Java 2 Ada

How to fix GNAT symbolic traceback crash on Ubuntu

By stephane.carrez 2010-09-19 17:34:00

When you use the GNAT symbolic traceback feature with gcc 4.4 on Ubuntu 10.04, a segmentation fault occurs. This article explains why and proposes a workaround until the problem is fixed in the distribution.

Symbolic Traceback

The GNU Ada Compiler provides a support package to dump the exception traceback with symbols.

with Ada.Exceptions;
  use Ada.Exceptions;
with GNAT.Traceback.Symbolic;
  use GNAT.Traceback.Symbolic;
with Ada.Text_IO; use Ada.Text_IO;
...
exception
  when E : others =>
    Put_Line ("Exception: " & Exception_Name (E));
    Put_Line (Symbolic_Traceback (E));

GNAT Symbolic Traceback crash

On Ubuntu 10.04 and probably on other Debian distributions, the symbolic traceback crashes in convert_addresses:

Program received signal SIGSEGV, Segmentation fault.
0xb7ab20a6 in convert_addresses () from /usr/lib/libgnat-4.4.so.1
(gdb) where
#0  0xb7ab20a6 in convert_addresses () from /usr/lib/libgnat-4.4.so.1
#1  0xb7ab1f2c in gnat__traceback__symbolic__symbolic_traceback () from /usr/lib/libgnat-4.4.so.1
#2  0xb7ab2054 in gnat__traceback__symbolic__symbolic_traceback__2 () from /usr/lib/libgnat-4.4.so.1

The problem is caused by a patch that was applied on GCC 4.4 sources and which introduces a bug in convert_addresses function. Basically, the function is missing a filename argument which causes other arguments to be incorrect.

void convert_addresses (const char* filename,
         void* addrs[], int n_addr,
         char* buf, int*  len)

Since convert_addresses is provided by the libgnat-4.4.so dynamic library, we can easily replace this function by linking our program with the correct implementation. Get the convert_addresses.c, compile it and add it when you link your program:

$ gcc -c convert_addresses.c
$ gnatmake -Pproject -largs convert_addresses.o

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