Date: Sat, 8 Nov 2014 14:06:39 -0800 From: Shrikanth Kamath <shrikanth07@gmail.com> To: freebsd-hackers@freebsd.org, freebsd-dtrace@freebsd.org, avg@freebsd.org Subject: DTrace: stack() does not print kernel module functions for i386 Message-ID: <CAEOAkMXnwqC42gZKc0f80cppff077pYGjs5PUPht0DBcyEi8Jw@mail.gmail.com>
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I verified this on a FreeBSD 10.0 STABLE, the stack() feature does not
appear to print functions from kernel modules. I believe there is a
glitch in libdtrace in the function "dt_module_update"
(cddl/contrib/opensolaris/lib/libdtrace/common/dt_module.c).
The section header address computation which is currently being done
in the function dt_module_update for elf type ET_REL, a similar
computation needs to be done for the ET_DYN maybe. I lack background
on the elf types but for experiment sakes I changed the line
@@ -948,7 +948,7 @@ dt_module_update(dtrace_hdl_t *dtp, struct kld_fil
#if defined(__FreeBSD__)
mapbase = (uintptr_t)k_stat->address;
gelf_getehdr(dmp->dm_elf, &ehdr);
- is_elf_obj = (ehdr.e_type == ET_REL);
+ is_elf_obj = (ehdr.e_type == ET_REL) || (ehdr.e_type == ET_DYN);
if (is_elf_obj) {
dmp->dm_sec_offsets =
malloc(ehdr.e_shnum * sizeof(*dmp->dm_sec_offsets));
So from a previous run where I was running a dtrace one liner
%dtrace -n 'fbt:hwpmc:: { stack(); }'
The output without the above change shows a sample as
0 50825 pmc_find_process_descriptor:entry
0xc3c35bf5 <-- Address
not matched to symbol
kernel`syscall+0x48b
kernel`0xc0fd2121
whereas with the above nit change to include ET_DYN for section offset
adjustment I get the complete stack trace as
0 50825 pmc_find_process_descriptor:entry
hwpmc.ko`pmc_hook_handler+0x6a5 <--address matched to symbol
kernel`syscall+0x48b
kernel`0xc0fd2121
I believe without the correct section offset adjustment the following
check in the function dtrace_lookup_by_addr fails to match the address
to the correct symbol
if (addr - dmp->dm_text_va < dmp->dm_text_size ||
addr - dmp->dm_data_va < dmp->dm_data_size ||
addr - dmp->dm_bss_va < dmp->dm_bss_size)
because dml->dm_text_va was not setup correctly in dt_module_update.
Can somebody help clarify this?
Reference: commit revision 210425.
--
Shrikanth R K
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