| /* 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 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 |