[3621] | 1 | /* vi: set sw=4 ts=4: */
|
---|
| 2 | /*
|
---|
| 3 | * Utility routines.
|
---|
| 4 | *
|
---|
| 5 | * Copyright (C) 2016 Denys Vlasenko
|
---|
| 6 | *
|
---|
| 7 | * Licensed under GPLv2, see file LICENSE in this source tree.
|
---|
| 8 | */
|
---|
| 9 | //config:config FEATURE_USE_BSS_TAIL
|
---|
| 10 | //config: bool "Use the end of BSS page"
|
---|
| 11 | //config: default n
|
---|
| 12 | //config: help
|
---|
| 13 | //config: Attempt to reclaim a small unused part of BSS.
|
---|
| 14 | //config:
|
---|
| 15 | //config: Executables have the following parts:
|
---|
| 16 | //config: = read-only executable code and constants, also known as "text"
|
---|
| 17 | //config: = read-write data
|
---|
| 18 | //config: = non-initialized (zeroed on demand) data, also known as "bss"
|
---|
| 19 | //config:
|
---|
| 20 | //config: At link time, "text" is padded to a full page. At runtime, all "text"
|
---|
| 21 | //config: pages are mapped RO and executable.
|
---|
| 22 | //config: "Data" starts on the next page boundary, but is not padded
|
---|
| 23 | //config: to a full page at the end. "Bss" starts wherever "data" ends.
|
---|
| 24 | //config: At runtime, "data" pages are mapped RW and they are file-backed
|
---|
| 25 | //config: (this includes a small portion of "bss" which may live in the last
|
---|
| 26 | //config: partial page of "data").
|
---|
| 27 | //config: Pages which are fully in "bss" are mapped to anonymous memory.
|
---|
| 28 | //config:
|
---|
| 29 | //config: "Bss" end is usually not page-aligned. There is an unused space
|
---|
| 30 | //config: in the last page. Linker marks its start with the "_end" symbol.
|
---|
| 31 | //config:
|
---|
| 32 | //config: This option will attempt to use that space for bb_common_bufsiz1[]
|
---|
| 33 | //config: array. If it fits after _end, it will be used, and COMMON_BUFSIZE
|
---|
| 34 | //config: will be enlarged from its guaranteed minimum size of 1 kbyte.
|
---|
| 35 | //config: This may require recompilation a second time, since value of _end
|
---|
| 36 | //config: is known only after final link.
|
---|
| 37 | //config:
|
---|
| 38 | //config: If you are getting a build error like this:
|
---|
| 39 | //config: appletlib.c:(.text.main+0xd): undefined reference to '_end'
|
---|
| 40 | //config: disable this option.
|
---|
| 41 |
|
---|
| 42 | //kbuild:lib-y += common_bufsiz.o
|
---|
| 43 |
|
---|
| 44 | #include "libbb.h"
|
---|
| 45 | #include "common_bufsiz.h"
|
---|
| 46 |
|
---|
| 47 | #if !ENABLE_FEATURE_USE_BSS_TAIL
|
---|
| 48 |
|
---|
| 49 | /* We use it for "global" data via *(struct global*)bb_common_bufsiz1.
|
---|
| 50 | * Since gcc insists on aligning struct global's members, it would be a pity
|
---|
| 51 | * (and an alignment fault on some CPUs) to mess it up. */
|
---|
| 52 | char bb_common_bufsiz1[COMMON_BUFSIZE] ALIGNED(sizeof(long long));
|
---|
| 53 |
|
---|
| 54 | #else
|
---|
| 55 |
|
---|
| 56 | # ifndef setup_common_bufsiz
|
---|
| 57 | /*
|
---|
| 58 | * It is not defined as a dummy macro.
|
---|
| 59 | * It means we have to provide this function.
|
---|
| 60 | */
|
---|
| 61 | char *const bb_common_bufsiz1 __attribute__ ((section (".data")));
|
---|
| 62 | void setup_common_bufsiz(void)
|
---|
| 63 | {
|
---|
| 64 | if (!bb_common_bufsiz1)
|
---|
| 65 | *(char**)&bb_common_bufsiz1 = xzalloc(COMMON_BUFSIZE);
|
---|
| 66 | }
|
---|
| 67 | # else
|
---|
| 68 | # ifndef bb_common_bufsiz1
|
---|
| 69 | /* bb_common_bufsiz1[] is not aliased to _end[] */
|
---|
| 70 | char bb_common_bufsiz1[COMMON_BUFSIZE] ALIGNED(sizeof(long long));
|
---|
| 71 | # endif
|
---|
| 72 | # endif
|
---|
| 73 |
|
---|
| 74 | #endif
|
---|