diff --git a/ports/analog/Makefile b/ports/analog/Makefile
index 6b86bd70396..c81280e11ab 100644
--- a/ports/analog/Makefile
+++ b/ports/analog/Makefile
@@ -299,7 +299,7 @@ $(BUILD)/firmware.elf: $(OBJ)
 	$(STEPECHO) "LINK $@"
 	$(Q)echo $^ > $(BUILD)/firmware.objs
 	$(Q)$(CC) -o $@ $(LDFLAGS) @$(BUILD)/firmware.objs -Wl,--print-memory-usage -Wl,--start-group $(LIBS) -Wl,--end-group
-	$(Q)$(SIZE) $@ | $(PYTHON) $(TOP)/tools/build_memory_info.py $(LINKERFILE) $(BUILD)
+	$(Q)$(SIZE) $@ | $(PYTHON) $(TOP)/tools/build_memory_info.py $@.map $(BUILD)
 
 $(BUILD)/firmware.hex: $(BUILD)/firmware.elf
 	$(STEPECHO) "Create $@"
diff --git a/ports/atmel-samd/Makefile b/ports/atmel-samd/Makefile
index 0aaf6e3d849..ad4e65b6ddb 100644
--- a/ports/atmel-samd/Makefile
+++ b/ports/atmel-samd/Makefile
@@ -348,7 +348,7 @@ $(BUILD)/firmware.elf: $(OBJ) $(GENERATED_LD_FILE)
 	$(STEPECHO) "LINK $@"
 	$(Q)echo $(OBJ) > $(BUILD)/firmware.objs
 	$(Q)$(CC) -o $@ $(LDFLAGS) @$(BUILD)/firmware.objs -Wl,--print-memory-usage -Wl,--start-group $(LIBS) -Wl,--end-group
-	$(Q)$(SIZE) $@ | $(PYTHON) $(TOP)/tools/build_memory_info.py $(GENERATED_LD_FILE) $(BUILD)
+	$(Q)$(SIZE) $@ | $(PYTHON) $(TOP)/tools/build_memory_info.py $@.map $(BUILD)
 endif
 
 $(BUILD)/firmware.bin: $(BUILD)/firmware.elf
diff --git a/ports/litex/Makefile b/ports/litex/Makefile
index cc813a49f8e..9792ce301a3 100644
--- a/ports/litex/Makefile
+++ b/ports/litex/Makefile
@@ -118,7 +118,7 @@ else
 $(BUILD)/firmware.elf: $(OBJ)
 	$(STEPECHO) "LINK $@"
 	$(Q)$(CC) -o $@ $(LDFLAGS) $^ -Wl,--print-memory-usage -Wl,--start-group $(LIBS) -Wl,--end-group
-	$(Q)$(SIZE) $@ | $(PYTHON) $(TOP)/tools/build_memory_info.py $(LD_FILE) $(BUILD)
+	$(Q)$(SIZE) $@ | $(PYTHON) $(TOP)/tools/build_memory_info.py $@.map $(BUILD)
 endif
 
 $(BUILD)/firmware.bin: $(BUILD)/firmware.elf
diff --git a/ports/mimxrt10xx/Makefile b/ports/mimxrt10xx/Makefile
index 74667fd3d64..95fedc70d8e 100644
--- a/ports/mimxrt10xx/Makefile
+++ b/ports/mimxrt10xx/Makefile
@@ -189,6 +189,7 @@ else
 $(BUILD)/firmware.elf: $(OBJ) $(LD_FILES)
 	$(STEPECHO) "LINK $@"
 	$(Q)$(CC) -o $@ $(LDFLAGS) $(filter-out %.ld, $^) -Wl,--print-memory-usage -Wl,--start-group $(LIBS) -Wl,--end-group
+	$(Q)$(SIZE) $@ | $(PYTHON) $(TOP)/tools/build_memory_info.py $@.map $(BUILD)
 endif
 
