CODEWITHSUNDEEP
c++cembedded
Ali Hamdy
Ali Hamdy

Reputation: 63

if we had a single file project that contained all the code can we not use the linker?

Linker question:

if I had a file. c that has no includes at all, would we still need a linker?

Upvotes: 2

Views: 1138

Answers (4)

Clifford
Clifford

Reputation: 93476

Despite its name the linker is properly a "linker/locater". It performs two functions - 1) linking object code, 2) determining where in memory the data and code elements exist.

The object code out of the compiler is not "located" even if it has no unresolved links.

Also even if you have the simplest possible valid code:

int main(){ return 0; }

with no includes, the linker will normally implicitly link the C runtime start-up, which is required to do everything necessary before running main(). That may be very little. On some target such as ARM Cortex-M you can in fact run C code directly from the reset vector so long as you don't assume static initialisation or complete library support. So it is possible to write the reset code entirely in C, but you probably still need code to initialise the vector table with the reset handler (your C start-up function) and the initial stack pointer. On Cortex-M that can be done using in-line assembler perhaps, but it is all rather cumbersome and unnecessary and does not forgo the linker.

Upvotes: 0

Devolus
Devolus

Reputation: 22094

You can create a project, which has no typical C startup code, in which case, you may not even have a main(). However, you still need a linker, because the linker creates the required executable file format for the given architecture.

It also will set the entrypoint, where the actual execution starts. So you can omit the standard libraries, and create a binary, which is completly void of any C functions, but you still need the linker to actually make a runable binary.

The object file format, generated by the compiler, is very different to the executable file format, because it only provides all information, that is required for the linker.

Upvotes: 1

h0tst3w
h0tst3w

Reputation: 114

Yes. The linker does more than merely link the files. Check out this resource for more info: https://en.wikibooks.org/wiki/C%2B%2B_Programming/Programming_Languages/C%2B%2B/Code/Compiler/Linker#:~:text=The%20linker%20is%20a%20program,translation%20unit%20have%20external%20linkage.

Believe it or not, multiple libraries can be referenced by default. So, even if you don't #includea resource, the compiler may have to internally link or reference something outside of the translation unit. There are also redundancies and other considerations that are "eliminated" by the compiler.

Upvotes: 0

Eric Postpischil
Eric Postpischil

Reputation: 222933

Although the linker is so-named because it links together multiple object files, it performs other functions as well. It may resolve addresses that were left incomplete by the compiler. It produces a program in an executable file format that the system’s program loader can read and load, and that format may differ from that of object modules. Specifics depend on the operating system and build tools.

Further, to have a complete program in one source file, you must provide not just the main routine you are familiar with from C and C++ but also the true start of the program, the entry point that the program loader starts execution at, and you must provide implementations for all functions you use in the program, such as invocations of system services via special trap or system-call instructions to read and write data.

Upvotes: 4

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