Created attachment 113918 [details] A test program Here is a tiny program: https://github.com/hjl-tools/simple-linux/tree/divide-by-zero Valgrind can't read its DWARF debug info with zero-size PT_LOAD segment: [hjl@gnu-cfl-1 simple-linux]$ make LD=ld.gold gcc -g -O0 -c -o test.o test.c test.c: In function \u2018main\u2019: test.c:22:9: warning: division by zero [-Wdiv-by-zero] i = 7 / 0; ^ gcc -g -c -o start.o start.S gcc -g -c -o syscall.o syscall.S ld.gold -o test test.o start.o syscall.o ./test hello world a make: *** [Makefile:12: all] Floating point exception [hjl@gnu-cfl-1 simple-linux]$ valgrind ./test ==27555== Memcheck, a memory error detector ==27555== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al. ==27555== Using Valgrind-3.13.0 and LibVEX; rerun with -h for copyright info ==27555== Command: ./test ==27555== a ==27555== ==27555== Process terminating with default action of signal 8 (SIGFPE) ==27555== Integer divide by zero at address 0x1002B95532 ==27555== at 0x40015E: ??? (in /export/ssd/git/github/simple-linux/test) ==27555== by 0x4001A8: ??? (in /export/ssd/git/github/simple-linux/test) ==27555== ==27555== HEAP SUMMARY: ==27555== in use at exit: 0 bytes in 0 blocks ==27555== total heap usage: 0 allocs, 0 frees, 0 bytes allocated ==27555== ==27555== All heap blocks were freed -- no leaks are possible ==27555== ==27555== For counts of detected and suppressed errors, rerun with: -v ==27555== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0) Floating point exception [hjl@gnu-cfl-1 simple-linux]$ gdb test GNU gdb (GDB) Fedora 8.1-19.fc28 Copyright (C) 2018 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html> This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law. Type "show copying" and "show warranty" for details. This GDB was configured as "x86_64-redhat-linux-gnu". Type "show configuration" for configuration details. For bug reporting instructions, please see: <http://www.gnu.org/software/gdb/bugs/>. Find the GDB manual and other documentation resources online at: <http://www.gnu.org/software/gdb/documentation/>. For help, type "help". Type "apropos word" to search for commands related to "word"... Reading symbols from test...done. (gdb) r Starting program: /export/ssd/git/github/simple-linux/test a Program received signal SIGFPE, Arithmetic exception. 0x000000000040015c in main (argc=1, argv=0x7fffffffd708) at test.c:22 22 i = 7 / 0; (gdb) [hjl@gnu-cfl-1 simple-linux]$ readelf -lW test Elf file type is EXEC (Executable file) Entry point 0x40019a There are 3 program headers, starting at offset 64 Program Headers: Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align LOAD 0x000000 0x0000000000400000 0x0000000000400000 0x000240 0x000240 R E 0x1000 LOAD 0x001000 0x0000000000401000 0x0000000000401000 0x000000 0x000000 RW 0x1000 GNU_STACK 0x000000 0x0000000000000000 0x0000000000000000 0x000000 0x000000 RWE 0x10 Section to Segment mapping: Segment Sections... 00 .text .rodata .eh_frame 01 .data .bss 02 [hjl@gnu-cfl-1 simple-linux]$
This is not straightforward. The segment loading code ignores zero sized segments. But the precondition for loading debuginfo is that an RX and one or two RW segments have been loaded. What I think that I need to do is add some dummy handler for zero-sized RW segments that just trigger the debuginfo loading.
(In reply to Paul Floyd from comment #1) > What I think that I need to do is add some dummy handler for zero-sized RW > segments that just trigger the debuginfo loading. I can reproduce the problem on FreeBSD. Using ld.lld I get paulf> readelf -lW test Elf file type is EXEC (Executable file) Entry point 0x20128a There are 4 program headers, starting at offset 64 Program Headers: Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align PHDR 0x000040 0x0000000000200040 0x0000000000200040 0x000118 0x000118 R 0x8 LOAD 0x000000 0x0000000000200000 0x0000000000200000 0x0001d4 0x0001d4 R 0x1000 LOAD 0x0001e0 0x00000000002011e0 0x00000000002011e0 0x0000da 0x0000da R E 0x1000 GNU_STACK 0x000000 0x0000000000000000 0x0000000000000000 0x000000 0x000000 RW 0 Section to Segment mapping: Segment Sections... 00 01 .rodata .eh_frame 02 .text 03 So this doesn't even have a zero sized RW segment. That's even worse.