 # -R excludes sections from the output files.
diff --git a/ports/nordic/Makefile b/ports/nordic/Makefile
index ec755fac892..2abee97386c 100755
--- a/ports/nordic/Makefile
+++ b/ports/nordic/Makefile
@@ -200,7 +200,7 @@ $(BUILD)/firmware.elf: $(OBJ) $(GENERATED_LD_FILE)
 	$(STEPECHO) "LINK $@"
 	$(Q)echo $(OBJ) > $(BUILD)/firmware.objs
 	$(Q)$(CC) -o $@ $(LDFLAGS) @$(BUILD)/firmware.objs -Wl,--print-memory-usage -Wl,--start-group $(LIBS) -Wl,--end-group
-	$(Q)$(SIZE) $@ | $(PYTHON) $(TOP)/tools/build_memory_info.py $(GENERATED_LD_FILE) $(BUILD)
+	$(Q)$(SIZE) $@ | $(PYTHON) $(TOP)/tools/build_memory_info.py $@.map $(BUILD)
 endif
 
 $(BUILD)/firmware.bin: $(BUILD)/firmware.elf
diff --git a/ports/raspberrypi/Makefile b/ports/raspberrypi/Makefile
index 1c13d538e51..5512c7c9f47 100755
--- a/ports/raspberrypi/Makefile
+++ b/ports/raspberrypi/Makefile
@@ -834,6 +834,7 @@ $(BUILD)/firmware.elf: $(OBJ) $(BOARD_LD) link-$(CHIP_VARIANT_LOWER).ld
 	$(Q)echo $(OBJ) > $(BUILD)/firmware.objs
 	$(Q)echo $(PICO_LDFLAGS) > $(BUILD)/firmware.ldflags
 	$(Q)$(CC) -o $@ $(CFLAGS) @$(BUILD)/firmware.ldflags $(LINKER_SCRIPTS) -Wl,--print-memory-usage -Wl,-Map=$@.map -Wl,-cref -Wl,--gc-sections @$(BUILD)/firmware.objs -Wl,-lc
+	$(Q)$(SIZE) $@ | $(PYTHON) $(TOP)/tools/build_memory_info.py $@.map $(BUILD)
 ifneq ($(CORE1_CHECK_ROOTS),)
 	$(STEPECHO) "CHECK core1 flash calls"
 	$(Q)$(PYTHON) $(TOP)/tools/check_core1_flash_calls.py $@ $(CORE1_CHECK_ROOTS)
diff --git a/ports/renode/Makefile b/ports/renode/Makefile
index c4ce66194e9..b69d8d251ef 100644
--- a/ports/renode/Makefile
+++ b/ports/renode/Makefile
@@ -88,6 +88,7 @@ $(BUILD)/firmware.elf: $(OBJ) $(BOARD_LD) link.ld
 	$(Q)echo $(OBJ) > $(BUILD)/firmware.objs
 	$(Q)echo $(PICO_LDFLAGS) > $(BUILD)/firmware.ldflags
 	$(Q)$(CC) -o $@ $(CFLAGS) @$(BUILD)/firmware.ldflags $(LINKER_SCRIPTS) -Wl,--print-memory-usage -Wl,-Map=$@.map -Wl,-cref -Wl,--gc-sections @$(BUILD)/firmware.objs -Wl,-lc
+	$(Q)$(SIZE) $@ | $(PYTHON) $(TOP)/tools/build_memory_info.py $@.map $(BUILD)
 endif
 
 $(BUILD)/firmware.bin: $(BUILD)/firmware.elf
diff --git a/ports/silabs/Makefile b/ports/silabs/Makefile
index 810ab53f1f3..5c0f01e86b1 100644
--- a/ports/silabs/Makefile
+++ b/ports/silabs/Makefile
@@ -134,7 +134,8 @@ $(SILABS_BUILD)/$(PROJECTNAME).Makefile: | $(HEADER_BUILD)/mpversion.h
 $(OUTPUT_DIR)/firmware.out: $(SILABS_BUILD)/pin_functions.h $(SILABS_BUILD)/pins.c $(OBJ) $(OBJS) $(LIB_FILES)
 	$(STEPECHO) 'Linking $(OUTPUT_DIR)/firmware.out'
 	$(Q)echo "$(OBJS) $(OBJ)" > $(OUTPUT_DIR)/linker_objs
-	$(Q)$(CC) $(LD_FLAGS) @$(OUTPUT_DIR)/linker_objs -Wl,--print-memory-usage $(LIBS) -o $(OUTPUT_DIR)/firmware.out
+	$(Q)$(CC) $(LD_FLAGS) @$(OUTPUT_DIR)/linker_objs -Wl,--print-memory-usage -Wl,-Map=$(OUTPUT_DIR)/firmware.out.map $(LIBS) -o $(OUTPUT_DIR)/firmware.out
+	$(Q)$(SIZE) $(OUTPUT_DIR)/firmware.out | $(PYTHON) $(TOP)/tools/build_memory_info.py $(OUTPUT_DIR)/firmware.out.map $(BUILD)
 	$(Q)$(OBJCOPY) $(OUTPUT_DIR)/firmware.out -O binary $(OUTPUT_DIR)/firmware.bin
 
