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! > >> 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. 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). Thanks, Namhyung -- 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/