Windows PowerShell command on Get-command elf

Manual Pages for UNIX Operating System command usage for man elf_getdata

ELF Library Functions elf_getdata(3ELF)

NAME

elf_getdata, elf_newdata, elf_rawdata - get section data

SYNOPSIS

cc [ flag ... ] file ... -lelf [ library ... ]

#include

Elf_Data elf_getdata(Elf_Scn scn, Elf_Data *data);

Elf_Data *elf_newdata(Elf_Scn *scn);

Elf_Data *elf_rawdata(Elf_Scn *scn, Elf_Data *data);

DESCRIPTION

These functions access and manipulate the data associated with a section descriptor, scn. When reading an existing file, a section will have a single data buffer associated

with it. A program may build a new section in pieces, how-

ever, composing the new data from multiple data buffers. For this reason, the data for a section should be viewed as a list of buffers, each of which is available through a data descriptor.

The elf_getdata() function lets a program step through a

section's data list. If the incoming data descriptor, data, is null, the function returns the first buffer associated

with the section. Otherwise, data should be a data descrip-

tor associated with scn, and the function gives the program access to the next data element for the section. If scn is

null or an error occurs, elf_getdata() returns a null

pointer.

The elf_getdata() function translates the data from file

representations into memory representations (see

elf32_xlatetof(3ELF)) and presents objects with memory data

types to the program, based on the file's class (see elf(3ELF)). The working library version (see

elf_version(3ELF)) specifies what version of the memory

structures the program wishes elf_getdata() to present.

The elf_newdata() function creates a new data descriptor for

a section, appending it to any data elements already associ-

ated with the section. As described below, the new data descriptor appears empty, indicating the element holds no

data. For convenience, the descriptor's type (d_type below)

is set to ELF_T_BYTE, and the version (d_version below) is

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ELF Library Functions elf_getdata(3ELF)

set to the working version. The program is responsible for setting (or changing) the descriptor members as needed. This

function implicitly sets the ELF_F_DIRTY bit for the

section's data (see elf_flagdata(3ELF)). If scn is null or

an error occurs, elf_newdata() returns a null pointer.

The elf_rawdata() function differs from elf_getdata() by

returning only uninterpreted bytes, regardless of the sec-

tion type. This function typically should be used only to retrieve a section image from a file being read, and then

only when a program must avoid the automatic data transla-

tion described below. Moreover, a program may not close or

disable (see elf_cntl(3ELF)) the file descriptor associated

with elf before the initial raw operation, because

elf_rawdata() might read the data from the file to ensure it

doesn't interfere with elf_getdata(). See elf_rawfile(3ELF)

for a related facility that applies to the entire file. When

elf_getdata() provides the right translation, its use is

recommended over elf_rawdata(). If scn is null or an error

occurs, elf_rawdata() returns a null pointer.

The Elf_Data structure includes the following members:

void *d_buf;

Elf_Type d_type;

size_t d_size;

off_t d_off;

size_t d_align;

unsigned d_version;

These members are available for direct manipulation by the program. Descriptions appear below.

d_buf A pointer to the data buffer resides here. A

data element with no data has a null pointer.

d_type This member's value specifies the type of the

data to which d_buf points. A section's type

determines how to interpret the section con-

tents, as summarized below.

d_size This member holds the total size, in bytes, of

the memory occupied by the data. This may differ from the size as represented in the file. The size will be zero if no data exist.

(See the discussion of SHT_NOBITS below for

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ELF Library Functions elf_getdata(3ELF)

more information.)

d_off This member gives the offset, within the sec-

tion, at which the buffer resides. This offset is relative to the file's section, not the memory object's.

d_align This member holds the buffer's required align-

ment, from the beginning of the section. That

is, d_off will be a multiple of this member's

value. For example, if this member's value is

4, the beginning of the buffer will be four-

byte aligned within the section. Moreover, the entire section will be aligned to the maximum of its constituents, thus ensuring appropriate alignment for a buffer within the section and within the file.

d_version This member holds the version number of the

objects in the buffer. When the library origi-

nally read the data from the object file, it

used the working version to control the trans-

lation to memory objects. Data Alignment As mentioned above, data buffers within a section have explicit alignment constraints. Consequently, adjacent buffers sometimes will not abut, causing ``holes'' within a section. Programs that create output files have two ways of dealing with these holes.

First, the program can use elf_fill() to tell the library

how to set the intervening bytes. When the library must gen-

erate gaps in the file, it uses the fill byte to initialize the data there. The library's initial fill value is 0, and

elf_fill() lets the application change that.

Second, the application can generate its own data buffers to occupy the gaps, filling the gaps with values appropriate

for the section being created. A program might even use dif-

ferent fill values for different sections. For example, it

could set text sections' bytes to no-operation instructions,

while filling data section holes with zero. Using this tech-

nique, the library finds no holes to fill, because the application eliminated them.

