NetBSD specific things needed by the shared library support.
This commit is contained in:
kristerw
parent
4b50867128
commit
e39ec0adc1
|
|
@ -0,0 +1,209 @@
|
|||
/* NetBSD-specific values for a.out files */
|
||||
|
||||
/* XXX This file is mostly copied from the sunos counterpart. Most, but
|
||||
* not all, Sun OS specific things has ben changed, so some comments may
|
||||
* be slightly wrong. */
|
||||
|
||||
/* Size of the text section. */
|
||||
#define N_TXTSIZE(x) \
|
||||
(N_IS_QMAGIC (x) ? (x).a_text - EXEC_BYTES_SIZE : \
|
||||
(N_MAGIC(x) != ZMAGIC) ? (x).a_text : \
|
||||
N_HEADER_IN_TEXT(x) ? \
|
||||
(x).a_text - EXEC_BYTES_SIZE: \
|
||||
(x).a_text \
|
||||
)
|
||||
|
||||
/* Offset in an a.out of the start of the text section. */
|
||||
#define N_TXTOFF(x) \
|
||||
(N_MAGIC(x) != ZMAGIC ? EXEC_BYTES_SIZE : \
|
||||
N_HEADER_IN_TEXT(x) ? \
|
||||
EXEC_BYTES_SIZE : \
|
||||
ZMAGIC_DISK_BLOCK_SIZE \
|
||||
)
|
||||
|
||||
/* The address of the data segment in virtual memory. */
|
||||
#define N_TXTADDR(x) \
|
||||
(N_IS_QMAGIC (x) ? TARGET_PAGE_SIZE + EXEC_BYTES_SIZE : \
|
||||
N_MAGIC(x) != ZMAGIC ? 0 : \
|
||||
N_HEADER_IN_TEXT(x) ? \
|
||||
TEXT_START_ADDR + EXEC_BYTES_SIZE : \
|
||||
TEXT_START_ADDR \
|
||||
)
|
||||
|
||||
/* When a file is linked against a shared library on NetBSD, the
|
||||
dynamic bit in the exec header is set, and the first symbol in the
|
||||
symbol table is __DYNAMIC. Its value is the address of the
|
||||
following structure. */
|
||||
struct external_netbsd_dynamic
|
||||
{
|
||||
/* The version number of the structure. NetBSD creates files
|
||||
with version number 8, which is what this structure is based on. */
|
||||
bfd_byte d_version[4];
|
||||
/* The virtual address of a 24 byte structure used in debugging.
|
||||
The contents are filled in at run time by ld.so. */
|
||||
bfd_byte d_debug[4];
|
||||
/* The virtual address of another structure with information about
|
||||
how to relocate the executable at run time. */
|
||||
bfd_byte d_un[4];
|
||||
/* compat - now in crt_ldso */
|
||||
bfd_byte d_entry[4];
|
||||
};
|
||||
|
||||
/* The size of the debugging structure pointed to by the debugger
|
||||
field of __DYNAMIC. */
|
||||
#define EXTERNAL_NETBSD_DYNAMIC_DEBUGGER_SIZE (24)
|
||||
|
||||
/* The structure pointed to by the d_un field of __DYNAMIC. As far
|
||||
as I can tell, most of the addresses in this structure are offsets
|
||||
within the file, but some are actually virtual addresses. */
|
||||
struct internal_section_dispatch_table
|
||||
{
|
||||
/* Linked list of loaded objects. This is filled in at runtime by
|
||||
ld.so and probably by dlopen. */
|
||||
unsigned long sdt_loaded;
|
||||
|
||||
/* The address of the list of names of shared objects which must be
|
||||
included at runtime. Each entry in the list is 16 bytes: the 4
|
||||
byte address of the string naming the object (e.g., for -lc this
|
||||
is "c"); 4 bytes of flags--the high bit is whether to search for
|
||||
the object using the library path; the 2 byte major version
|
||||
number; the 2 byte minor version number; the 4 byte address of
|
||||
the next entry in the list (zero if this is the last entry). The
|
||||
version numbers seem to only be non-zero when doing library
|
||||
searching. */
|
||||
unsigned long sdt_sods;
|
||||
|
||||
/* The address of the path to search for the shared objects which
|
||||
must be included. This points to a string in PATH format which
|
||||
is generated from the -L arguments to the linker. According to
|
||||
the man page, ld.so implicitly adds ${LD_LIBRARY_PATH} to the
|
||||
beginning of this string and /lib:/usr/lib to the end. The string
|
||||
is terminated by a null byte. This field is zero if there is no
|
||||
additional path. */
|
||||
unsigned long sdt_paths;
|
||||
|
||||
/* The address of the global offset table. This appears to be a
|
||||
virtual address, not a file offset. The first entry in the
|
||||
global offset table seems to be the virtual address of the
|
||||
_dynamic structure (the same value as the __DYNAMIC symbol).
|
||||
The global offset table is used for PIC code to hold the
|
||||
addresses of variables. A dynamically linked file which does not
|
||||
itself contain PIC code has a four byte global offset table. */
|
||||
unsigned long sdt_got;
|
||||
|
||||
/* The address of the procedure linkage table. This appears to be a
|
||||
virtual address, not a file offset.
