211:, statically allocated objects without an explicit initializer are initialized to zero (for arithmetic types) or a null pointer (for pointer types). Implementations of C typically represent zero values and null pointer values using a bit pattern consisting solely of zero-valued bits (despite filling bss with zero is not required by the C standard, all variables in .bss are required to be individually initialized to some sort of zeroes according to Section 6.7.8 of C ISO Standard 9899:1999 or section 6.7.9 for newer standards). Hence, the BSS segment typically includes all uninitialized objects (both variables and
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243:, a C programmer and author, says, "Some people like to remember it as 'Better Save Space'. Since the BSS segment only holds variables that don't have any value yet, it doesn't actually need to store the image of these variables. The size that BSS will require at runtime is recorded in the object file, but BSS (unlike the data segment) doesn't take up any actual space in the object file."
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must be initialized at declaration, however, as they do not have a separate declaration, and thus are typically not in the BSS section, though they may be implicitly or explicitly initialized to zero. An implementation may also assign statically-allocated variables and constants initialized with a
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instruction sets, limit offsets, in instructions that access this segment, to 32 bits, limiting its size to 2 GB or 4 GB. Also, note that
Fortran does not require static data to be initialized to zero. On those systems where the bss segment is initialized to zero, putting common
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statically allocated variables that are initialized to all zero bits. Operating systems may use a technique called zero-fill-on-demand to efficiently implement the bss segment. In embedded software, the bss segment is mapped into memory that is initialized to zero by the C
191:. In this situation BSS served as a shorthand in place of individually reserving a number of separate smaller data locations. Some assemblers support a complementary or alternative directive
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segment for "small data". Typically, these data items can be accessed using shorter instructions that may only be able to access a certain range of addresses. Architectures supporting
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is entered. Some C run-time systems may allow part of the bss segment not to be initialized; C variables must explicitly be placed into that portion of the bss segment.
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block variables and other static data into that segment guarantees that it will be zero, but for portability, programmers should not depend on that.
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allocates memory for the bss section when it loads the program. By placing variables with no value in the .bss section, instead of the
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This shows the typical layout of a simple computer's program memory with the text, various data, and stack and heap sections.
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that are declared but have not been assigned a value yet. It is often referred to as the "bss section" or "bss segment".
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computers. It defined a label (i.e. symbol) and reserved a block of uninitialized space for a given number of
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or .rodata section which require initial value data, the size of the object file is reduced.
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IBM 7090/7094 IBSYS Operating System
Version 13 Macro Assembly Program (MAP) Language
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255:, common block variables are allocated in this segment. Some compilers may, for
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On some platforms, some or all of the bss section is initialized to zeroes.
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Typically only the length of the bss section, but no data, is stored in the
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199:, where the specified symbol corresponds to the end of the reserved block.
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Using the GNU Compiler
Collection (GCC) – GCC 7.2.0
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Using the GNU Compiler
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Using the GNU Compiler
Collection (GCC) – GCC 7.2.0
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value consisting solely of zero-valued bits to the BSS section.
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section for uninitialized, static data marked as thread-local.
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initialize the bss section to zero, which can thus be used for
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Service set (802.11 network) § Basic service sets (BSSs)
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Coding for the MIT-IBM 704 Computer
October 1957, p. V-10
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Code section for declared statically-allocated variables
313:"A New Virtual Memory Implementation for Berkeley UNIX"
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How does
Fortran 77 allocate common-block variables?
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FORTRAN ASSEMBLY PROGRAM (FAP) for the IBM 709/7090
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30:For a Basic Service Set (BSS) in a Wi-Fi LAN, see
318:. University of California, Berkeley. p. 3.
163:(United Aircraft Symbolic Assembly Program), the
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175:. The BSS keyword was later incorporated into
574:Advanced Programming in the Unix Environment
362:Linux Standard Base PDA Specification 3.0RC1
171:by Roy Nutt, Walter Ramshaw, and others at
446:"Unix - Frequently Asked Questions (1/7)"
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179:(FAP) and Macro Assembly Program (MAP),
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465:Using as: Using as, the Gnu Assembler
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491:Expert C Programming: Deep C Secrets
622:Programming language implementation
406:. IBM. 1961. p. 30. J28-6098-1
167:developed in the mid-1950s for the
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515:"IBM RS/6000 and PowerPC Options"
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444:Timar, Ted; et al. (1996).
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183:'s standard assemblers for its
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63:statically allocated variables
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493:, Prentice Hall 1994, p. 141
377:. Javvin Press, 2007, p. 70.
117:application binary interface
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173:United Aircraft Corporation
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433:. IBM. 1963. C28-6392-4.
177:FORTRAN Assembly Program
607:Executable file formats
305:McKusick, Marshall Kirk
153:Block Started by Symbol
53:) is the portion of an
489:Peter van der Linden,
358:"ELF Special Sections"
285:Uninitialized variable
217:static local variables
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113:computer architectures
197:Block Ended by Symbol
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43:block starting symbol
280:Code segment (.text)
275:Data segment (.data)
241:Peter van der Linden
125:thread-local storage
39:computer programming
568:Stevens, W. Richard
61:code that contains
617:Assembly languages
461:"38.9. Directives"
375:Network Dictionary
344:AVR Libc Home page
309:Karels, Michael J.
270:Linker (computing)
223:declared with the
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612:Memory management
471:on March 19, 2014
340:"Memory Sections"
119:also supports an
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57:, executable, or
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582:. Section 7.6.
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448:. Question 1.3.
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18:BSS segment
601:Categories
410:18 October
291:References
320:CiteSeerX
234:constants
213:constants
165:assembler
85:Unix-like
570:(1992).
311:(1986).
264:See also
203:BSS in C
111:On some
475:Feb 22,
253:Fortran
230:keyword
169:IBM 704
155:) is a
104:before
89:Windows
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257:64-bit
226:static
195:, for
161:UA-SAP
151:(from
135:Origin
115:, the
106:main()
72:. The
41:, the
431:(PDF)
404:(PDF)
316:(PDF)
189:words
78:.data
584:ISBN
477:2014
412:2017
129:tbss
121:sbss
95:and
47:.bss
251:In
207:In
193:BES
181:IBM
159:in
149:BSS
97:C++
51:bss
49:or
37:In
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