Add linking step

Makefile

@@ -28,7 +28,10 @@ ASM_FILES := $(patsubst $(BUILD_DIR)/%.i,$(BUILD_DIR)/%.S,$(PREP_FILES))
 OBJ_FILES := $(patsubst $(BUILD_DIR)/%.S,$(BUILD_DIR)/%.o,$(ASM_FILES))
 
 .PHONY: build
-build: builddir preprocess compile assemble
+build: builddir preprocess compile assemble $(BUILD_DIR)/final.elf
+
+$(BUILD_DIR)/final.elf: $(OBJ_FILES)
+	$(CC) $(LDFLAGS) $^ -o $@
 
 $(BUILD_DIR)/%.i: $(SRC_DIR)/%.c
 	$(CC) $(CFLAGS) -E $^ -o $@

build/final.elf.map

@@ -0,0 +1,156 @@
+
+Discarded input sections
+
+ .text          0x00000000        0x0 build/main.o
+ .data          0x00000000        0x0 build/main.o
+ .bss           0x00000000        0x0 build/main.o
+ .group         0x00000000        0xc build/startup.o
+ .group         0x00000000        0xc build/startup.o
+ .group         0x00000000        0xc build/startup.o
+ .group         0x00000000        0xc build/startup.o
+ .group         0x00000000        0xc build/startup.o
+ .group         0x00000000        0xc build/startup.o
+ .text          0x00000000        0x0 build/startup.o
+ .data          0x00000000        0x0 build/startup.o
+ .bss           0x00000000        0x0 build/startup.o
+
+Memory Configuration
+
+Name             Origin             Length             Attributes
+flash            0x08000000         0x00080000         xr
+sram             0x20000000         0x00020000         xrw
+*default*        0x00000000         0xffffffff
+
+Linker script and memory map
+
+LOAD /nix/store/yr89i11mszv2az19r26l372zgaiivj1c-gcc-arm-embedded-12.3.rel1/bin/../lib/gcc/arm-none-eabi/12.3.1/../../../../arm-none-eabi/lib/libc_nano.a
+LOAD /nix/store/yr89i11mszv2az19r26l372zgaiivj1c-gcc-arm-embedded-12.3.rel1/bin/../lib/gcc/arm-none-eabi/12.3.1/libgcc.a
+LOAD build/main.o
+LOAD build/startup.o
+                0x20020000                        stack_start = (ORIGIN (sram) + LENGTH (sram))
+
+.isr_vector     0x08000000      0x198
+                0x08000000                        . = ALIGN (0x4)
+ *(.isr_vector)
+ .isr_vector    0x08000000      0x198 build/startup.o
+                0x08000000                interrupt_vector_table
+                0x08000198                        . = ALIGN (0x4)
+
+.text           0x08000198       0x84
+                0x08000198                        . = ALIGN (0x4)
+ *(.text)
+ *(.text.*)
+ .text.main     0x08000198       0x10 build/main.o
+                0x08000198                main
+ .text.init_memory
+                0x080001a8       0x64 build/startup.o
+                0x080001a8                init_memory
+ .text.reset    0x0800020c       0x10 build/startup.o
+                0x0800020c                reset
+ *(.rodata)
+ *(.rodata.*)
+                0x0800021c                        . = ALIGN (0x4)
+                0x0800021c                        _data_addr = LOADADDR (.data)
+
+.glue_7         0x0800021c        0x0
+ .glue_7        0x0800021c        0x0 linker stubs
+
+.glue_7t        0x0800021c        0x0
+ .glue_7t       0x0800021c        0x0 linker stubs
+
+.vfp11_veneer   0x0800021c        0x0
+ .vfp11_veneer  0x0800021c        0x0 linker stubs
+
+.v4_bx          0x0800021c        0x0
+ .v4_bx         0x0800021c        0x0 linker stubs
+
+.iplt           0x0800021c        0x0
+ .iplt          0x0800021c        0x0 build/startup.o
+
+.rel.dyn        0x0800021c        0x0
+ .rel.iplt      0x0800021c        0x0 build/startup.o
+
+.data           0x20000000        0x0 load address 0x0800021c
+                0x20000000                        . = ALIGN (0x4)
+                0x20000000                        _data_start = .
+ *(.data)
+ *(.data.*)
+                0x20000000                        . = ALIGN (0x4)
+                0x20000000                        _data_end = .
+
+.igot.plt       0x20000000        0x0 load address 0x0800021c
+ .igot.plt      0x20000000        0x0 build/startup.o
+
+.bss            0x20000000        0x0 load address 0x0800021c
+                0x20000000                        . = ALIGN (0x4)
+                0x20000000                        _bss_start = .
+ *(.bss)
+ *(.bss.*)
+                0x20000000                        _bss_end = .
+                0x20000000                        . = ALIGN (0x4)
+OUTPUT(build/final.elf elf32-littlearm)
+LOAD linker stubs
+
+.debug_info     0x00000000      0x1be
+ .debug_info    0x00000000       0x48 build/main.o
+ .debug_info    0x00000048      0x176 build/startup.o
+
+.debug_abbrev   0x00000000      0x14a
+ .debug_abbrev  0x00000000       0x3c build/main.o
+ .debug_abbrev  0x0000003c      0x10e build/startup.o
+
+.debug_aranges  0x00000000       0x48
+ .debug_aranges
+                0x00000000       0x20 build/main.o
+ .debug_aranges
+                0x00000020       0x28 build/startup.o
+
+.debug_rnglists
+                0x00000000       0x2c
+ .debug_rnglists
+                0x00000000       0x13 build/main.o
+ .debug_rnglists
+                0x00000013       0x19 build/startup.o
+
+.debug_macro    0x00000000     0x19f3
+ .debug_macro   0x00000000      0xaaa build/main.o
+ .debug_macro   0x00000aaa      0xafc build/startup.o
+ .debug_macro   0x000015a6       0x22 build/startup.o
+ .debug_macro   0x000015c8       0x8e build/startup.o
+ .debug_macro   0x00001656       0x51 build/startup.o
+ .debug_macro   0x000016a7      0x103 build/startup.o
+ .debug_macro   0x000017aa       0x6a build/startup.o
+ .debug_macro   0x00001814      0x1df build/startup.o
+
+.debug_line     0x00000000      0x120
+ .debug_line    0x00000000       0x4f build/main.o
+ .debug_line    0x0000004f       0xd1 build/startup.o
+
+.debug_str      0x00000000     0x3be8
+ .debug_str     0x00000000     0x2da8 build/main.o
+ .debug_str     0x00002da8      0xe40 build/startup.o
+                               0x3d41 (size before relaxing)
+
+.comment        0x00000000       0x45
+ .comment       0x00000000       0x45 build/main.o
+                                 0x46 (size before relaxing)
+ .comment       0x00000045       0x46 build/startup.o
+
+.ARM.attributes
+                0x00000000       0x34
+ .ARM.attributes
+                0x00000000       0x34 build/main.o
+ .ARM.attributes
+                0x00000034       0x34 build/startup.o
+
+.debug_line_str
+                0x00000000      0x210
+ .debug_line_str
+                0x00000000       0x35 build/main.o
+ .debug_line_str
+                0x00000035      0x1db build/startup.o
+                                0x21b (size before relaxing)
+
+.debug_frame    0x00000000       0x84
+ .debug_frame   0x00000000       0x30 build/main.o
+ .debug_frame   0x00000030       0x54 build/startup.o

