question about some terms

question about some terms

[loody]

Dear all:
There are some terms I cannot figure them out clearly.
1. relocatable file:
    (are they *.a and *.o files)
2. executable file
    (are they *.out files)
3. shared object file
    (are they *.so files)
4. Dynamically loaded libraries
    (what is the difference between 3 and 4)
thanks for your help,
miloody

Re: question about some terms

[Cary Coutant]

> There are some terms I cannot figure them out clearly.

There's a bit of fuzziness in these terms, but in general, you're pretty close.

> 1. relocatable file:
>    (are they *.a and *.o files)

More accurately, .a files are archive (or static) libraries, whose
members are relocatable objects (.o files).

> 2. executable file
>    (are they *.out files)

These are the output of a normal link (i.e., no -r option and no
-shared option). The ".out" extension is a bit ambiguous, as "a.out"
is both the traditional default output file name used by the Unix
assembler (usually a relocatable object, but traditionally the
assembler could also produce an executable file), and the default
output file name used by the linker. Normally an executable file has
been linked, has an entry point, and may or may not have dependencies
on shared objects (shared libraries).

> 3. shared object file
>    (are they *.so files)

Yes. Also called shared libraries or dynamic-link libraries (DLLs).

> 4. Dynamically loaded libraries
>    (what is the difference between 3 and 4)

In general, a dynamically-loaded library is a shared library that is
loaded during program execution via dlopen() (or equivalent), as
opposed to one that is listed as a dependency (directly or indirectly)
on the executable.

-cary

Re: question about some terms

[loody]

Hi:
2009/5/13 Cary Coutant <ccoutant@google.com>:
>> There are some terms I cannot figure them out clearly.
>
> There's a bit of fuzziness in these terms, but in general, you're pretty close.
>
>> 1. relocatable file:
>>    (are they *.a and *.o files)
>
> More accurately, .a files are archive (or static) libraries, whose
> members are relocatable objects (.o files).
>
>> 2. executable file
>>    (are they *.out files)
>
> These are the output of a normal link (i.e., no -r option and no
> -shared option). The ".out" extension is a bit ambiguous, as "a.out"
> is both the traditional default output file name used by the Unix
> assembler (usually a relocatable object, but traditionally the
> assembler could also produce an executable file), and the default
> output file name used by the linker. Normally an executable file has
> been linked, has an entry point, and may or may not have dependencies
> on shared objects (shared libraries).
>
>> 3. shared object file
>>    (are they *.so files)
>
> Yes. Also called shared libraries or dynamic-link libraries (DLLs).
>
>> 4. Dynamically loaded libraries
>>    (what is the difference between 3 and 4)
>
> In general, a dynamically-loaded library is a shared library that is
> loaded during program execution via dlopen() (or equivalent), as
> opposed to one that is listed as a dependency (directly or indirectly)
> on the executable.
>
> -cary
thanks for your kind help.
BTW, while reading ld and compare it with some sd scripts.
I saw some sections that I have no idea what it mean.
1. .sbss
2. .scommon
3. .sdata
4. .gptab
5. .lib8
6. .lit4
7. .reginfo
Those are not symbol that will be used under program.
it seems the default sections that will be generated by compiler.
Does there any document provide the whole list and purpose of them?
appreciate your kind help,
miloody

Re: question about some terms

[Ian Lance Taylor]

loody <miloody@gmail.com> writes:

> BTW, while reading ld and compare it with some sd scripts.
> I saw some sections that I have no idea what it mean.
> 1. .sbss

Small local zero-initialized global or static variables.  The definition
of "small" varies by target.  On some targets, notably MIPS targets when
not generating PIC, it can be controlled by the -G option to the
compiler and linker.

> 2. .scommon

Small common variables.

> 3. .sdata

Small initialized global or static variables.

> 4. .gptab

A MIPS specific section which holds an array of entries.  Each entry has
two values: a -G argument and the size of the small data if that -G
argument is used.  The linker can use this to pick the optimal -G value
(MIPS permits a total of 65536 bytes in the small data sections).  I
don't know whether the GNU linker actually implements this optimization.

> 5. .lib8

Did you mean .lit8?  That is section used on Alpha and MIPS to hold 8
byte literals.  The address of the literal values is unimportant, and
the linker is permitted to combine identical 8 byte literals.  This is a
size and target specific implementation of the idea that ELF later
generalized into SHF_MERGE sections.  .lit8 was introduced in ECOFF.  It
is mostly used to hold floating point constants.

> 6. .lit4

Like .lit8, but for 4 byte literals.  This one is not used very much.

> 7. .reginfo

Used to describe which registers are used by functions in the file.
This is mainly for some MIPS optimization tools which were written at
SGI.  The GNU tools generate it but I don't think they use it for
anything.

> Does there any document provide the whole list and purpose of them?
> appreciate your kind help,

Try the MIPS ELF ABI.

Ian