On Thu, Nov 14, 2024 at 03:58:20PM +0000, Alan Maguire wrote: > Currently, pahole relies on DWARF to find whether a particular func > has its parameter mismatched with standard or optimized away. > In both these cases, the func will not be put in BTF and this > will prevent fentry/fexit tracing for these functions. > > The current parameter checking focuses on the first location/expression > to match intended parameter register. But in some cases, the first > location/expression does not have expected matching information, > but further location like DW_OP_[GNU_]entry_value can provide > information which matches the expected parameter register. > > Patch 1 supports this; patch 2 adds locking around dwarf_getlocation* > as it is unsafe in a multithreaded environment. > > Run ~4000 times without observing a segmentation fault (as compared > to without patch 2, where a segmentation fault is observed approximately > every 200 invokations). > > Changes since v1: > > - used Eduard's approach of using a __dwarf_getlocations() > internal wrapper (Eduard, patch 1). > - renamed function to parameter__reg(); did not rename > __dwarf_getlocations() since its functionality is based around > retrieving DWARF location info rather than parameter register > indices (Yonghong, patch 2) > - added locking around dwarf_getlocation*() usage in dwarf_loader > to avoid segmentation faults reported by Eduard (Jiri, Arnaldo, > patch 2) looks good, I got 95 more functions in clang build including perf_event_read and there's no change in generated functions with gcc build Acked-by: Jiri Olsa <jolsa@xxxxxxxxxx> thanks, jirka > > Alan Maguire (1): > dwarf_loader: use libdw__lock for dwarf_getlocation(s) > > Eduard Zingerman (1): > dwarf_loader: Check DW_OP_[GNU_]entry_value for possible parameter > matching > > dwarf_loader.c | 121 +++++++++++++++++++++++++++++++++++++++---------- > 1 file changed, 96 insertions(+), 25 deletions(-) > > -- > 2.31.1 >
