How to call C function 'malloc' ?

Hi, everyone.
I am new to llvm and I want to use C function “malloc" and “free" to do heap allocation, but It seems it is not a built-in function like ‘’printf” so I got an error “Unknown extern function”.
I use ExecutionEngineer to run my main function and how should I do to make EE link the C library I want.

The answer to such questions is usually best obtained by looking at what clang does. See below.

$ cat foo.c

#include <stdlib.h>

void* foo(int i){return malloc(i);}

$ clang -emit-llvm -S foo.c

$ cat foo.ll

; ModuleID = ‘foo.c’

target datalayout = “e-m:o-i64:64-f80:128-n8:16:32:64-S128”

target triple = “x86_64-apple-macosx10.10.0”

; Function Attrs: nounwind ssp uwtable

define i8* @foo(i32 %i) #0 {

%1 = alloca i32, align 4

store i32 %i, i32* %1, align 4

%2 = load i32* %1, align 4

%3 = sext i32 %2 to i64

%4 = call i8* @malloc(i64 %3)

ret i8* %4


declare i8* @malloc(i64) #1

attributes #0 = { nounwind ssp uwtable “less-precise-fpmad”=“false” “no-frame-pointer-elim”=“true” “no-frame-pointer-elim-non-leaf” “no-infs-fp-math”=“false” “no-nans-fp-math”=“false” “stack-protector-buffer-size”=“8” “unsafe-fp-math”=“false” “use-soft-float”=“false” }

attributes #1 = { “less-precise-fpmad”=“false” “no-frame-pointer-elim”=“true” “no-frame-pointer-elim-non-leaf” “no-infs-fp-math”=“false” “no-nans-fp-math”=“false” “stack-protector-buffer-size”=“8” “unsafe-fp-math”=“false” “use-soft-float”=“false” }

!llvm.ident = !{!0}

!0 = metadata !{metadata !“Apple LLVM version 6.0 (clang-600.0.56) (based on LLVM 3.5svn)”}