fix memory leak in -E mode

[sorokin]

When running with -fsanitize=leak enabled nasm prints these errors:

Direct leak of 114 byte(s) in 10 object(s) allocated from:
    #0 0x7f3031ef0867 in __interceptor_malloc ../../../../src/libsanitizer/asan/asan_malloc_linux.cpp:145
    #1 0x564dc07a2f6c in nasm_malloc nasmlib/alloc.c:55
    #2 0x564dc07f606a in detoken asm/preproc.c:2029
    #3 0x564dc0828a62 in pp_getline asm/preproc.c:7835
    #4 0x564dc0797f3e in main asm/nasm.c:654
    #5 0x7f3031608d8f in __libc_start_call_main ../sysdeps/nptl/libc_start_call_main.h:58
    #6 0x7f3031608e3f in __libc_start_main_impl ../csu/libc-start.c:392
    #7 0x564dc0799c24 in _start (/home/ivan/d/nasm/nasm+0x2e5c24)

Direct leak of 10 byte(s) in 10 object(s) allocated from:
    #0 0x7f3031ef0867 in __interceptor_malloc ../../../../src/libsanitizer/asan/asan_malloc_linux.cpp:145
    #1 0x564dc07a2f6c in nasm_malloc nasmlib/alloc.c:55
    #2 0x564dc07f64f9 in detoken asm/preproc.c:2029
    #3 0x564dc0828a62 in pp_getline asm/preproc.c:7835
    #4 0x564dc0797f3e in main asm/nasm.c:654
    #5 0x7f3031608d8f in __libc_start_call_main ../sysdeps/nptl/libc_start_call_main.h:58
    #6 0x7f3031608e3f in __libc_start_main_impl ../csu/libc-start.c:392
    #7 0x564dc0799c24 in _start (/home/ivan/d/nasm/nasm+0x2e5c24)

This is reproducible on tests that do preprocessing for example weirdpaste test.

The problem is caused by the fact that the line returned by pp_getline isn't freed in main function.

[hpax]

Is this still a problem?

[sorokin]

I tested the latest commit 22a9118 in master and, yes, the bug is still present. The exact error message is slightly different, but I guess it is because of the newer compiler version.

In order to reproduce the problem one can run make test when nasm is configured with -fsanitize=address,undefined. Here is how I did it:

git clone git@github.com:netwide-assembler/nasm.git
cd nasm
./autogen.sh

# at first run tests normally to create the directory test/golden
./configure
make
make test # tests print a lot of errors, but this is because we have no directory test/golden yet
# tests created the directory test/testresults, rename it as test/golden
mv test/testresults test/golden

# now run the tests under the sanitizers
make clean # make clean is important here, as the build system doesn't rebuild when compiler flags are changed!
CFLAGS="-fsanitize=address,undefined -g" ./configure
make
make test
# now observe a lot of mismatches of stderr files

In this specific bug the problematic file is test/testresults/weirdpaste/preproc/stderr. On my machin the specific output is:

==996926==ERROR: LeakSanitizer: detected memory leaks

Direct leak of 124 byte(s) in 20 object(s) allocated from:
    #0 0x7e96126fd9c7 in malloc ../../../../src/libsanitizer/asan/asan_malloc_linux.cpp:69
    #1 0x55a08fa0f6b5 in nasm_malloc nasmlib/alloc.c:25
    #2 0x55a08f90db3a in detoken asm/preproc.c:2219
    #3 0x55a08f949b38 in pp_getline asm/preproc.c:8815
    #4 0x55a08f8ab33e in main asm/nasm.c:602
    #5 0x7e9611a2a1c9 in __libc_start_call_main ../sysdeps/nptl/libc_start_call_main.h:58
    #6 0x7e9611a2a28a in __libc_start_main_impl ../csu/libc-start.c:360
    #7 0x55a08f8a6e84 in _start (/mnt/c/w/projects/nasm/nasm+0x34be84) (BuildId: d3f329ecc664d9645b45338a0a54df158f5195dc)

SUMMARY: AddressSanitizer: 124 byte(s) leaked in 20 allocation(s).

So, essentially the same problem as I reported originally.

[sorokin]

I rebased the patch so it applies cleanly to the latest master. I also retested the patch and I can confirm that without it the test/testresults/weirdpaste/preproc/stderr shows the memory leaks and with the patch the test passes cleanly.