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From: "king.chung at manchester dot ac.uk" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug debug/111740] New: Incorrect DWARF expression generated at specific live range Date: Mon, 09 Oct 2023 15:09:43 +0000 [thread overview] Message-ID: <bug-111740-4@http.gcc.gnu.org/bugzilla/> (raw) https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111740 Bug ID: 111740 Summary: Incorrect DWARF expression generated at specific live range Product: gcc Version: 12.2.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: debug Assignee: unassigned at gcc dot gnu.org Reporter: king.chung at manchester dot ac.uk Target Milestone: --- Created attachment 56080 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=56080&action=edit Source code The DWARF expression between the range 0x10984 to 0x1098c is not correct. The following is the variable I am trying to test: <5><76c>: Abbrev Number: 3 (DW_TAG_variable) <76d> DW_AT_name : (indirect string, offset: 0x436): tmp_level <771> DW_AT_decl_file : 1 <771> DW_AT_decl_line : 60 <772> DW_AT_decl_column : 17 <773> DW_AT_type : <0x641> <777> DW_AT_location : 0x1b4 (location list) 000001b4 0000000000010974 0000000000010980 (DW_OP_reg12 (a2)) 000001c7 0000000000010980 0000000000010984 (DW_OP_breg17 (a7): 0) 000001db 0000000000010984 000000000001098c (DW_OP_breg13 (a3): 0; DW_OP_breg16 (a6): 0; DW_OP_plus) 000001f2 <End of list> The following log of running the binary with GDB: +b *0x10984 Breakpoint 1 at 0x10984: file bfs.c, line 62. +continue Continuing. Breakpoint 1, 0x0000000000010984 in bfs (nodes=nodes@entry=0x9af00, edges=edges@entry=0x9bf00, starting_node=<optimized out>, level=level@entry=0xa3f08 "\177\177\177\177\177\177\001", '\177' <repeats 31 times>, level_counts=level_counts@entry=0xa4008) at bfs.c:62 +si +info registers a3 a6 a3 0xa3f08 671496 a6 0x6 6 +x 0xa3f08 0xa3f08: 0x7f7f7f7f +x 0x6 0x6: Cannot access memory at address 0x6 +print tmp_level $1 = 1 '\001' By purely using the DWARF expression, the correct value of the variable could not be found manually. Interestingly, GDB is still able to compute a value despite the DWARF expression is not correct. This again uses the same file and binary from bug111680 and bug111716 with the same command. `riscv64-unknown-linux-gnu-gcc -static -O3 -Wall -Wno-unused-label -march=rv64imafd -g -fno-reorder-blocks -o bfs bfs.c local_support.c support.c harness.c`
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