RE: Question about kernel module debug

[Yuxin_Zhuang at emc dot com]

Sorry, the module is compiled with just '-g', no '-O2'.

> _____________________________________________ 
> From: 	Yuxin, Zhuang  
> Sent:	2007年10月16日 11:09
> To:	systemtap@sources.redhat.com
> Cc:	Yuxin, Zhuang
> Subject:	Question about kernel module debug
> 
> Hi,Systemtap users:
> 
> I've installed systemtap 0.5.8 on RHEL4 with kernel 2.6.9-42. I wanna use systemtap to debug a kernel module which is not built into the kernel and I got some questions.
> 
> 1. Is the 'debuginfo' of the module needed by systemtap is just the stuff created by gcc with option '-g'? Will an additional '-O2' make a lot of difference?
> 
> 2. I've put the '.ko' file which is built with options '-g -O2' under the proper search path and created a symbol link with the suffix '.ko.debug' to it. Before the systemtap is run, the module has been loaded and works well. But systemtap reported that it can not find the module's debuginfo. 
> The output is: 
> 
> Pass 1: parsed user script and 25 library script(s) in 80usr/10sys/136real ms.
> semantic error: cannot find module my_module debuginfo: r_offset is bogus
> semantic error: no match for probe point
> while: resolving probe point module("my_module").function("*")
> Pass 2: analyzed script: 2 probe(s), 0 function(s), 0 global(s) in 0usr/30sys/43real ms.
> Pass 2: analysis failed.  Try again with more '-v' (verbose) options.
> 
> And I straced the stap, the output before printing the error is as follows :
> 
> …...
> open("/usr/lib/systemtap/../lib/systemtap/libebl_i386.so", O_RDONLY) = -1 ENOENT (No such file or directory)
> open("/usr/lib/systemtap/libebl_i386.so", O_RDONLY) = 5
> read(5, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0`\6\0\000"..., 512) = 512
> fstat64(5, {st_mode=S_IFREG|0755, st_size=7724, ...}) = 0
> old_mmap(NULL, 10596, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 5, 0) = 0xcf5000
> old_mmap(0xcf7000, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 5, 0x1000) = 0xcf7000
> close(5)                                = 0
> open("/lib/modules/2.6.9-42.ELsmp/kernel/fs/my_module/my_module.ko.debug", O_RDONLY|O_LARGEFILE) = 5
> fcntl64(5, F_GETFL)                     = 0x8000 (flags O_RDONLY|O_LARGEFILE)
> fstat64(5, {st_mode=S_IFREG|0755, st_size=2734531, ...}) = 0
> mmap2(NULL, 2734531, PROT_READ|PROT_WRITE, MAP_PRIVATE, 5, 0) = 0xb589f000
> open("/sys/module/my_module/sections/.text", O_RDONLY) = 6
> fstat64(6, {st_mode=S_IFREG|0444, st_size=4096, ...}) = 0
> mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb589e000
> read(6, "0xd0e0c000\n", 4096)           = 11
> read(6, "", 4096)                       = 0
> close(6)                                = 0
> munmap(0xb589e000, 4096)                = 0
> open("/sys/module/my_module/sections/.rodata", O_RDONLY) = 6
> fstat64(6, {st_mode=S_IFREG|0444, st_size=4096, ...}) = 0
> mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb589e000
> read(6, "0xd0e29c90\n", 4096)           = 11
> read(6, "", 4096)                       = 0
> close(6)                                = 0
> munmap(0xb589e000, 4096)                = 0
> write(2, "semantic error: ", 16semantic error: )        = 16
> …… 
> 
> What can be the reason for the error?? 
> Any suggestions will be appreciated, thanks a lot!
> 
> 
> ZHUANG Yuxin