Carmelo Amoroso wrote:
Colin Whittaker wrote:
Carmelo Amoroso wrote:
Try enabling debug early support into dynamic linker and run again.
Just to see if it is failing in the dynamic linker or in the application.
I suggest to build uclibc with full debug symbols too and start a real
debuggging session
with gdb.
I'd suggest to set bp in __uClibc_main (unless you are failing before entering
in this
function), and then go step by step.
I successfully debugged the ld.so in the past, so it is not impossible.
Carmelo
Thanks Carmelo,
I enabled debug early support into dynamic linker and have the same results.
I tried to break at __uClibc_main, and it segfaults before that.
Any hints on how to debug ld.so ?
Where does it get invoked ?
Colin..
Hi,
may you post the output, and readelf -a ? it may helps.
(if you prefer send me privately)
For debugging the ld.so
1) hack ld.so Makefile file to add -g to (it was removed in trunk)
2) install uclibc in a glibc/uclibc working system into a non system path
(let's say /broken/lib/)
3) compile your hello world by overriding the dynamic linker with
-Wl,--dynamic-linker,/broken/lib/ld-uClibc.so.0
4) install helloworl on the mips target
5) on the target launch gdbserver localhost:xxx ./helloworld
6) on the host, from within the source dir, launch xxx-gdb ./lib/ld-uClibc.so.0
7) connect from gdb console to the remote target as usual
8) now you can set bp in _dl_start, _dl_get_ready_to_run and so on (you cannot
step in libc.so.0, but
if you are ure something wrong happens in ld.so, that's the way)
Not a standard way, but really an interesting debugging session for what are
involved into the ld.so internals ;)
Cheers,
Carmelo
Thanks for the debugging help. That is a great trick.
So, I did this and found the segfault happens when we try to execute:
DL_BOOT_COMPUTE_GOT(got); in _dl_start() on line 195 dl-startup.c
The assembly code for that line is:
lw v0,-32736(gp)
addiu t9,v0,9476
jalr t9
nop
The data at -32736+gp = 0, so t9 = 0x2504, causing the segfault.
Looks like pretty fundamental stuff. Any thoughts ?
Colin..
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