tools/mpy_ld.py: Allow linking static libraries.

This commit introduces an additional symbol resolution mechanism to the
natmod linking process.  This allows the build scripts to look for required
symbols into selected libraries that are provided by the compiler
installation (libgcc and libm at the moment).

For example, using soft-float code in natmods, whilst technically possible,
was not an easy process and required some additional work to pull it off.
With this addition all the manual (and error-prone) operations have been
automated and folded into `tools/mpy_ld.py`.

Both newlib and picolibc toolchains are supported, albeit the latter may
require a bit of extra configuration depending on the environment the build
process runs on.  Picolibc's soft-float functions aren't in libm - in fact
the shipped libm is nothing but a stub - but they are inside libc.  This is
usually not a problem as these changes cater for that configuration quirk,
but on certain compilers the include paths used to find libraries in may
not be updated to take Picolibc's library directory into account.  The bare
metal RISC-V compiler shipped with the CI OS image (GCC 10.2.0 on Ubuntu
22.04LTS) happens to exhibit this very problem.

To work around that for CI builds, the Picolibc libraries' path is
hardcoded in the Makefile directives used by the linker, but this can be
changed by setting the PICOLIBC_ROOT environment library when building
natmods.

Signed-off-by: Volodymyr Shymanskyy <vshymanskyi@gmail.com>
Co-authored-by: Alessandro Gatti <a.gatti@frob.it>

2 files changed, 14 insertions, 0 deletions

diff --git a/examples/natmod/features2/Makefile b/examples/natmod/features2/Makefile
index 4fd23c6879..5ddb74087b 100644
--- a/examples/natmod/features2/Makefile
+++ b/examples/natmod/features2/Makefile
@@ -10,5 +10,8 @@ SRC = main.c prod.c test.py
 # Architecture to build for (x86, x64, armv7m, xtensa, xtensawin)
 ARCH = x64
 
+# Link with libm.a and libgcc.a from the toolchain
+LINK_RUNTIME = 1
+
 # Include to get the rules for compiling and linking the module
 include $(MPY_DIR)/py/dynruntime.mk
diff --git a/examples/natmod/features2/main.c b/examples/natmod/features2/main.c
index 22961aa494..5ce8e7b013 100644
--- a/examples/natmod/features2/main.c
+++ b/examples/natmod/features2/main.c
@@ -1,5 +1,6 @@
 /* This example demonstrates the following features in a native module:
     - using floats
+    - calling math functions from libm.a
     - defining additional code in Python (see test.py)
     - have extra C code in a separate file (see prod.c)
 */
@@ -10,6 +11,9 @@
 // Include the header for auxiliary C code for this module
 #include "prod.h"
 
+// Include standard library header
+#include <math.h>
+
 // Automatically detect if this module should include double-precision code.
 // If double precision is supported by the target architecture then it can
 // be used in native module regardless of what float setting the target
@@ -41,6 +45,12 @@ static mp_obj_t add_d(mp_obj_t x, mp_obj_t y) {
 static MP_DEFINE_CONST_FUN_OBJ_2(add_d_obj, add_d);
 #endif
 
+// A function that uses libm
+static mp_obj_t call_round(mp_obj_t x) {
+    return mp_obj_new_float_from_f(roundf(mp_obj_get_float_to_f(x)));
+}
+static MP_DEFINE_CONST_FUN_OBJ_1(round_obj, call_round);
+
 // A function that computes the product of floats in an array.
 // This function uses the most general C argument interface, which is more difficult
 // to use but has access to the globals dict of the module via self->globals.
@@ -74,6 +84,7 @@ mp_obj_t mpy_init(mp_obj_fun_bc_t *self, size_t n_args, size_t n_kw, mp_obj_t *a
     #if USE_DOUBLE
     mp_store_global(MP_QSTR_add_d, MP_OBJ_FROM_PTR(&add_d_obj));
     #endif
+    mp_store_global(MP_QSTR_round, MP_OBJ_FROM_PTR(&round_obj));
 
     // The productf function uses the most general C argument interface
     mp_store_global(MP_QSTR_productf, MP_DYNRUNTIME_MAKE_FUNCTION(productf));