650 lines
22 KiB
Plaintext
650 lines
22 KiB
Plaintext
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@section Sections
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The raw data contained within a BFD is maintained through the
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section abstraction. A single BFD may have any number of
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sections. It keeps hold of them by pointing to the first;
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each one points to the next in the list.
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Sections are supported in BFD in @code{section.c}.
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@menu
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* Section Input::
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* Section Output::
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* typedef asection::
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* section prototypes::
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@end menu
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@*
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@node Section Input, Section Output, Sections, Sections
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@subsection Section input
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When a BFD is opened for reading, the section structures are
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created and attached to the BFD.
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Each section has a name which describes the section in the
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outside world---for example, @code{a.out} would contain at least
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three sections, called @code{.text}, @code{.data} and @code{.bss}.
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Names need not be unique; for example a COFF file may have several
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sections named @code{.data}.
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Sometimes a BFD will contain more than the ``natural'' number of
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sections. A back end may attach other sections containing
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constructor data, or an application may add a section (using
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@code{bfd_make_section}) to the sections attached to an already open
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BFD. For example, the linker creates an extra section
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@code{COMMON} for each input file's BFD to hold information about
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common storage.
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The raw data is not necessarily read in when
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the section descriptor is created. Some targets may leave the
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data in place until a @code{bfd_get_section_contents} call is
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made. Other back ends may read in all the data at once. For
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example, an S-record file has to be read once to determine the
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size of the data. An IEEE-695 file doesn't contain raw data in
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sections, but data and relocation expressions intermixed, so
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the data area has to be parsed to get out the data and
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relocations.
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@*
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@node Section Output, typedef asection, Section Input, Sections
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@subsection Section output
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To write a new object style BFD, the various sections to be
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written have to be created. They are attached to the BFD in
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the same way as input sections; data is written to the
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sections using @code{bfd_set_section_contents}.
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Any program that creates or combines sections (e.g., the assembler
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and linker) must use the @code{asection} fields @code{output_section} and
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@code{output_offset} to indicate the file sections to which each
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section must be written. (If the section is being created from
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scratch, @code{output_section} should probably point to the section
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itself and @code{output_offset} should probably be zero.)
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The data to be written comes from input sections attached
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(via @code{output_section} pointers) to
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the output sections. The output section structure can be
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considered a filter for the input section: the output section
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determines the vma of the output data and the name, but the
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input section determines the offset into the output section of
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the data to be written.
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E.g., to create a section "O", starting at 0x100, 0x123 long,
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containing two subsections, "A" at offset 0x0 (i.e., at vma
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0x100) and "B" at offset 0x20 (i.e., at vma 0x120) the @code{asection}
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structures would look like:
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@example
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section name "A"
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output_offset 0x00
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size 0x20
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output_section -----------> section name "O"
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| vma 0x100
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section name "B" | size 0x123
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output_offset 0x20 |
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size 0x103 |
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output_section --------|
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@end example
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@*
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@subsection Link orders
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The data within a section is stored in a @dfn{link_order}.
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These are much like the fixups in @code{gas}. The link_order
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abstraction allows a section to grow and shrink within itself.
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A link_order knows how big it is, and which is the next
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link_order and where the raw data for it is; it also points to
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a list of relocations which apply to it.
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The link_order is used by the linker to perform relaxing on
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final code. The compiler creates code which is as big as
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necessary to make it work without relaxing, and the user can
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select whether to relax. Sometimes relaxing takes a lot of
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time. The linker runs around the relocations to see if any
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are attached to data which can be shrunk, if so it does it on
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a link_order by link_order basis.
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@*
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@node typedef asection, section prototypes, Section Output, Sections
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@subsection typedef asection
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Here is the section structure:
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@*
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.
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@example
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typedef struct sec
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@{
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/* The name of the section; the name isn't a copy, the pointer is
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the same as that passed to bfd_make_section. */
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CONST char *name;
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/* Which section is it; 0..nth. */
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int index;
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/* The next section in the list belonging to the BFD, or NULL. */
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struct sec *next;
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/* The field flags contains attributes of the section. Some
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flags are read in from the object file, and some are
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synthesized from other information. */
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flagword flags;
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#define SEC_NO_FLAGS 0x000
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/* Tells the OS to allocate space for this section when loading.
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This is clear for a section containing debug information
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only. */
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#define SEC_ALLOC 0x001
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/* Tells the OS to load the section from the file when loading.
