Carmelo Amoroso wrote:
Colin Whittaker wrote:
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.
I was sure you liked it ;)
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.
so it seems that the got is not correctly set.
continue with gdb to track down why it is NULL.
Looks like pretty fundamental stuff. Any thoughts ?
Colin..
Carmelo
Well, it is 0 because the .got table is not fixed up yet when we are in
_dl_start().
The comment on line 126 of dl-startup.c says " WARNING! -- we cannot
make _any_ function calls......"
So why is the macro DL_BOOT_COMPUTE_GOT() compiled to do a jalr ?
That macro is defined as a couple of __inline__ functions for mips:
elf_machine_dynamic() and elf_mips_got_forom_gpreg().
Does one of the buildroot debug flags turn off __inline__ ? (I currently
have them all on.) If so, that is catastrophic for this function.
Is there a way to force __inline__ to work no matter the compile time
flags ?
Colin..
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