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Re: Multiple breakpoint issue when debugging loadable kernel module
Some more info. This looks interesting.
1. find_pc_sect_symtab has changed quite a bit between the faulty
commit noted above (sha 2cdbbe44) and its parent (2cdbbe44^)!
2. Since the module is loaded into the kernel address space,
find_pc_sect_symtab seems to think the vmlinux module's symbol table
has symbol information for the function I am breaking into. Some
prints from find_pc_sect_symtab for a LKM function seems to return
vmlinux's symtab! :(
find_pc_sect_symtab(pc=0xffffffffa00d5bb8,sec=0x20fb988)
objfile=0x11cbc40, name=/usr/src/linux-cfs-bw/vmlinux
Returning 0x2690cc0 (objfile=0x11cbc40) # Which is vmlinux
So, I checked the BLOCK_START and BLOCK_END for the vmlinux image. I got this:
start=0xffffffff8102eb10
end=0xffffffffff60017f
and pc=0xffffffffa00d5bb8 was very well within start and end, so it
chose vmlinux. :(
So, I tired this (without loading vmlinux's symbols)
(gdb) target remote localhost:1234
(gdb) add-symbol-file (for module)
(gdb) info scope module_function
(got info)
(gdb) break module_function
(correct break)
(gdb) info scope module_function
(got correct info! it works!)
All locals/args info is retained.
So, to combat this, I presently do this (load vmlinux _after_ loading
module symbols)
gdb (without vmlinux)
(gdb) target remote ...
(gdb) add-symbol-file (for module)
(gdb) file vmlinux
(gdb) break vport_receive
Breakpoint 1, vport_receive (vport=0xffff880115fa7200,
skb=0xffff880117580900) at
/home/nikhilh/openvswitch/datapath/linux/vport.c:643
643 if (vport->ops->flags & VPORT_F_GEN_STATS) {
With full information.
I am also able to break into Linux functions, like sys_write for e.g.
Jan: can you try this and tell us if it works?
Thanks,
--
Vimal