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ELF Library Functions elf_getdata(3ELF)

Section and Memory Types

The elf_getdata() function interprets sections' data accord-

ing to the section type, as noted in the section header

available through elf32_getshdr(). The following table shows

the section types and how the library represents them with

memory data types for the 32-bit file class. Other classes

would have similar tables. By implication, the memory data

types control translation by elf32_xlatetof(3ELF)

Section Type Elf_Type 32-bit Type

SHT_DYNAMIC ELF_T_DYN Elf32_Dyn

SHT_DYNSYM ELF_T_SYM Elf32_Sym

SHT_FINI_ARRAY ELF_T_ADDR Elf32_Addr

SHT_GROUP ELF_T_WORD Elf32_Word

SHT_HASH ELF_T_WORD Elf32_Word

SHT_INIT_ARRAY ELF_T_ADDR Elf32_Addr

SHT_NOBITS ELF_T_BYTE unsigned char

SHT_NOTE ELF_T_NOTE unsigned char

SHT_NULL none none

SHT_PREINIT_ARRAY ELF_T_ADDR Elf32_Addr

SHT_PROGBITS ELF_T_BYTE unsigned char

SHT_REL ELF_T_REL Elf32_Rel

SHT_RELA ELF_T_RELA Elf32_Rela

SHT_STRTAB ELF_T_BYTE unsigned char

SHT_SYMTAB ELF_T_SYM Elf32_Sym

SHT_SUNW_comdat ELF_T_BYTE unsigned char

SHT_SUNW_move ELF_T_MOVE Elf32_Move (sparc)

SHT_SUNW_move ELF_T_MOVEP Elf32_Move (ia32)

SHT_SUNW_syminfo ELF_T_SYMINFO Elf32_Syminfo

SHT_SUNW_verdef ELF_T_VDEF Elf32_Verdef

SHT_SUNW_verneed ELF_T_VNEED Elf32_Verneed

SHT_SUNW_versym ELF_T_HALF Elf32_Versym

other ELF_T_BYTE unsigned char

The elf_rawdata() function creates a buffer with type

ELF_T_BYTE.

As mentioned above, the program's working version controls what structures the library creates for the application. The library similarly interprets section types according to the versions. If a section type belongs to a version newer than the application's working version, the library does not translate the section data. Because the application cannot know the data format in this case, the library presents an

untranslated buffer of type ELF_T_BYTE, just as it would for

an unrecognized section type.

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ELF Library Functions elf_getdata(3ELF)

A section with a special type, SHT_NOBITS, occupies no space

in an object file, even when the section header indicates a

non-zero size. elf_getdata() and elf_rawdata() work on such

a section, setting the data structure to have a null buffer pointer and the type indicated above. Although no data are

present, the d_size value is set to the size from the sec-

tion header. When a program is creating a new section of

type SHT_NOBITS, it should use elf_newdata() to add data

buffers to the section. These empty data buffers should have

the d_size members set to the desired size and the d_buf

members set to NULL.

EXAMPLES

Example 1 A sample program of calling elf_getdata().

The following fragment obtains the string table that holds section names (ignoring error checking). See

elf_strptr(3ELF) for a variation of string table handling.

ehdr = elf32_getehdr(elf);

scn = elf_getscn(elf, (size_t)ehdr->e_shstrndx);

shdr = elf32_getshdr(scn);

if (shdr->sh_type != SHT_STRTAB)

{ /* not a string table */ } data = 0;

if ((data = elf_getdata(scn, data)) == 0 || data->d_size == 0)

{ /* error or no data */ }

The e_shstrndx member in an ELF header holds the section

table index of the string table. The program gets a section descriptor for that section, verifies it is a string table, and then retrieves the data. When this fragment finishes,

data->d_buf points at the first byte of the string table,

and data->d_size holds the string table's size in bytes.

ATTRIBUTES

See attributes(5) for descriptions of the following attri-

butes:

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ELF Library Functions elf_getdata(3ELF)

____________________________________________________________

| ATTRIBUTE TYPE | ATTRIBUTE VALUE |

|_____________________________|_____________________________|

| Interface Stability | Committed |

|_____________________________|_____________________________|

| MT-Level | MT-Safe |

|_____________________________|_____________________________|

Manual Pages for UNIX Operating System command usage for man elf_getdata

ELF Library Functions elf_getdata(3ELF)

NAME

elf_getdata, elf_newdata, elf_rawdata - get section data

SYNOPSIS

Elf_Data *elf_getdata(Elf_Scn *scn, Elf_Data *data);

DESCRIPTION

The elf_getdata() function lets a program step through a

null or an error occurs, elf_getdata() returns a null

The elf_getdata() function translates the data from file

structures the program wishes elf_getdata() to present.

ELF Library Functions elf_getdata(3ELF)

The elf_rawdata() function differs from elf_getdata() by

doesn't interfere with elf_getdata(). See elf_rawfile(3ELF)

elf_getdata() provides the right translation, its use is

ELF Library Functions elf_getdata(3ELF)

ELF Library Functions elf_getdata(3ELF)

The elf_getdata() function interprets sections' data accord-

ELF Library Functions elf_getdata(3ELF)

non-zero size. elf_getdata() and elf_rawdata() work on such

EXAMPLES

Example 1 A sample program of calling elf_getdata().

if ((data = elf_getdata(scn, data)) == 0 || data->d_size == 0)

ATTRIBUTES

ELF Library Functions elf_getdata(3ELF)

| ATTRIBUTE TYPE | ATTRIBUTE VALUE |

SEE ALSO

Elf_Data elf_getdata(Elf_Scn scn, Elf_Data *data);