An object file is divided into sections containing different types of data. In the most common case, there are three sections: the text section, which holds instructions and read-only data; the data section, which holds initialized writable data; and the bss section, which holds uninitialized data. Some systems have other kinds of sections.
The compiler must tell the assembler when to switch sections. These macros control what commands to output to tell the assembler this. You can also define additional sections.
A C expression whose value is a string, including spacing, containing the assembler operation that should precede instructions and read-only data. Normally
If defined, a C string constant for the name of the section containing most frequently executed functions of the program. If not defined, GCC will provide a default definition if the target supports named sections.
If defined, a C string constant for the name of the section containing unlikely executed functions in the program.
A C expression whose value is a string, including spacing, containing the assembler operation to identify the following data as writable initialized data. Normally
A C expression whose value is a string, including spacing, containing the assembler operation to identify the following data as read-only initialized data.
A macro naming a function to call to switch to the proper section for read-only data. The default is to use
READONLY_DATA_SECTION_ASM_OPif defined, else fall back to
The most common definition will be
data_section, if the target does not have a special read-only data section, and does not put data in the text section.
If defined, a C expression whose value is a string, including spacing, containing the assembler operation to identify the following data as shared data. If not defined,
DATA_SECTION_ASM_OPwill be used.
If defined, a C expression whose value is a string, including spacing, containing the assembler operation to identify the following data as uninitialized global data. If not defined, and neither
ASM_OUTPUT_ALIGNED_BSSare defined, uninitialized global data will be output in the data section if -fno-common is passed, otherwise
ASM_OUTPUT_COMMONwill be used.
If defined, a C expression whose value is a string, including spacing, containing the assembler operation to identify the following data as initialization code. If not defined, GCC will assume such a section does not exist.
If defined, a C expression whose value is a string, including spacing, containing the assembler operation to identify the following data as finalization code. If not defined, GCC will assume such a section does not exist.
If defined, an ASM statement that switches to a different section via section_op, calls function, and switches back to the text section. This is used in crtstuff.c if
FINI_SECTION_ASM_OPto calls to initialization and finalization functions from the init and fini sections. By default, this macro uses a simple function call. Some ports need hand-crafted assembly code to avoid dependencies on registers initialized in the function prologue or to ensure that constant pools don't end up too far way in the text section.
If defined, an ASM statement that aligns a code section to some arbitrary boundary. This is used to force all fragments of the
.finisections to have to same alignment and thus prevent the linker from having to add any padding.
A list of names for sections other than the standard two, which are
in_data. You need not define this macro on a system with no other sections (that GCC needs to use).
One or more functions to be defined in varasm.c. These functions should do jobs analogous to those of
data_section, for your additional sections. Do not define this macro if you do not define
Define this macro to be an expression with a nonzero value if jump tables (for
tablejumpinsns) should be output in the text section, along with the assembler instructions. Otherwise, the readonly data section is used.
This macro is irrelevant if there is no separate readonly data section.
Switches to the appropriate section for output of exp. You can assume that exp is either a
VAR_DECLnode or a constant of some sort. reloc indicates whether the initial value of exp requires link-time relocations. Bit 0 is set when variable contains local relocations only, while bit 1 is set for global relocations. Select the section by calling
data_sectionor one of the alternatives for other sections. align is the constant alignment in bits.
The default version of this function takes care of putting read-only variables in
Build up a unique section name, expressed as a
STRING_CSTnode, and assign it to `DECL_SECTION_NAME (decl)'. As with
TARGET_ASM_SELECT_SECTION, reloc indicates whether the initial value of exp requires link-time relocations.
The default version of this function appends the symbol name to the ELF section name that would normally be used for the symbol. For example, the function
foowould be placed in
.text.foo. Whatever the actual target object format, this is often good enough.
Switches to the appropriate section for output of constant pool entry x in mode. You can assume that x is some kind of constant in RTL. The argument mode is redundant except in the case of a
const_intrtx. Select the section by calling
readonly_data_sectionor one of the alternatives for other sections. align is the constant alignment in bits.
The default version of this function takes care of putting symbolic constants in
data_sectionand everything else in
Define this hook if references to a symbol or a constant must be treated differently depending on something about the variable or function named by the symbol (such as what section it is in).
The hook is executed immediately after rtl has been created for decl, which may be a variable or function declaration or an entry in the constant pool. In either case, rtl is the rtl in question. Do not use
)in this hook; that field may not have been initialized yet.
In the case of a constant, it is safe to assume that the rtl is a
memwhose address is a
symbol_ref. Most decls will also have this form, but that is not guaranteed. Global register variables, for instance, will have a
regfor their rtl. (Normally the right thing to do with such unusual rtl is leave it alone.)
The new_decl_p argument will be true if this is the first time that
TARGET_ENCODE_SECTION_INFOhas been invoked on this decl. It will be false for subsequent invocations, which will happen for duplicate declarations. Whether or not anything must be done for the duplicate declaration depends on whether the hook examines
DECL_ATTRIBUTES. new_decl_p is always true when the hook is called for a constant.
The usual thing for this hook to do is to record flags in the
SYMBOL_REF_FLAGS. Historically, the name string was modified if it was necessary to encode more than one bit of information, but this practice is now discouraged; use
The default definition of this hook,
default_encode_section_infoin varasm.c, sets a number of commonly-useful bits in
SYMBOL_REF_FLAGS. Check whether the default does what you need before overriding it.
Decode name and return the real name part, sans the characters that
TARGET_ENCODE_SECTION_INFOmay have added.
Returns true if exp should be placed into a “small data” section. The default version of this hook always returns false.
Contains the value true if the target places read-only “small data” into a separate section. The default value is false.
Returns true if exp names an object for which name resolution rules must resolve to the current “module” (dynamic shared library or executable image).
The default version of this hook implements the name resolution rules for ELF, which has a looser model of global name binding than other currently supported object file formats.