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This is clear for a .bss section. */
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#define SEC_LOAD 0x002
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/* The section contains data still to be relocated, so there is
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some relocation information too. */
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#define SEC_RELOC 0x004
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#if 0 /* Obsolete ? */
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#define SEC_BALIGN 0x008
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#endif
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/* A signal to the OS that the section contains read only
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data. */
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#define SEC_READONLY 0x010
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/* The section contains code only. */
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#define SEC_CODE 0x020
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/* The section contains data only. */
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#define SEC_DATA 0x040
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/* The section will reside in ROM. */
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#define SEC_ROM 0x080
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/* The section contains constructor information. This section
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type is used by the linker to create lists of constructors and
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destructors used by @code{g++}. When a back end sees a symbol
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which should be used in a constructor list, it creates a new
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section for the type of name (e.g., @code{__CTOR_LIST__}), attaches
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the symbol to it, and builds a relocation. To build the lists
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of constructors, all the linker has to do is catenate all the
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sections called @code{__CTOR_LIST__} and relocate the data
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contained within - exactly the operations it would peform on
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standard data. */
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#define SEC_CONSTRUCTOR 0x100
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/* The section is a constuctor, and should be placed at the
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end of the text, data, or bss section(?). */
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#define SEC_CONSTRUCTOR_TEXT 0x1100
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#define SEC_CONSTRUCTOR_DATA 0x2100
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#define SEC_CONSTRUCTOR_BSS 0x3100
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/* The section has contents - a data section could be
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@code{SEC_ALLOC} | @code{SEC_HAS_CONTENTS}; a debug section could be
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@code{SEC_HAS_CONTENTS} */
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#define SEC_HAS_CONTENTS 0x200
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/* An instruction to the linker to not output the section
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even if it has information which would normally be written. */
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#define SEC_NEVER_LOAD 0x400
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/* The section is a COFF shared library section. This flag is
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only for the linker. If this type of section appears in
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the input file, the linker must copy it to the output file
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without changing the vma or size. FIXME: Although this
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was originally intended to be general, it really is COFF
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specific (and the flag was renamed to indicate this). It
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might be cleaner to have some more general mechanism to
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allow the back end to control what the linker does with
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sections. */
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#define SEC_COFF_SHARED_LIBRARY 0x800
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/* The section contains common symbols (symbols may be defined
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multiple times, the value of a symbol is the amount of
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space it requires, and the largest symbol value is the one
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used). Most targets have exactly one of these (which we
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translate to bfd_com_section_ptr), but ECOFF has two. */
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#define SEC_IS_COMMON 0x8000
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/* The section contains only debugging information. For
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example, this is set for ELF .debug and .stab sections.
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strip tests this flag to see if a section can be
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discarded. */
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#define SEC_DEBUGGING 0x10000
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/* The contents of this section are held in memory pointed to
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by the contents field. This is checked by
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bfd_get_section_contents, and the data is retrieved from
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memory if appropriate. */
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#define SEC_IN_MEMORY 0x20000
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/* The contents of this section are to be excluded by the
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linker for executable and shared objects unless those
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objects are to be further relocated. */
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#define SEC_EXCLUDE 0x40000
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/* The contents of this section are to be sorted by the
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based on the address specified in the associated symbol
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table. */
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#define SEC_SORT_ENTRIES 0x80000
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/* When linking, duplicate sections of the same name should be
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discarded, rather than being combined into a single section as
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is usually done. This is similar to how common symbols are
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handled. See SEC_LINK_DUPLICATES below. */
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#define SEC_LINK_ONCE 0x100000
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/* If SEC_LINK_ONCE is set, this bitfield describes how the linker
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should handle duplicate sections. */
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#define SEC_LINK_DUPLICATES 0x600000
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/* This value for SEC_LINK_DUPLICATES means that duplicate
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sections with the same name should simply be discarded. */
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#define SEC_LINK_DUPLICATES_DISCARD 0x0
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/* This value for SEC_LINK_DUPLICATES means that the linker
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should warn if there are any duplicate sections, although
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it should still only link one copy. */
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#define SEC_LINK_DUPLICATES_ONE_ONLY 0x200000
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/* This value for SEC_LINK_DUPLICATES means that the linker
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should warn if any duplicate sections are a different size. */
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#define SEC_LINK_DUPLICATES_SAME_SIZE 0x400000
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/* This value for SEC_LINK_DUPLICATES means that the linker
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should warn if any duplicate sections contain different
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contents. */
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#define SEC_LINK_DUPLICATES_SAME_CONTENTS 0x600000
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/* This section was created by the linker as part of dynamic
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relocation or other arcane processing. It is skipped when
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going through the first-pass output, trusting that someone
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else up the line will take care of it later. */
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#define SEC_LINKER_CREATED 0x800000
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/* End of section flags. */
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/* Some internal packed boolean fields. */
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/* See the vma field. */
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unsigned int user_set_vma : 1;
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/* Whether relocations have been processed. */
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unsigned int reloc_done : 1;
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/* A mark flag used by some of the linker backends. */
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unsigned int linker_mark : 1;
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/* End of internal packed boolean fields. */
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/* The virtual memory address of the section - where it will be
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at run time. The symbols are relocated against this. The
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user_set_vma flag is maintained by bfd; if it's not set, the
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backend can assign addresses (for example, in @code{a.out}, where
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the default address for @code{.data} is dependent on the specific
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target and various flags). */
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bfd_vma vma;
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/* The load address of the section - where it would be in a
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rom image; really only used for writing section header
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information. */
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bfd_vma lma;
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/* The size of the section in bytes, as it will be output.