link.ld

@@ -0,0 +1,43 @@
+ENTRY(reset);
+
+MEMORY {
+  flash(rx)  : ORIGIN = 0x08000000, LENGTH = 512K
+  sram(rwx) : ORIGIN = 0x20000000, LENGTH = 128K
+}
+stack_start = ORIGIN(sram) + LENGTH(sram); /* stack points to end of sram */
+
+SECTIONS {
+  .isr_vector : {
+    . = ALIGN(4);
+    KEEP(*(.isr_vector))
+    . = ALIGN(4);
+  } > flash
+
+  .text : { /* code and constants */
+    . = ALIGN(4);
+    *(.text)
+    *(.text.*)
+    *(.rodata)
+    *(.rodata.*)
+    . = ALIGN(4);
+  } > flash
+
+  _data_addr = LOADADDR(.data);
+  .data : { /* intialized variables */
+    . = ALIGN(4);
+    _data_start = .;
+    *(.data)
+    *(.data.*)
+    . = ALIGN(4);
+    _data_end = .;
+  } > sram AT > flash /* loads the section into sram, with initial values stored in flash */
+
+  .bss : { /* unintialized variables */
+    . = ALIGN(4);
+    _bss_start = .;
+    *(.bss)
+    *(.bss.*)
+    _bss_end = .;
+    . = ALIGN(4);
+  } > sram
+}

src/startup.c

@@ -0,0 +1,34 @@
+#include <stdint.h>
+
+extern void stack_start(void);  // Defined in link.ld
+extern int main(void);
+
+void init_memory(void) {
+  // Copy .data SECTION to ram
+  extern uint32_t _data_start, _data_end, _data_addr;
+  for (uint32_t *dst = &_data_start, *src = &_data_addr; dst < &_data_end;) {
+	*dst++ = *src++;
+  }
+
+  // Initialize .bss SECTION with zeros
+  extern uint32_t _bss_start, _bss_end;
+  for (uint32_t *dst = &_bss_start; dst < &_bss_end; dst++) {
+	*dst = 0;
+  }
+}
+
+void reset(void) {
+  (void)init_memory();
+
+  main();
+
+  // Infinite loop in case main returns
+  for (;;) (void) 0;
+}
+
+// Create minimal interrupt vector table
+// 16 standard and 86 STM32F411xC/E-specific handlers
+void (*const interrupt_vector_table[16 + 86])(void) __attribute__((section(".isr_vector"))) = {
+  stack_start, // Defined in link.ld
+  reset
+};