmap(pfr,val2);
}
// Then,insert the new vpage,pageframe,M bit,and R bit into the
// TLB entry that was just found (and possibly evicted).
tlb[evct].vbit_and_vpage = VBIT_MASK | new_vpage;
tlb[evct].mr_pframe = new_mbit | (new_rbit | new_pframe);
// Finally,set clock_hand to point to the next entry after the
// entry found above.
clock_hand = evct + 1;
}
//Writes the M & R bits in the each valid TLB
//entry back to the M & R MMU bitmaps.
void tlb_write_back()
{
int n;
for (n = 0; n < num_tlb_entries; n++){
if (tlb[n].vbit_and_vpage & VBIT_MASK == 1){
PAGEFRAME_NUMBER pfr = tlb[n].mr_pframe & PFRAME_MASK;
int val1 = tlb[n].mr_pframe & RBIT_MASK;
int val2 = tlb[n].mr_pframe & MBIT_MASK;
mmu_modify_rbit_bitmap (pfr,val1);
mmu_modify_mbit_bitmap(pfr,val2);
}
}
}
tlb[evct].vbit_and_vpage = VBIT_MASK | new_vpage;
tlb[evct].mr_pframe = new_mbit | (new_rbit | new_pframe);
解决方法
我提请您注意这张表中的
&
$ cat /usr/share/misc/operator
Operator Associativity
-------------------------------------------------------------
() [] -> . left to right
! ~ ++ -- - (type) * & sizeof new delete right to left
->* .* left to right
* / % left to right
+ - left to right
<< >> left to right
< <= > >= left to right
== != left to right
& left to right
^ left to right
| left to right
&& left to right
|| left to right
?: right to left
= += -= *= /= %= <<= >>= &= ^= |= throw right to left
?: (C++,third operand) right to left,left to right
$FreeBSD: src/share/misc/operator,v 1.2.22.1 2009/05/31 18:14:24 ed Exp $
gdb
-Wall
-g -ggdb
gdb ./yourprog
run
bt
breakpoint yourfile.c:123
print your_var_or_pointer
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