 flash: $(OUTPUT_DIR)/firmware.bin
diff --git a/ports/stm/Makefile b/ports/stm/Makefile
index 5ad0c82654c..f7c17ea8d42 100755
--- a/ports/stm/Makefile
+++ b/ports/stm/Makefile
@@ -257,7 +257,7 @@ $(BUILD)/firmware.elf: $(OBJ)
 	$(STEPECHO) "LINK $@"
 	$(Q)echo $^ > $(BUILD)/firmware.objs
 	$(Q)$(CC) -o $@ $(LDFLAGS) @$(BUILD)/firmware.objs -Wl,--print-memory-usage -Wl,--start-group $(LIBS) -Wl,--end-group
-	$(Q)$(SIZE) $@ | $(PYTHON) $(TOP)/tools/build_memory_info.py $(LD_FILE) $(BUILD)
+	$(Q)$(SIZE) $@ | $(PYTHON) $(TOP)/tools/build_memory_info.py $@.map $(BUILD)
 endif
 
 $(BUILD)/firmware.bin: $(BUILD)/firmware.elf
diff --git a/ports/zephyr-cp/Makefile b/ports/zephyr-cp/Makefile
index fbde791afa9..e21a96e9eb8 100644
--- a/ports/zephyr-cp/Makefile
+++ b/ports/zephyr-cp/Makefile
@@ -52,6 +52,7 @@ export BSIM_OUT_PATH := $(CURDIR)/tools/bsim
 $(BUILD)/zephyr-cp/zephyr/zephyr.elf:
 	python cptools/pre_zephyr_build_prep.py $(BOARD)
 	west build -b $(BOARD) -d $(BUILD) $(WEST_SHIELD_ARGS) --sysbuild -- $(WEST_CMAKE_ARGS)
+	python ../../tools/build_memory_info.py $(BUILD)/zephyr-cp/zephyr/zephyr.map $(BUILD) --image $(BUILD)/zephyr-cp/zephyr/zephyr.bin
 
 $(BUILD)/firmware.elf: $(BUILD)/zephyr-cp/zephyr/zephyr.elf
 	cp $^ $@
diff --git a/tools/build_memory_info.py b/tools/build_memory_info.py
index ff5bbfad710..8e24cbc709e 100755
--- a/tools/build_memory_info.py
+++ b/tools/build_memory_info.py
@@ -5,55 +5,105 @@
 #
 # SPDX-License-Identifier: MIT
 
+import os
 import re
 import sys
 import json
 
 
-# Handle size constants with K or M suffixes (allowed in .ld but not in Python).
-K_PATTERN = re.compile(r"([0-9]+)[kK]")
-K_REPLACE = r"(\1*1024)"
+# A linker map lists every region with the lengths already resolved:
+#     Name             Origin             Length             Attributes
+#     FLASH_FIRMWARE   0x10000000         0x0017f000         xr
+MAP_REGION = re.compile(r"^(\w+)\s+0x[0-9a-f]+\s+0x([0-9a-f]+)\s+\S*$", re.MULTILINE)
 
