[Bug binutils/25676] New: binutils can't handle the split/linked nature of the debug-records for variables whose (separate) extern-decl and definition are found in the same compilation unit

[cialdi at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=25676

            Bug ID: 25676
           Summary: binutils can't handle the split/linked nature of the
                    debug-records for variables whose (separate)
                    extern-decl and definition are found in the same
                    compilation unit
           Product: binutils
           Version: 2.33
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: binutils
          Assignee: unassigned at sourceware dot org
          Reporter: cialdi at gmail dot com
  Target Milestone: ---

let's take the following source file where g_my_externd_global is both declared
as extern and defined:

extern int g_my_externd_global;
int g_my_externd_global;
int g_my_private_global;
int main(void)
{
        g_my_externd_global=1;
        g_my_private_global=1;
        return 0;
}


what I expect is that the command 'nm -s -l' will find the filename of each
symbol and under all circumstances.

if I compile with:
gcc -g3 -gdwarf-4 -nostdlib -ffunction-sections -fdata-sections -O1 -fno-common
-c main.c -o example-O1.o

and try to get info using nm I get:
nm -s -l example-O1.o
0000000000000000 B g_my_externd_global
0000000000000000 B g_my_private_global 
/home/max/Dropbox/4202/prog/test-dwarf/main.c:3
0000000000000000 T main    /home/max/Dropbox/4202/prog/test-dwarf/main.c:4
0000000000000000 n wm4.0.446323227e5a4f4144b12e5d1860fd5e
0000000000000000 n wm4.stdcpredef.h.19.8dc41bed5d9037ff9622e015fb5f0ce3

Only one variable (g_my_private_global) has the file name and line.


change compile from -O1 to -O0:
$ gcc -g3 -gdwarf-4 -nostdlib -ffunction-sections -fdata-sections -O0
-fno-common -c main.c -o example-O0.o

$ nm -s -l example-O0.o
0000000000000000 B g_my_externd_global 
/home/max/Dropbox/4202/prog/test-dwarf/main.c:1
0000000000000000 B g_my_private_global 
/home/max/Dropbox/4202/prog/test-dwarf/main.c:3
0000000000000000 T main /home/max/Dropbox/4202/prog/test-dwarf/main.c:4
0000000000000000 n wm4.0.1c9e441054e7296bffbe77203657809a
0000000000000000 n wm4.stdcpredef.h.19.8dc41bed5d9037ff9622e015fb5f0ce3

$ gcc -g3 -gdwarf-4 -nostdlib -ffunction-sections -fdata-sections -O0
-fno-common example-O0.o -o example-O0.elf
/usr/bin/ld: warning: cannot find entry symbol _start; defaulting to
0000000000001000

$ nm -s -l example-O0.elf 
0000000000004000 B __bss_start
0000000000003f20 d _DYNAMIC
0000000000004000 B _edata
0000000000004008 B _end
0000000000004000 B g_my_externd_global
0000000000004004 B g_my_private_global 
/home/max/Dropbox/4202/prog/test-dwarf/main.c:3
0000000000002000 r __GNU_EH_FRAME_HDR
0000000000001000 T main /home/max/Dropbox/4202/prog/test-dwarf/main.c:4
                 U _start

In this case (-0O) nm can successfully retrieve filename and line for both
variables, but once linked g_my_externd_global is again without information



change compile from -fno-common to -fcommon (using -O0)

$ gcc -g3 -gdwarf-4 -nostdlib -ffunction-sections -fdata-sections -O0 -fcommon
-c main.c -o example-O0-fcommon.o

$ nm -s -l example-O0-fcommon.o
0000000000000004 C g_my_externd_global
0000000000000004 C g_my_private_global
0000000000000000 T main /home/max/Dropbox/4202/prog/test-dwarf/main.c:4
0000000000000000 n wm4.0.1c9e441054e7296bffbe77203657809a
0000000000000000 n wm4.stdcpredef.h.19.8dc41bed5d9037ff9622e015fb5f0ce3

In this case nm cannot retrieve the information for any of the variables.



tested with various versions of the tools:

$ gcc --version
gcc (Ubuntu 9.2.1-9ubuntu2) 9.2.1 20191008
Copyright (C) 2019 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

$ nm --version
GNU nm (GNU Binutils for Ubuntu) 2.33
Copyright (C) 2019 Free Software Foundation, Inc.
This program is free software; you may redistribute it under the terms of
the GNU General Public License version 3 or (at your option) any later version.
This program has absolutely no warranty.

-------------------

$ gcc --version
gcc (Ubuntu 7.5.0-3ubuntu1~18.04) 7.5.0
Copyright (C) 2017 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

$ nm --version
GNU nm (GNU Binutils for Ubuntu) 2.30
Copyright (C) 2018 Free Software Foundation, Inc.
This program is free software; you may redistribute it under the terms of
the GNU General Public License version 3 or (at your option) any later version.
This program has absolutely no warranty.

-------------------

$ arm-none-eabi-gcc --version
arm-none-eabi-gcc (GNU Tools for Arm Embedded Processors 9-2019-q4-major) 9.2.1
20191025 (release) [ARM/arm-9-branch revision 277599]
Copyright (C) 2019 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

$ arm-none-eabi-nm --version
GNU nm (GNU Tools for Arm Embedded Processors 9-2019-q4-major) 2.33.1.20191025
Copyright (C) 2019 Free Software Foundation, Inc.
This program is free software; you may redistribute it under the terms of
the GNU General Public License version 3 or (at your option) any later version.
This program has absolutely no warranty.

-------------------

$ arm-none-eabi-gcc --version
arm-none-eabi-gcc (GNU Tools for Arm Embedded Processors 8-2019-q3-update)
8.3.1 20190703 (release) [gcc-8-branch revision 273027]
Copyright (C) 2018 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

$ arm-none-eabi-nm --version
GNU nm (GNU Tools for Arm Embedded Processors 8-2019-q3-update) 2.32.0.20190703
Copyright (C) 2019 Free Software Foundation, Inc.
This program is free software; you may redistribute it under the terms of
the GNU General Public License version 3 or (at your option) any later version.
This program has absolutely no warranty.

-- 
You are receiving this mail because:
You are on the CC list for the bug.