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contains a value even if the section has no contents (e.g., the
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size of @code{.bss}). This will be filled in after relocation */
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bfd_size_type _cooked_size;
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/* The original size on disk of the section, in bytes. Normally this
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value is the same as the size, but if some relaxing has
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been done, then this value will be bigger. */
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bfd_size_type _raw_size;
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/* If this section is going to be output, then this value is the
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offset into the output section of the first byte in the input
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section. E.g., if this was going to start at the 100th byte in
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the output section, this value would be 100. */
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bfd_vma output_offset;
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/* The output section through which to map on output. */
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struct sec *output_section;
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/* The alignment requirement of the section, as an exponent of 2 -
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e.g., 3 aligns to 2^3 (or 8). */
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unsigned int alignment_power;
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/* If an input section, a pointer to a vector of relocation
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records for the data in this section. */
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struct reloc_cache_entry *relocation;
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/* If an output section, a pointer to a vector of pointers to
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relocation records for the data in this section. */
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struct reloc_cache_entry **orelocation;
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/* The number of relocation records in one of the above */
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unsigned reloc_count;
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/* Information below is back end specific - and not always used
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or updated. */
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/* File position of section data */
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file_ptr filepos;
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/* File position of relocation info */
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file_ptr rel_filepos;
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/* File position of line data */
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file_ptr line_filepos;
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/* Pointer to data for applications */
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PTR userdata;
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/* If the SEC_IN_MEMORY flag is set, this points to the actual
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contents. */
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unsigned char *contents;
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/* Attached line number information */
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alent *lineno;
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/* Number of line number records */
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unsigned int lineno_count;
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/* When a section is being output, this value changes as more
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linenumbers are written out */
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file_ptr moving_line_filepos;
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/* What the section number is in the target world */
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int target_index;
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PTR used_by_bfd;