-M_PATTERN = re.compile(r"([0-9]+)[mM]")
-M_REPLACE = r"(\1*1024*1024)"
+argv = sys.argv[1:]
+flash_names = ["FLASH_FIRMWARE", "FLASH"]
+if "--region" in argv:
+    i = argv.index("--region")
+    flash_names = argv[i + 1].split(",")
+    del argv[i : i + 2]
+
+# Ports whose toolchain this makefile cannot reach pass the image instead of piping
+# size(1) in; what it occupies in flash is its size on disk.
+image = None
+if "--image" in argv:
+    i = argv.index("--image")
+    image = argv[i + 1]
+    del argv[i : i + 2]
 
 text = 0
 data = 0
 bss = 0
 
-# stdin is the linker output.
-for line in sys.stdin:
-    # Uncomment to see linker output.
-    # print(line)
-    line = line.strip()
-    if not line.startswith("text"):
-        text, data, bss = map(int, line.split()[:3])
+if image is None:
+    # stdin is the linker output.
+    for line in sys.stdin:
+        # Uncomment to see linker output.
+        # print(line)
+        line = line.strip()
+        if not line.startswith("text"):
+            text, data, bss = map(int, line.split()[:3])
 
-regions = {}
 
-# This file is the linker script.
-with open(sys.argv[1], "r") as f:
-    for line in f:
-        line = line.strip()
-        if line.startswith(("FLASH_FIRMWARE", "RAM")):
-            regions[line.split()[0]] = line.split("=")[-1]
+def regions_from_map(contents):
+    """Region sizes from the Memory Configuration table of a linker map."""
+    start = contents.find("Memory Configuration")
+    if start < 0:
+        return None
+    end = contents.find("Linker script and memory map", start)
+    table = contents[start : end if end > 0 else len(contents)]
+    regions = {}
+    for name, length in MAP_REGION.findall(table):
+        if name not in ("Name", "Origin", "Length"):
+            regions[name] = int(length, 16)
+    return regions or None
 
-for region, space in regions.items():
-    if "/*" in space:
-        space = space.split("/*")[0]
-    space = K_PATTERN.sub(K_REPLACE, space)
-    space = M_PATTERN.sub(M_REPLACE, space)
-    regions[region] = int(eval(space))
 
-firmware_region = regions["FLASH_FIRMWARE"]
-ram_region = regions["RAM"]
+# The linker map lists the regions with every size the script computed resolved.
+try:
+    with open(argv[0], "r") as f:
+        contents = f.read()
+except FileNotFoundError:
+    print()
+    print(f"No {argv[0]} to read the flash region from.")
+    print()
+    sys.exit(0)
+regions = regions_from_map(contents) or {}
+
+firmware_region = None
+for name in flash_names:
+    if name in regions:
+        firmware_region = regions[name]
+        break
+
+if image is not None:
+    try:
+        text = os.stat(image).st_size
+    except FileNotFoundError:
+        print()
+        print(f"No {image} to measure.")
+        print()
+        sys.exit(0)
 
 used_flash = data + text
-free_flash = firmware_region - used_flash
 used_ram = data + bss
-free_ram = ram_region - used_ram
 
-with open(f"{sys.argv[2]}/firmware.size.json", "w") as f:
+if firmware_region is None:
+    # Not knowing the size is not worth failing a build over: the tools that read
+    # firmware.size.json fall back to assuming there is no headroom.
+    print()
+    print(
+        "No {} region in {}. Regions found: {}.".format(
+            " or ".join(flash_names), argv[0], ", ".join(sorted(regions)) or "none"
+        )
+    )
+    print("{} bytes used in flash firmware space.".format(used_flash))
+    print()
+    sys.exit(0)
+
+free_flash = firmware_region - used_flash
+
+with open(f"{argv[1]}/firmware.size.json", "w") as f:
     json.dump({"used_flash": used_flash, "firmware_region": firmware_region}, f)
 
 print()
@@ -62,16 +112,11 @@
         used_flash, free_flash, firmware_region, firmware_region / 1024
     )
 )
-print(
-    "{} bytes used, {} bytes free in ram for stack and heap out of {} bytes ({}kB).".format(
-        used_ram, free_ram, ram_region, ram_region / 1024
+if image is None and "RAM" in regions:
+    ram_region = regions["RAM"]
+    print(
+        "{} bytes used, {} bytes free in ram for stack and heap out of {} bytes ({}kB).".format(
+            used_ram, ram_region - used_ram, ram_region, ram_region / 1024
+        )
     )
-)
 print()
-
-# Check that we have free flash space. GCC doesn't fail when the text + data
-# sections don't fit in FLASH. It only counts data in RAM.
-if free_flash < 0:
-    print("Too little flash!!!")
-    print()
-    sys.exit(-1)