(2013/12/24 16:54), Namhyung Kim wrote: > Hi Masami, > > On Mon, 23 Dec 2013 19:50:10 +0900, Masami Hiramatsu wrote: >> (2013/12/23 16:46), Namhyung Kim wrote: >>> On Mon, 23 Dec 2013 06:54:38 +0900, Masami Hiramatsu wrote: >>>> (2013/12/21 3:03), Arnaldo Carvalho de Melo wrote: >>>>> Em Fri, Dec 20, 2013 at 10:03:02AM +0000, Masami Hiramatsu escreveu: >>>> BTW, I'm not sure why debuginfo and nm shows symbol address + 0x400000, >>>> and why the perf's map/symbol can remove this offset. Could you tell me >>>> how it works? >>>> If I can get the offset (0x400000) from binary, I don't need this kind >>>> of ugly hacks... >>> >>> AFAIK the actual symbol address is what nm (and debuginfo) shows. But >>> perf adjusts symbol address to have a relative address from the start of >>> mapping (i.e. file offset) like below: >>> >>> sym.st_value -= shdr.sh_addr - shdr.sh_offset; >> >> Thanks! this is what I really need!
BTW, what I've found is that the perf's map has start, end and pgoffs but those are not initialized when we load user-binary (see dso__load_sym). I'm not sure why. >>> This way, we can handle mmap and symbol address almost uniformly >>> (i.e. ip = map->start + symbol->address). But this requires the mmap >>> event during perf record. For perf probe, we might need to synthesize >>> mapping info from the section/segment header since it doesn't have the >>> mmap event. Currently, the dso__new_map() just creates a map starts >>> from 0. >> >> I think the uprobe requires only the relative address, doesn't that? > > Yes, but fetching arguments is little different than a normal relative > address, I think. Is this for uprobe probing address? or fetching symbol(global variables)? I'd like to support uprobes probing address first. > An offset of an argument bases on the mapping address of text segment. > This fits naturally for a shared library case - base address is 0. So > we can use the symbol address (st_value) directly. But for executables, > the base address of text segment is 0x400000 on x86-64 and data symbol > is on 0x6XXXXX typically. So in this case the offset given to uprobe > should be "@+0x2XXXXX" (st_value - text_base). Oh, I see. I'd better make a testcase for checking what the best way to get such offsets. Thank you, -- Masami HIRAMATSU IT Management Research Dept. Linux Technology Center Hitachi, Ltd., Yokohama Research Laboratory E-mail: masami.hiramatsu...@hitachi.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/