Hi folks, This email is part bug report and part question. I wanted to share what I found while debugging this issue in order to helps someone that would tackle this issue in the future.
I want to retrieve the parameters of a binary that has been compile with gcc -O2 optimization option. I made a dummy program (mutatee.c in the attached archive) that contains a function named foo that has one parameter. I was wondering why I was not able to get the parameter's name, type and eventually value with my mutator program. So, I activated the DYNINST_DEBUG_DWARF=1 env var to examine what was happening. http://paste.ubuntu.com/7809741/. We can see on line 655 that there is a failure parsing the third entry of the location list for the bar variable. Here is the function foo: void __attribute__((noinline, noclone)) foo(int bar) { printf("%d",bar); return; } Using the following: objdump --dwarf=info mutatee We can find the entry for the foo function and find the bar parameter at the 0x2ec offset. <1><2cf>: Abbrev Number: 17 (DW_TAG_subprogram) <2d0> DW_AT_external : 1 <2d0> DW_AT_name : foo <2d4> DW_AT_decl_file : 1 <2d5> DW_AT_decl_line : 8 <2d6> DW_AT_prototyped : 1 <2d6> DW_AT_low_pc : 0x400650 <2de> DW_AT_high_pc : 0x13 <2e6> DW_AT_frame_base : 1 byte block: 9c (DW_OP_call_frame_cfa) <2e8> DW_AT_GNU_all_call_sites: 1 <2e8> DW_AT_sibling : <0x34b> <2><2ec>: Abbrev Number: 18 (DW_TAG_formal_parameter) <2ed> DW_AT_name : bar <2f1> DW_AT_decl_file : 1 <2f2> DW_AT_decl_line : 8 <2f3> DW_AT_type : <0x5e> <2f7> DW_AT_location : 0x0 (location list) We see at the last line that the DW_AT_location of the foo formal parameter is a location list at offset 0x0 in the loc table which we can examine using: objdump --dwarf=loc mutatee 00000000 0000000000400650 000000000040065c (DW_OP_reg5 (rdi)) 00000013 000000000040065c 0000000000400662 (DW_OP_reg1 (rdx)) 00000026 0000000000400662 0000000000400663 (DW_OP_GNU_entry_value: (DW_OP_reg5 (rdi)); DW_OP_stack_value) So from my understanding, we aren't able to correctly parse the third entry of the location list. Digging in the code I found that the keyword DW_OP_GNU_entry_value is not handle by the switch case in dwarf/src/dwarfExprParser.C:126.it then falls in the default case and then return false. This behavior causes the mutator to return an empty vector when asked for the parameters of the function. My setup: gcc version 4.8.1 (Ubuntu/Linaro 4.8.1-10ubuntu9) Dyninst branch v8.2 Is this an issue that is within Dyninst's control, more related to libdwarf or something else? Thanks, Francis
list-parameters.tar.gz
Description: GNU Zip compressed data
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