(2015/03/03 22:31), Namhyung Kim wrote: > Hi Masami, > > On Mon, Mar 02, 2015 at 09:49:53PM +0900, Masami Hiramatsu wrote: >> Fix perf probe to handle aliased symbols correctly in glibc. >> In the glibc, several symbols are defined as an alias of >> __libc_XXX, e.g. malloc is an alias of __libc_malloc. >> In such cases, dwarf has no subroutine instances of the >> alias functions (e.g. no "malloc" instance), but the map >> has that symbol and its address. >> Thus, if we search the alieased symbol in debuginfo, we >> always fail to find it, but it is in the map. >> >> To solve this problem, this fails back to address-based >> alternative search, which searches the symbol in the map, >> translates its address to alternative (correct) function >> name by using debuginfo, and retry to find the alternative >> function point from debuginfo. >> >> This adds fail-back process to --vars, --lines and --add >> options. So, now you can use those on malloc@libc :) > > So this is only for binaries that have debuginfo, right? > > I have a similar issue with no debuginfo. > > $ perf probe -x /usr/lib/libc.so.6 -V calloc > The /usr/lib/libc-2.21.so file has no debug information. > Rebuild with -g, or install an appropriate debuginfo package. > Error: Failed to show vars. > > > But it also failed to add a probe to calloc: > > $ perf probe -x /usr/lib/libc.so.6 -a calloc > Failed to find symbol calloc in /usr/lib/libc-2.21.so > Error: Failed to add events. > > > Of course there's calloc in the libc binary. > > $ nm /usr/lib/libc.so.6 | grep calloc > 000000000007b1f0 t __calloc > 000000000007b1f0 T __libc_calloc > 000000000007b1f0 W calloc > > > I think the problem is that calloc is a weak symbol so it'll be > discarded during the symbol loading.
Right, I also hit same problem on waitpid, which is also an weak symbol. > It's because to avoid multiple > symbols (or aliases) at a same address so we choose a better symbol > using heuristics. But for this case I think we can allow aliases > since it's used only for finding probe points. I'm just using struct map and dso, so those should be improved. Thank you, -- Masami HIRAMATSU Software Platform Research Dept. Linux Technology Research 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/
