Hello,
I would like to announce that I have been able to compile GCC while
checking it with a simple MELT plugin that I have wrote. This plugin is
integrated into GCC by using the MELT plugin. I guess this is the first
successfull use of MELT with a huge real program like GCC.
For those who are not really aware about MELT and how it works:
MELT is available into 2 forms:
-A GCC branch
-A GCC plugin
Here I have use MELT as a GCC plugin.
This GCC plugin loads a melt.so library which has severals modes.
Firstly I have use the translatetomodule mode. This mode allows me to
translate my plugin (which is a file "test_fopen.melt") into several C
files and then into a dynamic test_fopen.so.
The command is the following:
gcc
-fplugin=/usr/lib64/gcc/x86_64-mandriva-linux-gnu/4.6.0/plugin/melt.so \
-fplugin-arg-melt-mode=translatetomodule \
-fplugin-arg-melt-arg=/home/mpierre/programmation/melt/test_fopen/test_fopen.melt
\
-c empty.c 2>fopen_compil_debug.txt
The second step is to compile GCC using CFLAGS which define that we use
the MELT plugin with the mode test_fopen which is defined in my plugin
and precising the location of the test_fopen.so. This allows me to
execute the pass defined in my plugin.
The command is the following:
make CFLAGS="-fplugin=/usr/lib64/gcc/x86_64-mandriva-linux-
gnu/4.6.0/plugin/melt.so -fplugin-arg-melt-mode=test_fopen
-fplugin-arg-melt-init=@@:test_fopen
-fplugin-arg-melt-module-path=$build
-fplugin-arg-melt-source-path=$build -Wno-error"
What does my test_fopen.melt plugin?
It searchs each call to the fopen function and get the lhs (under the
form of a tree).
After the fopen calls, it looks at the next gimple. If this not a
gimple_cond_equal or gimple_cond_notequal between the lhs of the call
and NULL, it returns a warning, explaining that the call was not tested.
This is not perfect for now, it can find some false positifs, in some
special cases, like this one:
s->file = fd < 0 ? F_OPEN(path, fmode) : (FILE*)fdopen(fd, fmode);
if (s->file == NULL) {
...
}
...
It comes from the fact, that at GIMPLE state, the expression is separate
into severals and the test is not made immediatly but after a few gimples.
However, it sends also some pertinents warnings:
-in gcc/gcc.c line 3422, function driver_handle_option:
There is a call to fopen without test, I don't know much about what it
does but can we be sure that the fopen always return somethings not NULL.
note: in reality this is not the fopen function but the fopen_unlocked
function which is called at this step (using a #define). I have adapted
my plugin to search also for fopen_unlocked which call fopen without
testing more the returned value.
-in libcpp/files.c line 1468, function read_name_map:
there is another call to the fopen function.
The full log of my GCC compilation can be found here:
http://pvittet.com/GSOC/log.txt .
The plugin that I have written can be found here:
https://github.com/Piervit/GMWarn/tree/master/test_fopen .
If you have any questions or remarks, I would be glad to read them :)
