CODEWITHSUNDEEP
cgccassemblycompilation
Elektito
Elektito

Reputation: 4155

Make gcc not issue a 'ret' instruction at the end of function

If I compile this piece of C code:

void _start() {
}

with this invocation of gcc:

gcc -nostdlib -Os -S foo.c

I get this assembly listing:

        .file   "foo.c"
        .section        .text.unlikely,"x"
LCOLDB0:
        .text
LHOTB0:
        .globl  __start
        .def    __start;        .scl    2;      .type   32;     .endef
__start:
        pushl   %ebp
        movl    %esp, %ebp
        popl    %ebp
        ret
        .section        .text.unlikely,"x"
LCOLDE0:
        .text
LHOTE0:
        .ident  "GCC: (GNU) 4.9.2"

As you see gcc has issued a 'ret' instruction at the end of the code. Is there a way to make it not to issue that?

Upvotes: 2

Views: 654

Answers (1)

Marc Glisse
Marc Glisse

Reputation: 7925

Calling __builtin_unreachable(); in your function tells gcc that it does not need to return at the end, since it will not reach the end.

Upvotes: 5

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