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/* If this is a constructor section then here is a list of the
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relocations created to relocate items within it. */
|
||
|
|
|
||
|
|
struct relent_chain *constructor_chain;
|
||
|
|
|
||
|
|
/* The BFD which owns the section. */
|
||
|
|
|
||
|
|
bfd *owner;
|
||
|
|
|
||
|
|
/* A symbol which points at this section only */
|
||
|
|
struct symbol_cache_entry *symbol;
|
||
|
|
struct symbol_cache_entry **symbol_ptr_ptr;
|
||
|
|
|
||
|
|
struct bfd_link_order *link_order_head;
|
||
|
|
struct bfd_link_order *link_order_tail;
|
||
|
|
@} asection ;
|
||
|
|
|
||
|
|
/* These sections are global, and are managed by BFD. The application
|
||
|
|
and target back end are not permitted to change the values in
|
||
|
|
these sections. New code should use the section_ptr macros rather
|
||
|
|
than referring directly to the const sections. The const sections
|
||
|
|
may eventually vanish. */
|
||
|
|
#define BFD_ABS_SECTION_NAME "*ABS*"
|
||
|
|
#define BFD_UND_SECTION_NAME "*UND*"
|
||
|
|
#define BFD_COM_SECTION_NAME "*COM*"
|
||
|
|
#define BFD_IND_SECTION_NAME "*IND*"
|
||
|
|
|
||
|
|
/* the absolute section */
|
||
|
|
extern const asection bfd_abs_section;
|
||
|
|
#define bfd_abs_section_ptr ((asection *) &bfd_abs_section)
|
||
|
|
#define bfd_is_abs_section(sec) ((sec) == bfd_abs_section_ptr)
|
||
|
|
/* Pointer to the undefined section */
|
||
|
|
extern const asection bfd_und_section;
|
||
|
|
#define bfd_und_section_ptr ((asection *) &bfd_und_section)
|
||
|
|
#define bfd_is_und_section(sec) ((sec) == bfd_und_section_ptr)
|
||
|
|
/* Pointer to the common section */
|
||
|
|
extern const asection bfd_com_section;
|
||
|
|
#define bfd_com_section_ptr ((asection *) &bfd_com_section)
|
||
|
|
/* Pointer to the indirect section */
|
||
|
|
extern const asection bfd_ind_section;
|
||
|
|
#define bfd_ind_section_ptr ((asection *) &bfd_ind_section)
|
||
|
|
#define bfd_is_ind_section(sec) ((sec) == bfd_ind_section_ptr)
|
||
|
|
|
||
|
|
extern const struct symbol_cache_entry * const bfd_abs_symbol;
|
||
|
|
extern const struct symbol_cache_entry * const bfd_com_symbol;
|
||
|
|
extern const struct symbol_cache_entry * const bfd_und_symbol;
|
||
|
|
extern const struct symbol_cache_entry * const bfd_ind_symbol;
|
||
|
|
#define bfd_get_section_size_before_reloc(section) \
|
||
|
|
(section->reloc_done ? (abort(),1): (section)->_raw_size)
|
||
|
|
#define bfd_get_section_size_after_reloc(section) \
|
||
|
|
((section->reloc_done) ? (section)->_cooked_size: (abort(),1))
|
||
|
|
@end example
|
||
|
|
|
||
|
|
@node section prototypes, , typedef asection, Sections
|
||
|
|
@subsection Section prototypes
|
||
|
|
These are the functions exported by the section handling part of BFD.
|
||
|
|
@*
|
||
|
|
@findex bfd_get_section_by_name
|
||
|
|
@subsubsection @code{bfd_get_section_by_name}
|
||
|
|
@strong{Synopsis}
|
||
|
|
@example
|
||
|
|
asection *bfd_get_section_by_name(bfd *abfd, CONST char *name);
|
||
|
|
@end example
|
||
|
|
@strong{Description}@*
|
||
|
|
Run through @var{abfd} and return the one of the
|
||
|
|
@code{asection}s whose name matches @var{name}, otherwise @code{NULL}.
|
||
|
|
@xref{Sections}, for more information.
|
||
|
|
|
||
|
|
This should only be used in special cases; the normal way to process
|
||
|
|
all sections of a given name is to use @code{bfd_map_over_sections} and
|
||
|
|
@code{strcmp} on the name (or better yet, base it on the section flags
|
||
|
|
or something else) for each section.
|
||
|
|
@*
|
||
|
|
@findex bfd_make_section_old_way
|
||
|
|
@subsubsection @code{bfd_make_section_old_way}
|
||
|
|
@strong{Synopsis}
|
||
|
|
@example
|
||
|
|
asection *bfd_make_section_old_way(bfd *abfd, CONST char *name);
|
||
|
|
@end example
|
||
|
|
@strong{Description}@*
|
||
|
|
Create a new empty section called @var{name}
|
||
|
|
and attach it to the end of the chain of sections for the
|
||
|
|
BFD @var{abfd}. An attempt to create a section with a name which
|
||
|
|
is already in use returns its pointer without changing the
|
||
|
|
section chain.
|
||
|
|
|
||
|
|
It has the funny name since this is the way it used to be
|
||
|
|
before it was rewritten....
|
||
|
|
|
||
|
|
Possible errors are:
|
||
|
|
@itemize @bullet
|
||
|
|
|
||
|
|
@item
|
||
|
|
@code{bfd_error_invalid_operation} -
|
||
|
|
If output has already started for this BFD.
|
||
|
|
@item
|
||
|
|
@code{bfd_error_no_memory} -
|
||
|
|
If memory allocation fails.
