On 11/24/2015 10:14 PM, Segher Boessenkool wrote: >> However, there is still a subtle difference for non-static objects. >> Adding the initializer turns a tentative definition into a definite one, >> and it seems that this can't go into .bss. > > extern int a; > int a = 0; > > and > > int b; > int b = 0; > > go to .bss just fine. Did you mean something different? This is what I meant. I still see a subtle difference in the generated executable, but it is not what I thought. One should be using proper tools. This is the diff after adding a couple of zero initializers: @@ -810,7 +810,7 @@ 00000000003958f8 d __elf_set___libc_thread_subfreeres_element___rpc_thread_destroy__ 00000000003958e8 d __elf_set___libc_thread_subfreeres_element_strerror_thread_freeres__ 00000000001699a0 r empty_path_elem -000000000039ea00 b _end +000000000039e9f8 b _end 00000000000fd6a0 T endaliasent 00000000000dfaa0 T endfsent 00000000000b3690 T endgrent @@ -1287,14 +1287,14 @@ 00000000000216c0 T __gconv_get_modules_db 0000000000022d10 t __gconv_get_path 0000000000028c00 t __gconv_load_cache -000000000039e378 b __gconv_lock +000000000039a8e8 b __gconv_lock 0000000000028eb0 t __gconv_lookup_cache -000000000039e388 b __gconv_max_path_elem_len +000000000039e380 b __gconv_max_path_elem_len 00000000001620a9 r gconv_module_ext -000000000039e380 b __gconv_modules_db +000000000039e378 b __gconv_modules_db 0000000000020f20 t __gconv_open -000000000039e398 b __gconv_path_elem -000000000039e390 b __gconv_path_envvar +000000000039e390 b __gconv_path_elem +000000000039e388 b __gconv_path_envvar 00000000000230f0 t __gconv_read_conf 0000000000029310 t __gconv_release_cache 00000000000293c0 t __gconv_release_shlib @@ -3412,7 +3412,7 @@ 0000000000397920 d __libc_utmp_file_functions 000000000039a438 d __libc_utmp_file_name 000000000039a430 d __libc_utmp_jump_table -000000000039e9f8 b __libc_utmp_lock +000000000039e164 b __libc_utmp_lock 00000000003978e0 d __libc_utmp_unknown_functions 000000000007a350 T __libc_valloc 00000000001656d0 r __libc_version @@ -4155,7 +4155,7 @@ 000000000039b880 b old_realloc_hook 000000000011b980 t __old_realpath 000000000039bad0 b old_tz -000000000039a8e8 b once +000000000039a8ec b once 000000000039d77c b once.11214 000000000039dae4 b once.13803 000000000039bf64 b once.14680 So __gconv_lock moves towards the end, somehow improving the overall shared object size: 1659534 20312 17192 1697038 19e50e build-pristine/libc.so.6 1659534 20312 17184 1697030 19e506 build/libc.so.6 (In the diff above, - is the pristine variant (without initializer) and + has the initializer.) Anyway, it means I can submit my patch because the GCC optimization does what we need. Thanks, Florian
