busybox/libbb/common_bufsiz.c
Denys Vlasenko e6a2f4cc5a libbb: make bb_common_bufsiz1 1 kbyte, add capability to use bss tail for it
The config item is FEATURE_USE_BSS_TAIL. When it is off (default):

function                                             old     new   delta
read_config                                          210     228     +18
doCommands                                          2279    2294     +15
ipneigh_list_or_flush                                763     772      +9
ipaddr_list_or_flush                                1256    1261      +5
display_process_list                                1301    1306      +5
conspy_main                                         1378    1383      +5
do_lzo_compress                                      352     355      +3
do_lzo_decompress                                    565     567      +2
push                                                  46      44      -2
inetd_main                                          2136    2134      -2
uevent_main                                          421     418      -3
addLines                                              97      92      -5
bb_common_bufsiz1                                   8193    1024   -7169
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 8/5 up/down: 62/-7181)        Total: -7119 bytes
   text	   data	    bss	    dec	    hex	filename
 829850	   4086	   9080	 843016	  cdd08	busybox_old
 829901	   4086	   1904	 835891	  cc133	busybox_unstripped

FEATURE_USE_BSS_TAIL=y:

read_config                                          210     228     +18
doCommands                                          2279    2294     +15
ipneigh_list_or_flush                                763     772      +9
ipaddr_list_or_flush                                1256    1261      +5
display_process_list                                1301    1306      +5
conspy_main                                         1378    1383      +5
do_lzo_compress                                      352     355      +3
do_lzo_decompress                                    565     567      +2
inetd_main                                          2136    2134      -2
bb_common_bufsiz1                                   8193       -   -8193
------------------------------------------------------------------------------
(add/remove: 0/1 grow/shrink: 8/1 up/down: 62/-8195)        Total: -8133 bytes
   text	   data	    bss	    dec	    hex	filename
 829850	   4086	   9080	 843016	  cdd08	busybox_old
 829911	   4086	    880	 834877	  cbd3d	busybox_unstripped

FIXME: setup_common_bufsiz() calls are missing.

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
2016-04-21 17:39:11 +02:00

75 lines
2.6 KiB
C

/* vi: set sw=4 ts=4: */
/*
* Utility routines.
*
* Copyright (C) 2016 Denys Vlasenko
*
* Licensed under GPLv2, see file LICENSE in this source tree.
*/
//config:config FEATURE_USE_BSS_TAIL
//config: bool "Use the end of BSS page"
//config: default n
//config: help
//config: Attempt to reclaim a small unused part of BSS.
//config:
//config: Executables have the following parts:
//config: = read-only executable code and constants, also known as "text"
//config: = read-write data
//config: = non-initialized (zeroed on demand) data, also known as "bss"
//config:
//config: At link time, "text" is padded to a full page. At runtime, all "text"
//config: pages are mapped RO and executable.
//config: "Data" starts on the next page boundary, but is not padded
//config: to a full page at the end. "Bss" starts wherever "data" ends.
//config: At runtime, "data" pages are mapped RW and they are file-backed
//config: (this includes a small portion of "bss" which may live in the last
//config: partial page of "data").
//config: Pages which are fully in "bss" are mapped to anonymous memory.
//config:
//config: "Bss" end is usually not page-aligned. There is an unused space
//config: in the last page. Linker marks its start with the "_end" symbol.
//config:
//config: This option will attempt to use that space for bb_common_bufsiz1[]
//config: array. If it fits after _end, it will be used, and COMMON_BUFSIZE
//config: will be enlarged from its guaranteed minimum size of 1 kbyte.
//config: This may require recompilation a second time, since value of _end
//config: is known only after final link.
//config:
//config: If you are getting a build error like this:
//config: appletlib.c:(.text.main+0xd): undefined reference to '_end'
//config: disable this option.
//kbuild:lib-y += common_bufsiz.o
#include "libbb.h"
#include "common_bufsiz.h"
#if !ENABLE_FEATURE_USE_BSS_TAIL
/* We use it for "global" data via *(struct global*)bb_common_bufsiz1.
* Since gcc insists on aligning struct global's members, it would be a pity
* (and an alignment fault on some CPUs) to mess it up. */
char bb_common_bufsiz1[COMMON_BUFSIZE] ALIGNED(sizeof(long long));
#else
# ifndef setup_common_bufsiz
/*
* It is not a "((void)0)" macro. It means we have to provide this function.
*/
char* bb_common_bufsiz1;
char* setup_common_bufsiz(void)
{
if (!bb_common_bufsiz1)
bb_common_bufsiz1 = xzalloc(COMMON_BUFSIZE);
return bb_common_bufsiz1;
}
# else
# ifndef bb_common_bufsiz1
/* bb_common_bufsiz1[] is not aliased to _end[] */
char bb_common_bufsiz1[COMMON_BUFSIZE] ALIGNED(sizeof(long long));
# endif
# endif
#endif