|
||
|
|
@end itemize
|
||
|
|
@*
|
||
|
|
@findex bfd_make_section_anyway
|
||
|
|
@subsubsection @code{bfd_make_section_anyway}
|
||
|
|
@strong{Synopsis}
|
||
|
|
@example
|
||
|
|
asection *bfd_make_section_anyway(bfd *abfd, CONST char *name);
|
||
|
|
@end example
|
||
|
|
@strong{Description}@*
|
||
|
|
Create a new empty section called @var{name} and attach it to the end of
|
||
|
|
the chain of sections for @var{abfd}. Create a new section even if there
|
||
|
|
is already a section with that name.
|
||
|
|
|
||
|
|
Return @code{NULL} and set @code{bfd_error} on error; possible errors are:
|
||
|
|
@itemize @bullet
|
||
|
|
|
||
|
|
@item
|
||
|
|
@code{bfd_error_invalid_operation} - If output has already started for @var{abfd}.
|
||
|
|
@item
|
||
|
|
@code{bfd_error_no_memory} - If memory allocation fails.
|
||
|
|
@end itemize
|
||
|
|
@*
|
||
|
|
@findex bfd_make_section
|
||
|
|
@subsubsection @code{bfd_make_section}
|
||
|
|
@strong{Synopsis}
|
||
|
|
@example
|
||
|
|
asection *bfd_make_section(bfd *, CONST char *name);
|
||
|
|
@end example
|
||
|
|
@strong{Description}@*
|
||
|
|
Like @code{bfd_make_section_anyway}, but return @code{NULL} (without calling
|
||
|
|
bfd_set_error ()) without changing the section chain if there is already a
|
||
|
|
section named @var{name}. If there is an error, return @code{NULL} and set
|
||
|
|
@code{bfd_error}.
|
||
|
|
@*
|
||
|
|
@findex bfd_set_section_flags
|
||
|
|
@subsubsection @code{bfd_set_section_flags}
|
||
|
|
@strong{Synopsis}
|
||
|
|
@example
|
||
|
|
boolean bfd_set_section_flags(bfd *abfd, asection *sec, flagword flags);
|
||
|
|
@end example
|
||
|
|
@strong{Description}@*
|
||
|
|
Set the attributes of the section @var{sec} in the BFD
|
||
|
|
@var{abfd} to the value @var{flags}. Return @code{true} on success,
|
||
|
|
@code{false} on error. Possible error returns are:
|
||
|
|
|
||
|
|
@itemize @bullet
|
||
|
|
|
||
|
|
@item
|
||
|
|
@code{bfd_error_invalid_operation} -
|
||
|
|
The section cannot have one or more of the attributes
|
||
|
|
requested. For example, a .bss section in @code{a.out} may not
|
||
|
|
have the @code{SEC_HAS_CONTENTS} field set.
|
||
|
|
@end itemize
|
||
|
|
@*
|
||
|
|
@findex bfd_map_over_sections
|
||
|
|
@subsubsection @code{bfd_map_over_sections}
|
||
|
|
@strong{Synopsis}
|
||
|
|
@example
|
||
|
|
void bfd_map_over_sections(bfd *abfd,
|
||
|
|
void (*func)(bfd *abfd,
|
||
|
|
asection *sect,
|
||
|
|
PTR obj),
|
||
|
|
PTR obj);
|
||
|
|
@end example
|
||
|
|
@strong{Description}@*
|
||
|
|
Call the provided function @var{func} for each section
|
||
|
|
attached to the BFD @var{abfd}, passing @var{obj} as an
|
||
|
|
argument. The function will be called as if by
|
||
|
|
|
||
|
|
@example
|
||
|
|
func(abfd, the_section, obj);
|
||
|
|
@end example
|
||
|
|
|
||
|
|
This is the prefered method for iterating over sections; an
|
||
|
|
alternative would be to use a loop:
|
||
|
|
|
||
|
|
@example
|
||
|
|
section *p;
|
||
|
|
for (p = abfd->sections; p != NULL; p = p->next)
|
||
|
|
func(abfd, p, ...)
|
||
|
|
@end example
|
||
|
|
@*
|
||
|
|
@findex bfd_set_section_size
|
||
|
|
@subsubsection @code{bfd_set_section_size}
|
||
|
|
@strong{Synopsis}
|
||
|
|
@example
|
||
|
|
boolean bfd_set_section_size(bfd *abfd, asection *sec, bfd_size_type val);
|
||
|
|
@end example
|
||
|
|
@strong{Description}@*
|
||
|
|
Set @var{sec} to the size @var{val}. If the operation is
|
||
|
|
ok, then @code{true} is returned, else @code{false}.
