A runtime non-symbolic traceback is a list of addresses of call instructions.
To enable this feature you must use the -E
gnatbind's option. With this option a stack traceback is stored as part
of exception information. It is possible to retrieve this information using the
Let's have a look at a simple example:
|procedure STB is procedure P1 is begin raise Constraint_Error; end P1; procedure P2 is begin P1; end P2; begin P2; end STB;|
$ gnatmake stb -bargs -E $ stb Execution terminated by unhandled exception Exception name: CONSTRAINT_ERROR Message: stb.adb:5 Call stack traceback locations: 0x401373 0x40138b 0x40139c 0x401335 0x4011c4 0x4011f1 0x77e892a4
As we see the traceback lists a sequence of addresses for the unhandled
CONSTRAINT_ERROR raised in procedure P1. It is easy to
guess that this exception come from procedure P1. To translate these
addresses into the source lines where the calls appear, the
addr2line tool, described below, is invaluable. The use of this tool
requires the program to be compiled with debug information.
$ gnatmake -g stb -bargs -E $ stb Execution terminated by unhandled exception Exception name: CONSTRAINT_ERROR Message: stb.adb:5 Call stack traceback locations: 0x401373 0x40138b 0x40139c 0x401335 0x4011c4 0x4011f1 0x77e892a4 $ addr2line --exe=stb 0x401373 0x40138b 0x40139c 0x401335 0x4011c4 0x4011f1 0x77e892a4 00401373 at d:/stb/stb.adb:5 0040138B at d:/stb/stb.adb:10 0040139C at d:/stb/stb.adb:14 00401335 at d:/stb/b~stb.adb:104 004011C4 at /build/.../crt1.c:200 004011F1 at /build/.../crt1.c:222 77E892A4 in ?? at ??:0
addr2line has a number of other useful options:
$ addr2line --exe=stb --functions --demangle=gnat 0x401373 0x40138b 0x40139c 0x401335 0x4011c4 0x4011f1 00401373 in stb.p1 at d:/stb/stb.adb:5 0040138B in stb.p2 at d:/stb/stb.adb:10 0040139C in stb at d:/stb/stb.adb:14 00401335 in main at d:/stb/b~stb.adb:104 004011C4 in <__mingw_CRTStartup> at /build/.../crt1.c:200 004011F1 in <mainCRTStartup> at /build/.../crt1.c:222
From this traceback we can see that the exception was raised in stb.adb at line 5, which was reached from a procedure call in stb.adb at line 10, and so on. The b~std.adb is the binder file, which contains the call to the main program. see Running gnatbind. The remaining entries are assorted runtime routines, and the output will vary from platform to platform.
It is also possible to use
GDB with these traceback addresses to debug
the program. For example, we can break at a given code location, as reported
in the stack traceback:
$ gdb -nw stb Furthermore, this feature is not implemented inside Windows DLL. Only the non-symbolic traceback is reported in this case. (gdb) break *0x401373 Breakpoint 1 at 0x401373: file stb.adb, line 5.
It is important to note that the stack traceback addresses do not change when debug information is included. This is particularly useful because it makes it possible to release software without debug information (to minimize object size), get a field report that includes a stack traceback whenever an internal bug occurs, and then be able to retrieve the sequence of calls with the same program compiled with debug information.