"tiny" printf is derived from _vfprintf_r in libc/stdio/nano-vfprintf.c.
"tiny" puts has been implemented so that it just calls write, without
any other processing.
Support for buffering, reentrancy and streams has been removed from
these functions to achieve reduced code size.
This reduced code size implementation of printf and puts can be enabled
in an application by passing "--wrap printf" and "--wrap puts" to the
GNU linker. This will replace references to "printf" and "puts" in user
code with "__wrap_printf" and "__wrap_puts" respectively.
If there is no implementation of these __wrap* functions in user code,
these "tiny" printf and puts implementations will be linked into the
final executable.
The wrapping mechanism is supposed to be invisible to the user:
- A GCC wrapper option such as "-mtiny-printf" will be added to alias
these wrap commands.
- If the user is unaware of the "tiny" implementation, and chooses to
implement their own __wrap_printf and __wrap_puts, their own
implementation will be automatically chosen over the "tiny" printf and
puts from the library.
Newlib must be configured with --enable-newlib-nano-formatted-io for
the "tiny" printf and puts functions to be built into the library.
Code size reduction examples:
printf("Hello World\n")
baseline - msp430-elf-gcc gcc-8_3_0-release
text data bss
5638 214 26
"tiny" puts enabled
text data bss
714 90 20
printf("Hello %d\n", a)
baseline - msp430-elf-gcc gcc-8_3_0-release
text data bss
10916 614 28
"tiny" printf enabled
text data bss
4632 280 20
Joel Sherrill
Jozef Lawrynowicz
Jeff Johnston
DJ Delorie