Date: Sun, 9 Nov 2014 23:06:16 -0800 From: Shrikanth Kamath <shrikanth07@gmail.com> To: Rui Paulo <rpaulo@me.com> Cc: Konstantin Belousov <kostikbel@gmail.com>, freebsd-hackers@freebsd.org, freebsd-dtrace@freebsd.org, avg@freebsd.org Subject: Re: DTrace: stack() does not print kernel module functions for i386 Message-ID: <CAEOAkMVGMOFFcXvFwY9AmW_ZdtUeGVJa13g-1iWZRTXN3inG5Q@mail.gmail.com> In-Reply-To: <9011F920-3092-4E61-9CDC-68FD9092BB7D@me.com> References: <CAEOAkMXnwqC42gZKc0f80cppff077pYGjs5PUPht0DBcyEi8Jw@mail.gmail.com> <20141109093632.GV53947@kib.kiev.ua> <9011F920-3092-4E61-9CDC-68FD9092BB7D@me.com>
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On Sun, Nov 9, 2014 at 10:57 AM, Rui Paulo <rpaulo@me.com> wrote: > On Nov 9, 2014, at 01:36, Konstantin Belousov <kostikbel@gmail.com> wrote: >> >> On Sat, Nov 08, 2014 at 02:06:39PM -0800, Shrikanth Kamath wrote: >>> 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. >> >> I have no idea about DTrace guts, but can add one note you might find >> useful. >> >> From the backtace above I can conclude that your platform is i386. >> A difference between i386 and amd64 is that i386 modules are dso's >> (ET_DYN), while on amd64 modules are only linked to object files >> (ET_REL). The original author of the code probably tested on amd64. >> >> You may want to special case amd64 by #ifdef, and use ET_DYN on other >> arches. > > I agree with your analysis. I think this patch should go in with the #ifdef __amd64__ for ET_REL. > > -- > Rui Paulo > > > Thanks Konstantin/Rui, I did pull up this thread https://lists.freebsd.org/pipermail/freebsd-amd64/2010-June/013034.html where it was discussed, should I file a bug report? In any case I was trying to clarify that whether ET_DYN or ET_REL the offset adjustment needs to be done true or not? -- Shrikanth R K
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