Hello,
on Mips idt with Rc323334 core i have following problem.
1.After boot when the shell is execved the sequence goes like
this.
in init/main.c
execve -( macro expansion in _syscall3 in unistd. h)--> sys_execve
--> do_execve
do_execve return success and i get a sensible register dump after
do_execve(0 call in sys_execve() like,
$0 : 00000000 00000000 00000000 00000000
$4 : 00000000 00000000 00000000 00000000
$8 : 00000000 00000000 00000000 00000000
$12: 00000000 00000000 00000000 00000000
$16: 00000000 00000000 00000000 00000000
$20: 00000000 00000000 00000000 00000000
$24: 00000000 00000000
$28: 00000000 7fff7f80 00000000 00000000
epc : 004000b0
Status: 0000ff13
Cause : 00000020
EPC 004000b0 is verified by objdump of /bin/sh
STATUS 0000ff13 imply user mode and CAUSE 00000020 indicate
syscall exception..all fine.
2.but immediately after sys_execve returns the value, i get a
sudden page fault producing a imposible register dump ( epc status
and cause all zero)
Unable to handle kernel paging request at virtual address
0fc01788, epc == 00000000, ra == 00000000
Oops in fault.c:do_page_fault, line 225:
$0 : 00000000 00000000 00000000 00000000
$4 : 000072c0 800ef814 00000000 801fc000
$8 : 00000000 00000000 00000000 4c696e75
$12: 78000000 00000000 00000000 00000000
$16: 00000000 00000000 00000000 00000000
$20: 00000000 00000000 00000000 00000000
$24: 00000000 00000000
$28: 6e652900 00000000 00000000 00000000
epc : 00000000
Status: 00000000
Cause : 00000000
this i guess when sys_execve returns , stack is corrupted somehow
and regs(pointer to struct pt_regs) is no more correct.
though i haven't read fully the gcc info page and acquanited with
nasty asm code of _syscall3 in unistd.h , but does execve enters
sys_execve directly by macro expansion in _syscall3 ..or there are
relevant steps in between.?
what kind of problem i am facing ?
is this problem with saving & restoring , corruption
or in _syscall3..?
any possibility of write buffer and pipeline hazard..?
I have tried with interrupts disabled in sys_execve just for
checking prupose..
would taking support of BDI2000 kind of debuggers will be
helpful?
Best Regards,
Atul
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