[fortran, patch] Fix handling of backtrace options in the library

[Janne Blomqvist]

On Sat, Mar 3, 2012 at 00:35, FX <fxcoudert@gmail.com> wrote:
> Hi all,
>
> I'll offer my first patch to the new 4.8 trunk. I noticed that the -fbacktrace option and the GFORTRAN_ERROR_BACKTRACE environment variable are somewhat inconsistently handled. Currently, the environment variabled doesn't actually override the compilation option, as it should. So, I set to change that (checking both options.backtrace and compile_options.backtrace instead of only the latter) when I realized that we could improve this further by moving the checking code: it is currently located in the set_options() function, which is called from the main Fortran routine (call generated by the front-end). This means that it's not triggered if the main program is C.

Good catch!

> Full disclosure: I removed the function maybe_find_addr2line() because it's not needed anymore now the code was regrouped. However, I'll note that I don't understand why it was useful before, and that I think the comment on top of it was wrong (variable "options" could be seen in the function, it was just shadowed by the local function argument!). Thus, while I was at it, I renamed the options argument to set_options(), just to make sure we didn't have a problem of this sort in the future.

I added it because, as you say, the argument "options" in
set_options() prevented access to the global variable options, and I
was lazy and considered a new function faster than renaming the
argument. :)

> The change was bootstrapped and regtested on x86_64-apple-darwin11, but is an area not covered by the testsuite. I have manually checked that running various types of abort, both in a pure Fortran code and a mixed C/Fortran (with C main), with all combinations -fno-backtrace/GFORTRAN_ERROR_BACKTRACE, behaved as expected.

I don't think it will work if you have a C main program which then
calls _gfortran_set_options() to enable backtracing per the
mixed-language programming chapter in the manual. You probably need to
move the setup code to a separate function which is called both from
init and set_options.

Also, in the patch as it stands now, you could make find_addr2line
static and remove the prototype from libgfortran.h.  That being said,
I'd recommend moving both find_addr2line and the signal handler setup
code to backtrace.c, and then do a bit of janitorial work checking
which functions and variables can be made static.

-- 
Janne Blomqvist