My problem is that during return of sys_execve i get a page fault
on userspace address (0x004000b0) but the pt_regs address in
do_page_fault I get is 0x8013a61c which is actually envp_init
arguement passed in execve("/bin/sh",argv_init,envp_init);
I was trying to debug where my pt_regs pointer got thrased during
do_page_fault()
I found following stuff very strange.
macro Do_FAULt(write) expands like..
#define DO_FAULT(write) \
.set noreorder; \
.set noat; \
SAVE_ALL; \
STI; \
nop; \
.set at; \
move a0, sp; \
jal do_page_fault; \
li a1, write; \
nop; \
j ret_from_sys_call; \
nop; \
.set noat;
this macro is called by handle_tlbx() routines.
when I tracked this problem and i observed my pt_regs address
looked o.k. and apparently right till after STI; \ and just before
instruction mfc0 a2, CP0_BADVADDR;
this i found by putting following instructions,
move a0,sp; \
jal show_regs; \
nop; \
later it jumps to do_page_fault() ,and pt_regs address there
equals unexpectedly to envp_init and from thereon everythings goes
wrong..
I also tried with negating STI; \ , but same result.
problamatic assembly code for DO_FAULT macro is following.
.set noat; \
SAVE_ALL; \
8001e694: 03a02021 move $a0,$sp ----{
8001e698: 0c03bba8 jal 800eeea0 <show_regs> my debug code of
show_regs() ...here pt_regs address is
o.k..
8001e69c: 00000000 nop ---}
8001e6a0: 40086000 mfc0 $t0,$12 -----{
8001e6a4: 3c091000 lui $t1,0x1000
8001e6a8: 3529001f ori $t1,$t1,0x1f
8001e6ac: 01094025 or $t0,$t0,$t1 STI macro code , though i
tried without STI for testing purpose, as well
8001e6b0: 3908001e xori $t0,$t0,0x1e
8001e6b4: 40886000 mtc0 $t0,$12
8001e6b8: 40064000 mfc0 $a2,$8 -----}
...
8001e6c4: 03a02021 move $a0,$sp
8001e6c8: 0c007e34 jal 8001f8d0 <do_page_fault>
-----{now in
do_page_fault() pt_regs address is erronousely
different in my case it is equal to envp_init. }
8001e6cc: 24050000 li $a1,0
8001e6d0: 00000000 nop
8001e6d4: 08006a9a j 8001aa68 <ret_from_irq>
what kind of hazard happening..?
Best Regards,
Atul
