Hi Mark, first of all, thanks for giving me a direction here.
I am now trying to design the changes needed to be done in Dyninst. So far we have only used the functions dwarf_* under libdw. What I understood is that libdw is kinda divided in subsets of functions, dwarf_*, dwfl_* and dwelf_*. I didn't find any documentation about it, or the purpose of these subset of functions. (Whats fl in dwfl for?) But my understanding is that I can't use data structures from one on the other one. That alone will need some design to modify the way we parse dwarf info into Dyninst. Currently the lifetime of a dwarf handle lasts through one execution, because we parse dwarf data when the user needs it. Can you point me to more documentation here or schedule a call so I can get a more clear view of this? Regards, Sasha From: Mark Wielaard <m...@klomp.org> Sent: Saturday, June 6, 2020 9:05 AM To: Sasha Da Rocha Pinheiro <darochapi...@wisc.edu>; elfutils-devel@sourceware.org <elfutils-devel@sourceware.org> Subject: Re: location list Hi Sasha, On Sat, 2020-06-06 at 00:30 +0000, Sasha Da Rocha Pinheiro wrote: > As you can see the following variables have distinct locations: > [ 81] variable abbrev: 5 > name (string) "a" > decl_file (data1) sasha.c (1) > decl_line (data1) 12 > type (ref4) [ cd] > location (sec_offset) location list > [ 0] > [ 9f] variable abbrev: 5 > name (string) "g" > decl_file (data1) sasha.c (1) > decl_line (data1) 15 > type (ref4) [ cd] > location (sec_offset) location list > [ 4a] > [ bd] variable abbrev: 5 > name (string) "z" > decl_file (data1) sasha.c (1) > decl_line (data1) 16 > type (ref4) [ cd] > location (sec_offset) location list > [ 6e] > > But when I use the code I sent before to list the three variables, I > always get: > > [main01.cpp:73] - Variable and location found (a), size(1). > [main01.cpp:78] - interval: (0x0,0x5) > [main01.cpp:78] - interval: (0x5,0xa) > [main01.cpp:78] - interval: (0x16,0x24) > [main01.cpp:73] - Variable and location found (g), size(1). > [main01.cpp:78] - interval: (0x0,0x5) > [main01.cpp:78] - interval: (0x5,0xa) > [main01.cpp:78] - interval: (0x16,0x24) > [main01.cpp:73] - Variable and location found (z), size(1). > [main01.cpp:78] - interval: (0x0,0x5) > [main01.cpp:78] - interval: (0x5,0xa) > [main01.cpp:78] - interval: (0x16,0x24) > > > No matter the locationAttribute the code always get the first > location descriptors in .debug_loc: > > DWARF section [ 7] '.debug_loc' at offset 0x1c6: > > CU [ b] base: .text+000000000000000000 <main> > [ 0] range 0, 5 > .text+000000000000000000 <main>.. > .text+0x0000000000000004 <main+0x4> > [ 0] lit0 > [ 1] stack_value > range 5, a > .text+0x0000000000000005 <main+0x5>.. > .text+0x0000000000000009 <main+0x9> > [ 0] reg1 > range 16, 24 > .text+0x0000000000000016 <main+0x16>.. > .text+0x0000000000000023 <main+0x23> > [ 0] reg1 > [ 4a] range 0, 5 > .text+000000000000000000 <main>.. > .text+0x0000000000000004 <main+0x4> > [ 0] lit0 > [ 1] stack_value > [ 6e] range 5, a > .text+0x0000000000000005 <main+0x5>.. > .text+0x0000000000000009 <main+0x9> > [ 0] lit0 > [ 1] stack_value > range a, e > .text+0x000000000000000a <main+0xa>.. > .text+0x000000000000000d <main+0xd> > [ 0] const4u 65537 > [ 5] breg0 0 > [ 7] minus > [ 8] stack_value I think I see what is happening. The fact that <main> is at .text+000000000000000000 suggests that this is actually an ET_REL file (not linked object file). The libdw dwarf_xxx calls don't do relocations. But eu-readelf does. So while eu-readelf shows some offsets as their relocated values, your program just using dwarf_xxx calls does not. Specifically the DW_AT_location list attributes will all point to zero. Which explains why every location list seems to be the same. We don't have a public function to just apply all relocations to an object file, but opening the file through dwfl_begin () will do it. Something like the attached. Hope that helps, Mark