|
||
|
|
|
||
|
|
Possible error returns:
|
||
|
|
@itemize @bullet
|
||
|
|
|
||
|
|
@item
|
||
|
|
@code{bfd_error_invalid_operation} -
|
||
|
|
Writing has started to the BFD, so setting the size is invalid.
|
||
|
|
@end itemize
|
||
|
|
@*
|
||
|
|
@findex bfd_set_section_contents
|
||
|
|
@subsubsection @code{bfd_set_section_contents}
|
||
|
|
@strong{Synopsis}
|
||
|
|
@example
|
||
|
|
boolean bfd_set_section_contents
|
||
|
|
(bfd *abfd,
|
||
|
|
asection *section,
|
||
|
|
PTR data,
|
||
|
|
file_ptr offset,
|
||
|
|
bfd_size_type count);
|
||
|
|
@end example
|
||
|
|
@strong{Description}@*
|
||
|
|
Sets the contents of the section @var{section} in BFD
|
||
|
|
@var{abfd} to the data starting in memory at @var{data}. The
|
||
|
|
data is written to the output section starting at offset
|
||
|
|
@var{offset} for @var{count} bytes.
|
||
|
|
|
||
|
|
Normally @code{true} is returned, else @code{false}. Possible error
|
||
|
|
returns are:
|
||
|
|
@itemize @bullet
|
||
|
|
|
||
|
|
@item
|
||
|
|
@code{bfd_error_no_contents} -
|
||
|
|
The output section does not have the @code{SEC_HAS_CONTENTS}
|
||
|
|
attribute, so nothing can be written to it.
|
||
|
|
@item
|
||
|
|
and some more too
|
||
|
|
@end itemize
|
||
|
|
This routine is front end to the back end function
|
||
|
|
@code{_bfd_set_section_contents}.
|
||
|
|
@*
|
||
|
|
@findex bfd_get_section_contents
|
||
|
|
@subsubsection @code{bfd_get_section_contents}
|
||
|
|
@strong{Synopsis}
|
||
|
|
@example
|
||
|
|
boolean bfd_get_section_contents
|
||
|
|
(bfd *abfd, asection *section, PTR location,
|
||
|
|
file_ptr offset, bfd_size_type count);
|
||
|
|
@end example
|
||
|
|
@strong{Description}@*
|
||
|
|
Read data from @var{section} in BFD @var{abfd}
|
||
|
|
into memory starting at @var{location}. The data is read at an
|
||
|
|
offset of @var{offset} from the start of the input section,
|
||
|
|
and is read for @var{count} bytes.
|
||
|
|
|
||
|
|
If the contents of a constructor with the @code{SEC_CONSTRUCTOR}
|
||
|
|
flag set are requested or if the section does not have the
|
||
|
|
@code{SEC_HAS_CONTENTS} flag set, then the @var{location} is filled
|
||
|
|
with zeroes. If no errors occur, @code{true} is returned, else
|
||
|
|
@code{false}.
|
||
|
|
@*
|
||
|
|
@findex bfd_copy_private_section_data
|
||
|
|
@subsubsection @code{bfd_copy_private_section_data}
|
||
|
|
@strong{Synopsis}
|
||
|
|
@example
|
||
|
|
boolean bfd_copy_private_section_data(bfd *ibfd, asection *isec, bfd *obfd, asection *osec);
|
||
|
|
@end example
|
||
|
|
@strong{Description}@*
|
||
|
|
Copy private section information from @var{isec} in the BFD
|
||
|
|
@var{ibfd} to the section @var{osec} in the BFD @var{obfd}.
|
||
|
|
Return @code{true} on success, @code{false} on error. Possible error
|
||
|
|
returns are:
|
||
|
|
|
||
|
|
@itemize @bullet
|
||
|
|
|
||
|
|
@item
|
||
|
|
@code{bfd_error_no_memory} -
|
||
|
|
Not enough memory exists to create private data for @var{osec}.
|
||
|
|
@end itemize
|
||
|
|
@example
|
||
|
|
#define bfd_copy_private_section_data(ibfd, isection, obfd, osection) \
|
||
|
|
BFD_SEND (obfd, _bfd_copy_private_section_data, \
|
||
|
|
(ibfd, isection, obfd, osection))
|
||
|
|
@end example
|
||
|
|
@*
|