LLVM bytecode linked with with ld.lld gives segmentation fault - llvm

Question

I wrote a simple C program:
example.c:
int main() {
return 0;
}
Then converted it to .ll by using
clang -S -emit-llvm example.c
Which generated a example.ll file which looks like this:
; ModuleID = 'example.c'
source_filename = "example.c"
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-pc-linux-gnu"
; Function Attrs: noinline nounwind optnone uwtable
define dso_local i32 #main() #0 {
%1 = alloca i32, align 4
store i32 0, i32* %1, align 4
ret i32 0
}
attributes #0 = { noinline nounwind optnone uwtable "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "min-legal-vector-width"="0" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+fxsr,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }
!llvm.module.flags = !{!0}
!llvm.ident = !{!1}
!0 = !{i32 1, !"wchar_size", i32 4}
!1 = !{!"clang version 8.0.0-3 (tags/RELEASE_800/final)"}
Then I converted .ll file to .o by using:
llc -filetype=obj example.ll
And then I tried to link that file to make it executable by using:
ld.lld example.o -o example -e main
Which created an executable ./example.
Running example yields a segmentation fault
29185 segmentation fault (core dumped) ./example
objdump of example.o looks like this:
example.o: file format elf64-x86-64
Disassembly of section .text:
0000000000000000 <main>:
0: 55 push %rbp
1: 48 89 e5 mov %rsp,%rbp
4: c7 45 fc 00 00 00 00 movl $0x0,-0x4(%rbp)
b: 31 c0 xor %eax,%eax
d: 5d pop %rbp
e: c3 retq
And the executable looks like this:
example: file format elf64-x86-64
Disassembly of section .text:
0000000000201000 <main>:
201000: 55 push %rbp
201001: 48 89 e5 mov %rsp,%rbp
201004: c7 45 fc 00 00 00 00 movl $0x0,-0x4(%rbp)
20100b: 31 c0 xor %eax,%eax
20100d: 5d pop %rbp
20100e: c3 retq
I also tried linking the object file with ld but that also didn't work. Am I missing something. How can I make a llvm object file executable? Please note that none of the commands yielded any errors or warnings.

Answer 1

Well, this is not how you supposed to link the executable. E.g. entry point is supposed to be named "_start" and so on, so you're missing bunch of runtime initialization objects / libraries here.
Either link with clang (so, clang example.ll or clang example.o) or pass -v to clang invocation to obtain the proper linker cmdline.