A simple test confirms this:

$ cat hello.c
#include <stdio.h>
int main() { printf("Hello, World!\n"); return 0; }
$ gcc -o hello hello.c
$ nm --undefined-only hello
                 w _Jv_RegisterClasses
                 w __gmon_start__
                 U __libc_start_main@@GLIBC_2.2.5
                 U puts@@GLIBC_2.2.5

My code calls printf(), but the resulting executable actually calls puts()!

You need to override both puts() and printf() to catch all cases. Another option is to recompile using -fno-builtin-printf, but that’s probably defeating the purpose of using LD_PRELOAD in the first place.

I need to dump all debugging messages sent to console to a file/memory. At least three solutions are available:
1. Deploy wrapped printf all over the system. Our codes are from different team/company, different wrapper functions are used to output to console, so unify them is a little difficult (even inside our team, due to historical reason, printf of system library and wrappers are mix-used, NOT well organized!)
2. Touch UART driver: it’s a good solution, but we don’t want it. No reason.
3. Hook into printf: I find the solution here :-)

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