Messages in this thread | | | Date | Thu, 8 Jul 2010 07:51:55 -0400 (EDT) | From | "Robert P. J. Day" <> | Subject | why can't i use gdb to dump module variables anymore? |
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trying very hard to make a long story short, documenting how to use gdb to poke around in a loaded module. the important part of the module (to demonstrate the visibility of different types of variables):
static int rpjday_1; int rpjday_2 = 20; int rpjday_3 = 30;
EXPORT_SYMBOL(rpjday_3);
once i load that module, i can see the good stuff in /proc/kallsyms:
$ grep rpjday /proc/kallsyms ffffffffa007c090 r __ksymtab_rpjday_3 [crash_gdb] ffffffffa007c0a8 r __kstrtab_rpjday_3 [crash_gdb] ffffffffa007c0a0 r __kcrctab_rpjday_3 [crash_gdb] ffffffffa007c0b4 d rpjday_2 [crash_gdb] ffffffffa007c0b8 D rpjday_3 [crash_gdb] $
i can examine the salient files under /sys/module/crash_gdb/sections/, like .data
0xffffffffa007c0b4
so here's a couple questions.
if i want to add that module's symbol table info to my running gdb session, i would use "add-symbol-file" but the first arg *must* be the address of the text section and this module has *no* .text section. so what do i use for that value? the address of the .exit.text section?
and if i try to load:
(gdb) add-symbol-file /tmp/crash_gdb.ko 0xffffffffa007c000 \ -s .data 0xffffffffa007c0b4 add symbol table from file "/tmp/crash_gdb.ko" at .text_addr = 0xffffffffa007c000 .data_addr = 0xffffffffa007c0b4 (y or n) y Reading symbols from /tmp/crash_gdb.ko...done. (gdb)
it certainly *looks* like that worked, and:
(gdb) whatis rpjday_2 type = int (gdb) whatis rpjday_3 type = int
looks good, but here's where things go wrong:
(gdb) p rpjday_2 Cannot access memory at address 0xffffffffa007c0b4 (gdb) p rpjday_3 Cannot access memory at address 0xffffffffa007c0b8
that sort of thing used to work when i was testing this on a 32-bit fedora system, but i'm now on 64-but ubuntu and i don't see why those last couple commands no longer work. the addresses certainly match what's in /proc/kallsyms, and i don't recall having to do anything special last time. have i omitted a critical compile-time option for this? thanks.
rday
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======================================================================== Robert P. J. Day Waterloo, Ontario, CANADA
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