Some problem in JOS lab3
Posted: Sun Jan 27, 2008 2:04 am
It is related to the creation of a environment (the alias of process in JOS). It need to load the static binary to the user memory and switch to run the environment from the kernel.
The code of loading the binary is like below
every time I ran into the memcpy(), there will be error like
Bochs is exiting with the following message:
[CPU0 ] exception(): 3rd (13) exception with no resolution
occurs, I guess it is the problem of writing illegal memory in memcpy.
Can you give me some suggestions. Thanks
EDIT: code tags added as per popular request -- Combuster
The code of loading the binary is like below
Code: Select all
static void
load_icode(struct Env *e, uint8_t *binary, size_t size)
{
// Hints:
// Load each program segment into virtual memory
// at the address specified in the ELF section header.
// You should only load segments with ph->p_type ==
ELF_PROG_LOAD.
// Each segment's virtual address can be found in ph->p_va
// and its size in memory can be found in ph->p_memsz.
// The ph->p_filesz bytes from the ELF binary, starting at
// 'binary + ph->p_offset', should be copied to virtual address
// ph->p_va. Any remaining memory bytes should be cleared to zero.
// (The ELF header should have ph->p_filesz <= ph->p_memsz.)
// Use functions from the previous lab to allocate and map pages.
//
// All page protection bits should be user read/write for now.
// ELF segments are not necessarily page-aligned, but you can
// assume for this function that no two segments will touch
// the same virtual page.
//
// You may find a function like segment_alloc useful.
//
// Loading the segments is much simpler if you can move data
// directly into the virtual addresses stored in the ELF binary.
// So which page directory should be in force during
// this function?
//
// Hint:
// You must also do something with the program's entry point,
// to make sure that the environment starts executing there.
// What? (See env_run() and env_pop_tf() below.)
// LAB 3: Your code here.
cprintf("Begin to load icode\n");
struct Proghdr *ph, *eph;
ph = (struct Proghdr *) (binary + ((struct Elf *)binary)->e_phoff);
eph = ph + ((struct Elf *)binary)->e_phnum;
for (; ph < eph; ph++)
{
debug("ph = %08x, eph = %08x,type=%08x\n",ph,eph,ph->p_type);
if(ph->p_type == ELF_PROG_LOAD)
{
segment_alloc(e, (void*)ph->p_va,ph->p_memsz);
memcpy((void *)ph->p_va, binary + ph->p_offset, ph->p_filesz);
debug("memmove success\n");
memset((void *)(ph->p_va + ph->p_filesz), 0x0, ph->p_memsz - ph->p_filesz);
debug("memset success\n");
}
}
//lcr3(boot_cr3);
cprintf("segment copy success\n");
// Now map one page for the program's initial stack
// at virtual address USTACKTOP - PGSIZE.
// LAB 3: Your code here.
struct Page * user_stack;
if(page_alloc(&user_stack) == -E_NO_MEM)
panic("No memory to alloc for user stack");
page_insert(e->env_pgdir, user_stack, (void *)(USTACKTOP - PGSIZE),PTE_W|PTE_U|PTE_P);
}Bochs is exiting with the following message:
[CPU0 ] exception(): 3rd (13) exception with no resolution
occurs, I guess it is the problem of writing illegal memory in memcpy.
Can you give me some suggestions. Thanks
EDIT: code tags added as per popular request -- Combuster
