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/* 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
/* For now, this is never used:
* scripts/generate_BUFSIZ.sh never generates "malloced" bufsiz1:
* enum { COMMON_BUFSIZE = 1024 };
* extern char *const bb_common_bufsiz1;
* void setup_common_bufsiz(void);
* This has proved to be worse than the approach of defining
* larger bb_common_bufsiz1[] array.
*/
/*
* It is not defined as a dummy macro.
* It means we have to provide this function.
*/
char *const bb_common_bufsiz1 __attribute__ ((section (".data")));
void setup_common_bufsiz(void)
{
if (!bb_common_bufsiz1)
*(char**)&bb_common_bufsiz1 = xzalloc(COMMON_BUFSIZE);
}
# 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
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