|
||||
|
||||
On a SPARC, the table is composed of 12 byte entries, each of
|
||||
which consists of three instructions. The first entry is
|
||||
sethi %hi(0),%g1
|
||||
jmp %g1
|
||||
nop
|
||||
These instructions are changed by ld.so into a jump directly into
|
||||
ld.so itself. Each subsequent entry is
|
||||
save %sp, -96, %sp
|
||||
call <address of first entry in procedure linkage table>
|
||||
<reloc_number | 0x01000000>
|
||||
The reloc_number is the number of the reloc to use to resolve
|
||||
this entry. The reloc will be a JMP_SLOT reloc against some
|
||||
symbol that is not defined in this object file but should be
|
||||
defined in a shared object (if it is not, ld.so will report a
|
||||
runtime error and exit). The constant 0x010000000 turns the
|
||||
reloc number into a sethi of %g0, which does nothing since %g0 is
|
||||
hardwired to zero.
|
||||
|
||||
When one of these entries is executed, it winds up calling into
|
||||
ld.so. ld.so looks at the reloc number, available via the return
|
||||
address, to determine which entry this is. It then looks at the
|
||||
reloc and patches up the entry in the table into a sethi and jmp
|
||||
to the real address followed by a nop. This means that the reloc
|
||||
lookup only has to happen once, and it also means that the
|
||||
relocation only needs to be done if the function is actually
|
||||
called. The relocation is expensive because ld.so must look up
|
||||
the symbol by name.
|
||||
|
||||
The size of the procedure linkage table is given by the ld_plt_sz
|
||||
field. */
|
||||
unsigned long sdt_plt;
|
||||
|
||||
/* The address of the relocs. These are in the same format as
|
||||
ordinary relocs. Symbol index numbers refer to the symbols
|
||||
pointed to by ld_stab. I think the only way to determine the
|
||||
number of relocs is to assume that all the bytes from ld_rel to
|
||||
ld_hash contain reloc entries. */
|
||||
unsigned long sdt_rel;
|
||||
|
||||
/* The address of a hash table of symbols. The hash table has
|
||||
roughly the same number of entries as there are dynamic symbols;
|
||||
I think the only way to get the exact size is to assume that
|
||||
every byte from ld_hash to ld_stab is devoted to the hash table.
|
||||
|
||||
Each entry in the hash table is eight bytes. The first four
|
||||
bytes are a symbol index into the dynamic symbols. The second
|
||||
four bytes are the index of the next hash table entry in the
|
||||
bucket. The ld_buckets field gives the number of buckets, say B.
|
||||
The first B entries in the hash table each start a bucket which
|
||||
is chained through the second four bytes of each entry. A value
|
||||
of zero ends the chain.
|
||||
|
||||
The hash function is simply
|
||||
h = 0;
|
||||
while (*string != '\0')
|
||||
h = (h << 1) + *string++;
|
||||
h &= 0x7fffffff;
|
||||
|
||||
To look up a symbol, compute the hash value of the name. Take
|
||||
the modulos of hash value and the number of buckets. Start at
|
||||
that entry in the hash table. See if the symbol (from the first
|
||||
four bytes of the hash table entry) has the name you are looking
|
||||
for. If not, use the chain field (the second four bytes of the
|
||||
hash table entry) to move on to the next entry in this bucket.
|
||||
If the chain field is zero you have reached the end of the
|
||||
bucket, and the symbol is not in the hash table. */
|
||||
unsigned long sdt_hash;
|
||||
|
||||
/* The address of the symbol table. This is a list of
|
||||
external_nzlist structures. The string indices are relative to
|
||||
the ld_symbols field. I think the only way to determine the
|
||||
number of symbols is to assume that all the bytes between ld_stab
|
||||
and ld_symbols are external_nzlist structures. */
|
||||
unsigned long sdt_nzlist;
|
||||
|
||||
/* Unusued */
|
||||
unsigned long sdt_filler2;
|
||||
|
||||
/* The number of buckets in the hash table. */
|
||||
unsigned long sdt_buckets;
|
||||
|
||||
/* The address of the symbol string table. The first string in this
|
||||
string table need not be the empty string. */
|
||||
unsigned long sdt_strings;
|
||||
|
||||
/* The size in bytes of the symbol string table. */
|
||||
unsigned long sdt_str_sz;
|
||||
|
||||
/* The size in bytes of the text segment. */
|
||||
unsigned long sdt_text_sz;
|
||||
|
||||
/* The size in bytes of the procedure linkage table. */
|
||||
unsigned long sdt_plt_sz;
|
||||
};
|
||||
|
||||
/* The external form of the structure. */
|
||||
struct external_netbsd_dynamic_link
|
||||
{
|
||||
bfd_byte sdt_loaded[4];
|
||||
bfd_byte sdt_sods[4];
|
||||
bfd_byte sdt_paths[4];
|
||||
bfd_byte sdt_got[4];
|
||||
bfd_byte sdt_plt[4];
|
||||
bfd_byte sdt_rel[4];
|
||||
bfd_byte sdt_hash[4];
|
||||
bfd_byte sdt_nzlist[4];
|
||||
bfd_byte sdt_filler2[4];
|
||||
bfd_byte sdt_buckets[4];
|
||||
bfd_byte sdt_strings[4];
|
||||
bfd_byte sdt_str_sz[4];
|
||||
bfd_byte sdt_text_sz[4];
|
||||
bfd_byte sdt_plt_sz[4];
|
||||
};
|
||||
Loading…
Reference in New Issue