fix memory leak in elf_init

When running with -fsanitize=leak enabled nasm prints this error:

Direct leak of 31 byte(s) in 1 object(s) allocated from:
    #0 0x7faadfc56867 in __interceptor_malloc ../../../../src/libsanitizer/asan/asan_malloc_linux.cpp:145
    netwide-assembler#1 0x7faadf3ecaac in __GI___libc_scratch_buffer_dupfree malloc/scratch_buffer_dupfree.c:32
    netwide-assembler#2 0x7faadf395eed in scratch_buffer_dupfree ../include/scratch_buffer.h:147
    netwide-assembler#3 0x7faadf395eed in realpath_stk stdlib/canonicalize.c:424
    netwide-assembler#4 0x7faadf3964f5 in __GI___realpath stdlib/canonicalize.c:446
    netwide-assembler#5 0x7faadfbe6b7c in __interceptor_canonicalize_file_name ../../../../src/libsanitizer/sanitizer_common/sanitizer_common_interceptors.inc:3682
    netwide-assembler#6 0x5643cfb1b058 in nasm_realpath nasmlib/realpath.c:58
    netwide-assembler#7 0x5643cfaaaef5 in elf_init output/outelf.c:547
    netwide-assembler#8 0x5643cfaaade7 in elf32_init output/outelf.c:496
    netwide-assembler#9 0x5643cf9d1454 in main asm/nasm.c:716
    netwide-assembler#10 0x7faadf36ed8f in __libc_start_call_main ../sysdeps/nptl/libc_start_call_main.h:58
    netwide-assembler#11 0x7faadf36ee3f in __libc_start_main_impl ../csu/libc-start.c:392
    netwide-assembler#12 0x5643cf9cce04 in _start (/home/ivan/d/nasm/nasm+0x2e2e04)

Direct leak of 24 byte(s) in 1 object(s) allocated from:
    #0 0x7faadfc56867 in __interceptor_malloc ../../../../src/libsanitizer/asan/asan_malloc_linux.cpp:145
    netwide-assembler#1 0x5643cf9dcbc4 in nasm_malloc nasmlib/alloc.c:55
    netwide-assembler#2 0x5643cf9dced4 in nasm_strndup nasmlib/alloc.c:127
    netwide-assembler#3 0x5643cfb1b4e4 in nasm_dirname nasmlib/path.c:152
    netwide-assembler#4 0x5643cfaaaf4d in elf_init output/outelf.c:550
    netwide-assembler#5 0x5643cfaaade7 in elf32_init output/outelf.c:496
    netwide-assembler#6 0x5643cf9d1454 in main asm/nasm.c:716
    netwide-assembler#7 0x7faadf36ed8f in __libc_start_call_main ../sysdeps/nptl/libc_start_call_main.h:58
    netwide-assembler#8 0x7faadf36ee3f in __libc_start_main_impl ../csu/libc-start.c:392
    netwide-assembler#9 0x5643cf9cce04 in _start (/home/ivan/d/nasm/nasm+0x2e2e04)

This error is reproducible on any test that is run with -felf.

The problem is fixed by calling nasm_free appropriately. I had to
remove const from pointers because I get -Wdiscarded-qualifiers
warning otherwise, because nasm_free takes non-const pointer.

Signed-off-by: Ivan Sorokin <[email protected]>

output/outelf.c

@@ -544,10 +544,13 @@ static void elf_init(void)
         ".shstrtab", ".strtab", ".symtab", ".symtab_shndx", NULL
     };
     const char * const *p;
-    const char * cur_path = nasm_realpath(inname);
+    char *cur_path = nasm_realpath(inname);
+    char *cur_path_dirname = nasm_dirname(cur_path);
 
     strlcpy(elf_module, inname, sizeof(elf_module));
-    strlcpy(elf_dir, nasm_dirname(cur_path), sizeof(elf_dir));
+    strlcpy(elf_dir, cur_path_dirname, sizeof(elf_dir));
+    nasm_free(cur_path);
+    nasm_free(cur_path_dirname);
     sects = NULL;
     nsects = sectlen = 0;
     syms = saa_init((int32_t)sizeof(struct elf_symbol));