gen_provides: export per-variant TLS symbol offsets to sketches

Add an option to export TLS symbol offsets to an assembly wrapper in
each board's variant folder, so that they can be used at core compile
time. This will allow 'errno' and other thread-local symbols to be
properly resolved in the sketches.

Also export the '__aebabi_read_tp' function on ARM targets, which is
used by the compiler-generated TLS code to compute absolute symbol
addresses.

Signed-off-by: Luca Burelli <l.burelli@arduino.cc>

Author: pillo79

cores/arduino/llext_wrappers.c

@@ -62,6 +62,11 @@
 		__real_##name(a);                                                                          \
 	}
 
+#ifdef CONFIG_ARM
+/* ARM EABI thread pointer access */
+W0(size_t, __aeabi_read_tp)
+#endif
+
 /* string.h */
 W3(void *, memcpy, void *, const void *, size_t)
 W3(void *, memmove, void *, const void *, size_t)

extra/build.sh

@@ -102,6 +102,7 @@ cp ${BUILD_DIR}/zephyr/.config firmwares/zephyr-$variant.config
 
 # Generate the provides.ld file for linked builds
 echo "Generating exported symbol scripts"
+extra/gen_provides.py "${BUILD_DIR}/zephyr/zephyr.elf" -T > ${VARIANT_DIR}/tls-syms.S
 extra/gen_provides.py "${BUILD_DIR}/zephyr/zephyr.elf" -L > ${VARIANT_DIR}/syms-dynamic.ld
 extra/gen_provides.py "${BUILD_DIR}/zephyr/zephyr.elf" -LF \
 	"+kheap_llext_heap" \

extra/gen_provides.py

@@ -122,17 +122,29 @@ def main():
     argparser.add_argument('-F', '--funcs',
             action='store_true',
             help='Extract all public functions')
+    argparser.add_argument('-T', '--tls-defs',
+            action='store_true',
+            help='Extract TLS symbol offsets to a .S file')
     argparser.add_argument('file',
             help='ELF file to parse')
     argparser.add_argument('syms', nargs='*',
             help='Symbols to export')
 
     args = argparser.parse_intermixed_args()
 
+    wants_provides = bool(args.syms or args.funcs or args.llext)
+    if wants_provides and args.tls_defs:
+        sys.stderr.write("Cannot generate TLS defs when also generating PROVIDEs.\n")
+        sys.exit(1)
+    elif not wants_provides and not args.tls_defs:
+        sys.stderr.write("Nothing specified for export.\n")
+        sys.exit(1)
+
     exact_syms = set()
     regex_syms = set()
     deref_syms = set()
     sized_syms = set()
+    tls_syms = set() # tuple of (name, value, size)
     rename_map = {}
     for sym in args.syms:
         sym_class = None
@@ -184,6 +196,11 @@ def main():
         fail = False
 
         for name, sym in all_syms.items():
+            if sym['st_info']['type'] == 'STT_TLS':
+                # Collect TLS symbol information, ignore for PROVIDEs
+                tls_syms.add((name, sym['st_value'], sym['st_size']))
+                continue
+
             value = None
             comment = []
             if name in exact_syms or any(re.match(r, name) for r in regex_syms):
@@ -232,20 +249,46 @@ def main():
  */
 """)
 
-        if not out_syms:
-            print("/* No symbols found matching the criteria */")
-            sys.stderr.write("warning: no symbols found matching the criteria.\n")
-        else:
-            sym_comment = nul_comment = ""
-            for name, (value, comments) in sorted(out_syms.items(), key=lambda x: x[0]):
-                if args.verbose:
-                    comment = ', '.join(sorted(comments))
-                    sym_comment = f"/* {comment} */"
-                    nul_comment = f" ({comment})"
-                if value:
-                    print(f"PROVIDE({name} = {value:#010x});{sym_comment}")
-                else:
-                    print(f"/* NULL {name}{nul_comment} */")
+        if wants_provides:
+            if not out_syms:
+                print("/* No symbols found matching the criteria */")
+                sys.stderr.write("warning: no symbols found matching the criteria.\n")
+            else:
+                sym_comment = nul_comment = ""
+                for name, (value, comments) in sorted(out_syms.items(), key=lambda x: x[0]):
+                    if args.verbose:
+                        comment = ', '.join(sorted(comments))
+                        sym_comment = f"/* {comment} */"
+                        nul_comment = f" ({comment})"
+                    if value:
+                        print(f"PROVIDE({name} = {value:#010x});{sym_comment}")
+                    else:
+                        print(f"/* NULL {name}{nul_comment} */")
+
+        if args.tls_defs:
+            # ARM and AArch64 use '@' as a line-comment character in GAS, so the
+            # assembler requires '%' as the type prefix there.  All other targets use '@'.
+            prefix = '%' if elf['e_machine'] in ('EM_ARM', 'EM_AARCH64') else '@'
+
+            # The TLS Variant 1 layout (used by ARM/AArch64) places a Thread
+            # Control Block (TCB) before the TLS data.  The thread pointer
+            # returned by __aeabi_read_tp() points to the TCB, so the actual
+            # runtime address of a TLS variable must be offset by that size.
+            #
+            # TCB is 2 pointers: 8 bytes on 32-bit, 16 bytes on 64-bit.
+            # See zephyr/arch/arm/core/tls.c: arch_tls_stack_setup().
+            tcb_size = (elf.elfclass // 8) * 2
+            print(f"/* Offsets include {tcb_size} bytes for TCB data */")
+
+            # Sort by offset first, then size
+            for name, offset, size in sorted(tls_syms, key=lambda x: (x[1], x[2])):
+                offset += tcb_size
+                print(
+                    f"\n/* TLS offset {offset:#x}: {name} ({size} bytes) */\n"
+                    f".global {name}\n"
+                    f".type {name}, {prefix}tls_object\n"
+                    f".set {name}, {offset}"
+                )
 
 #-------------------------------------------------------------------------------
 if __name__ == '__main__':

loader/llext_exports.c

@@ -289,6 +289,10 @@ EXPORT_SYMBOL(ring_buf_area_finish);
 #endif
 
 EXPORT_SYMBOL(sys_clock_cycle_get_32);
+
+#if defined(CONFIG_ARM)
+extern uint32_t __aeabi_read_tp(void);
+EXPORT_LIBC_SYM(__aeabi_read_tp);
 FORCE_EXPORT_SYM(__aeabi_dcmpun);
 FORCE_EXPORT_SYM(__aeabi_dcmple);
 FORCE_EXPORT_SYM(__aeabi_d2lz);
@@ -318,6 +322,7 @@ FORCE_EXPORT_SYM(__aeabi_idivmod);
 FORCE_EXPORT_SYM(__aeabi_ldivmod);
 FORCE_EXPORT_SYM(__aeabi_ul2f);
 FORCE_EXPORT_SYM(__aeabi_dcmpge);
+#endif
 
 #if defined (CONFIG_CPP)
 FORCE_EXPORT_SYM(__cxa_pure_virtual);