On: How to dismantle a compiler bomb

[derefr]

> according to the C standard, 'main' is not a reserved identifier!

In fact, main() is just a convention of libc. You can have C without libc. (Such as when writing a kernel!)

Now, attempting to link a standalone executable without a '_start' symbol, on the other hand...

[shakna → derefr]

> In fact, main() is just a convention of libc.

No, it's not just a convention. 'main' is defined as the execution entrypoint in at least the C11 [0], C90 [1] standards. Both have both these forms defined:

    int main(void) {}

    int main(int argc, char* argv[]) {}

You don't have to follow that convention, but then it becomes implementation-defined behaviour.

C without libc can still expect to have a main. One doesn't imply the other. It's just without a main, you also have to manually link to _start as well.

[0] http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf

[1] http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1256.pdf

[prattmic → derefr]

> Now, attempting to link a standalone executable without a '_start' symbol, on the other hand...

GNU ld and gold both support --entry to change the entry point. Alternatively, you can specify it in your linker script.

https://gist.github.com/prattmic/1f3618025aab52b0e90e88445b6...

    $ gcc -nostdlib -ffreestanding -Wl,--entry=foobar -o main main.S
    $ ./main; echo $?
    42