Q: I've written a program that uses C++ exceptions, but instead of
catching an exception, the program prints "Abort!" and dies....
Q: When linking C++ programs, I get messages about undefined
references to __EH_FRAME_BEGIN__ and such likes. Huh?
Q: I cannot compile C++ programs that include the header
math.h: the compiler complains about redefinition of class
exception!
A: C++ exceptions were not fully supported in DJGPP before version
2.8.1 of GCC. Either upgrade to the latest version or compile with the
-fsjlj-exceptions switch to GCC. GCC support of exceptions
before v2.8.0, was minimal, so even this special switch won't work with
previous versions. If you still use GCC 2.7.2.1 and cannot upgrade, you
need to compile with the -frtti compiler switch and include the
typeinfo header in your program.
Beginning with EGCS 1.1.2 and GCC 2.95, C++ exception support requires DJGPP v2.02 or later, and will not work with v2.01 or earlier, so you might need to upgrade your DJGPP library.
Note that exception support with -fsjlj-exceptions is very slow,
since it has a significant runtime overhead, even if the exception
doesn't occur.
If you already use GCC 2.8.1, these problems could happen if you failed
to replace the specs file with the version which comes with the
GCC 2.8.1 distribution. Read the file readme.DJGPP in the GCC
distribution, for more details. GCC 2.95 and later should work with the
specs file from djdev202.zip (or later) or with the
specs file that comes with GCC itself.
Exception support in GCC is generally not stable enough yet, so you need to treat with some suspicion code produced by GCC 2.8.1 for programs that use exceptions. Latest versions of GCC support exceptions better, so upgrade to GCC 2.95 or later.
Undefined references to symbols like __EH_FRAME_BEGIN__ are a
symptom of using an old linker script djgpp.djl. You should
make sure that djgpp.djl in your lib subdirectory is from
djdevNNN.zip file that belongs to DJGPP v2.02 or later. (GCC
2.8.1 distribution required to replace djgpp.djl with a version
that came with the compiler, but the reason for that is no longer valid
with newer GCC versions, and the compiler no longer comes with
djgpp.djl. So you must restore djgpp.djl from
djdevNNN.zip.) Again, readme.DJGPP in the GCC
distribution has more on this.
If GCC complains about "Redefinition of class exception" when you
compile C++ programs which include the header math.h, you
need to replace that header. GCC 2.8.1 comes with a header
exception that conflicts with math.h from DJGPP v2.01,
which defines a struct exception. Version 2.02 of DJGPP
corrects its math.h, but if you still use v2.01, a corrected
version is included in the gcc281b.zip distribution. The
corrected math.h is installed into the
lib/gcc-lib/djgpp/2.81/include directory, so either delete or
rename the old version in the include directory, or copy the
corrected version into include. Another solution is to compile
with the -posix or -ansi compiler switch, which cause
math.h to not define struct exception.