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. Thanks.
Bruce Hoult via llvm-dev
2015-Dec-05 21:25 UTC
[llvm-dev] How to call C function 'malloc' ?
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)"}
On Thu, Dec 3, 2015 at 4:03 PM, AllenShow via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> 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.
> Thanks.
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
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> On Dec 6, 2015, at 10:20 AM, AllenShow <xiulunlin at gmail.com> wrote: > > Thanks for you answer. > Actually I have tried like this, however, I want to know how could I implement this Just-in-time with ExecutionEngineer. > I have no idea how to make EE recognise libgcc.dylib. >> On Dec 6, 2015, at 5:25 AM, Bruce Hoult <bruce at hoult.org <mailto:bruce at hoult.org>> wrote: >> >> 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)"} >> >> >> >> On Thu, Dec 3, 2015 at 4:03 PM, AllenShow via llvm-dev <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote: >> 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. >> Thanks. >> _______________________________________________ >> LLVM Developers mailing list >> llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org> >> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev <http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev> >> >-------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20151206/f2f7b91e/attachment.html>