Including edk2-libc in efi shell application - libc

Question

How would one approach adding support for https://github.com/tianocore/edk2-libc, say I want to include stdio and use printf in my edk2 application? I followed StdLib/Readme.txt, and am able to successfully build examples in the AppPkg, however, when I try to add StdLib to my project I get errors like these:
LibString.lib(Searching.obj) : error LNK2005: strspn already defined in LibString.lib(Searching.obj)
LibCtype.lib(CClass.obj) : error LNK2005: isspace already defined in LibCtype.lib(CClass.obj)
(...)
LibC.lib(Main.obj) : error LNK2001: unresolved external symbol main
I do have the boilerplate (!include StdLib/StdLib.inc) added to my dsc file and in inf, I have StdLib.dec added to Packages and LibC and LibStdio added to LibraryClasses. I am using VS2017 toolchain for compilation and am using edk2-stable202108 release.

Answer 1

I was able to achieve this using below configuration for Hello Application of AppPkg.
Hello.inf
[Defines]
INF_VERSION = 0x00010006
BASE_NAME = Hello
FILE_GUID = a912f198-7f0e-4803-b908-b757b806ec83
MODULE_TYPE = UEFI_APPLICATION
VERSION_STRING = 0.1
ENTRY_POINT = ShellCEntryLib
#
# VALID_ARCHITECTURES = IA32 X64
#
[Sources]
Hello.c
[Packages]
MdePkg/MdePkg.dec
ShellPkg/ShellPkg.dec
StdLib/StdLib.dec
[LibraryClasses]
UefiLib
ShellCEntryLib
BaseLib
BaseMemoryLib
MemoryAllocationLib
LibStdLib
LibStdio
LibString
DevConsole
Hello.c
#include <Uefi.h>
#include <Library/UefiLib.h>
#include <Library/ShellCEntryLib.h>
#include <stdio.h>
int
main (
IN int Argc,
IN char **Argv
)
{
printf("Hello, world!\n");
return 0;
}
What I have understood is that LibC has ShellAppMain() defined in it which internally calls extern main(). So You need to provide definition of main() in your source just like I did in Hello.c