Force a link error if a function is used from the wrong code chunk.

Force functions intended for other code segments to be discarded
    during link - this will cause a link error if it used.
Clean up rom layout code to ensure discarded sections are not used.

2 files changed, 31 insertions, 24 deletions

diff --git a/src/types.h b/src/types.h
index b2100c1..59999c5 100644
--- a/src/types.h
+++ b/src/types.h
@@ -35,6 +35,7 @@ union u64_u32_u {
 
 #define __noreturn __attribute__((noreturn))
 extern void __force_link_error__only_in_32bit_flat() __noreturn;
+extern void __force_link_error__only_in_32bit_segmented() __noreturn;
 extern void __force_link_error__only_in_16bit() __noreturn;
 
 #define __ASM(code) asm(".section .text.asm." UNIQSEC "\n\t" code)
@@ -43,9 +44,9 @@ extern void __force_link_error__only_in_16bit() __noreturn;
 // Notes a function as externally visible in the 16bit code chunk.
 # define VISIBLE16 __VISIBLE
 // Notes a function as externally visible in the 32bit flat code chunk.
-# define VISIBLE32FLAT
+# define VISIBLE32FLAT __section(".discard.func32flat." UNIQSEC) noinline
 // Notes a function as externally visible in the 32bit segmented code chunk.
-# define VISIBLE32SEG
+# define VISIBLE32SEG __section(".discard.func32seg." UNIQSEC) noinline
 // Designate a variable as (only) visible to 16bit code.
 # define VAR16 __section(".data16." UNIQSEC)
 // Designate a variable as visible to 16bit, 32bit, and assembler code.
@@ -63,11 +64,12 @@ extern void __force_link_error__only_in_16bit() __noreturn;
 // Designate top-level assembler as 32bit flat only.
 # define ASM32FLAT(code)
 // Compile time check for a given mode.
-#define ASSERT16() do { } while (0)
-#define ASSERT32FLAT() __force_link_error__only_in_32bit_flat()
+# define ASSERT16() do { } while (0)
+# define ASSERT32SEG() __force_link_error__only_in_32bit_segmented()
+# define ASSERT32FLAT() __force_link_error__only_in_32bit_flat()
 #elif MODESEGMENT == 1
-# define VISIBLE16
-# define VISIBLE32FLAT
+# define VISIBLE16 __section(".discard.func16." UNIQSEC) noinline
+# define VISIBLE32FLAT __section(".discard.func32flat." UNIQSEC) noinline
 # define VISIBLE32SEG __VISIBLE
 # define VAR16 __section(".discard.var16." UNIQSEC)
 # define VAR16VISIBLE VAR16 __VISIBLE __weak
@@ -77,12 +79,13 @@ extern void __force_link_error__only_in_16bit() __noreturn;
 # define VAR32FLATVISIBLE __section(".discard.var32flat." UNIQSEC) __VISIBLE __weak
 # define ASM16(code)
 # define ASM32FLAT(code)
-#define ASSERT16() __force_link_error__only_in_16bit()
-#define ASSERT32FLAT() __force_link_error__only_in_32bit_flat()
+# define ASSERT16() __force_link_error__only_in_16bit()
+# define ASSERT32SEG() do { } while (0)
+# define ASSERT32FLAT() __force_link_error__only_in_32bit_flat()
 #else
-# define VISIBLE16
+# define VISIBLE16 __section(".discard.func16." UNIQSEC) noinline
 # define VISIBLE32FLAT __VISIBLE
-# define VISIBLE32SEG
+# define VISIBLE32SEG __section(".discard.func32seg." UNIQSEC) noinline
 # define VAR16 __section(".discard.var16." UNIQSEC)
 # define VAR16VISIBLE VAR16 __VISIBLE __weak
 # define VAR16EXPORT VAR16VISIBLE
@@ -91,8 +94,9 @@ extern void __force_link_error__only_in_16bit() __noreturn;
 # define VAR32FLATVISIBLE __VISIBLE
 # define ASM16(code)
 # define ASM32FLAT(code) __ASM(code)
-#define ASSERT16() __force_link_error__only_in_16bit()
-#define ASSERT32FLAT() do { } while (0)
+# define ASSERT16() __force_link_error__only_in_16bit()
+# define ASSERT32SEG() __force_link_error__only_in_32bit_segmented()
+# define ASSERT32FLAT() do { } while (0)
 #endif
 
 #define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)
diff --git a/tools/layoutrom.py b/tools/layoutrom.py
index 3113407..d0ca9a6 100755
--- a/tools/layoutrom.py
+++ b/tools/layoutrom.py
@@ -274,6 +274,14 @@ def getSectionsList(info, names):
         out.append(i)
     return out
 
+# Find and keep the section associated with a symbol (if available).
+def keepsymbol(symbol, infos, pos):
+    addr, section = infos[pos][1].get(symbol, (None, None))
+    if section is None or '*' in section or section[:9] == '.discard.':
+        return -1
+    keepsection(section, infos, pos)
+    return 0
+
 # Note required section, and recursively set all referenced sections
 # as required.
 def keepsection(name, infos, pos=0):
@@ -286,21 +294,16 @@ def keepsection(name, infos, pos=0):
         return
     # Keep all sections that this section points to
     for symbol in relocs:
-        addr, section = infos[pos][1].get(symbol, (None, None))
-        if (section is not None and '*' not in section
-            and section[:9] != '.discard.'):
-            keepsection(section, infos, pos)
+        ret = keepsymbol(symbol, infos, pos)
+        if not ret:
             continue
         # Not in primary sections - it may be a cross 16/32 reference
-        newpos = (pos+1)%3
-        addr, section = infos[newpos][1].get(symbol, (None, None))
-        if section is not None and '*' not in section:
-            keepsection(section, infos, newpos)
+        ret = keepsymbol(symbol, infos, (pos+1)%3)
+        if not ret:
+            continue
+        ret = keepsymbol(symbol, infos, (pos+2)%3)
+        if not ret:
             continue
-        newpos = (pos+2)%3
-        addr, section = infos[(pos+2)%3][1].get(symbol, (None, None))
-        if section is not None and '*' not in section:
-            keepsection(section, infos, newpos)
 
 # Determine which sections are actually referenced and need to be
 # placed into the output file.