Name: Small Common Section Handling
Author: Rusty Russell
Status: Untested

D: Richard Henderson points out that some archs need to make sure that small
D: symbols are within reach of the GOT/GP pointer.  This is part of
D: the solution (the other is to allow archs to reorder sections at load
D: time).

diff -urpN --exclude TAGS -X /home/rusty/devel/kernel/kernel-patches/current-dontdiff --minimal linux-2.5.52/kernel/module.c working-2.5.52-common/kernel/module.c
--- linux-2.5.52/kernel/module.c	2002-12-17 08:11:03.000000000 +1100
+++ working-2.5.52-common/kernel/module.c	2002-12-26 15:25:00.000000000 +1100
@@ -38,6 +38,12 @@
 #define DEBUGP(fmt , a...)
 #endif
 
+/* You must be below this line to be considered small, and hence
+   closest to start of module. */
+#ifndef MODULE_SMALL_COMMON_SIZE
+#define MODULE_SMALL_COMMON_SIZE 0
+#endif
+
 #define symbol_is(literal, string)				\
 	(strcmp(MODULE_SYMBOL_PREFIX literal, (string)) == 0)
 
@@ -834,12 +840,13 @@ static int handle_section(const char *na
 }
 
 /* Figure out total size desired for the common vars */
-static unsigned long read_commons(void *start, Elf_Shdr *sechdr)
+static unsigned long read_commons(void *start, Elf_Shdr *sechdr,
+				  unsigned long *scommon_offset)
 {
-	unsigned long size, i, max_align;
+	unsigned long bsize, ssize, i, max_align;
 	Elf_Sym *sym;
 	
-	size = max_align = 0;
+	size = ssize = max_align = 0;
 
 	for (sym = start + sechdr->sh_offset, i = 0;
 	     i < sechdr->sh_size / sizeof(Elf_Sym);
@@ -848,15 +855,23 @@ static unsigned long read_commons(void *
 			/* Value encodes alignment. */
 			if (sym[i].st_value > max_align)
 				max_align = sym[i].st_value;
-			/* Pad to required alignment */
-			size = ALIGN(size, sym[i].st_value) + sym[i].st_size;
+			
+			if (sym[i].st_size >= MODULE_SMALL_COMMON_SIZE)
+				/* Big section: pad to required alignment */
+				bsize = ALIGN(bsize, sym[i].st_value)
+					+ sym[i].st_size;
+			else /* Small section. */
+				ssize = ALIGN(ssize, sym[i].st_value)
+					+ sym[i].st_size;
 		}
 	}
 
+	*scommon_offset = bsize;
+
 	/* Now, add in max alignment requirement (with align
 	   attribute, this could be large), so we know we have space
 	   whatever the start alignment is */
-	return size + max_align;
+	return bsize + ssize + max_align;
 }
 
 /* Change all symbols so that sh_value encodes the pointer directly. */
@@ -864,6 +879,7 @@ static void simplify_symbols(Elf_Shdr *s
 			     unsigned int symindex,
 			     unsigned int strindex,
 			     void *common,
+			     void *scommon,
 			     struct module *mod)
 {
 	unsigned int i;
@@ -877,14 +893,20 @@ static void simplify_symbols(Elf_Shdr *s
 	     i++) {
 		switch (sym[i].st_shndx) {
 		case SHN_COMMON:
-			/* Value encodes alignment. */
-			common = (void *)ALIGN((unsigned long)common,
-					       sym[i].st_value);
-			/* Change it to encode pointer */
-			sym[i].st_value = (unsigned long)common;
-			common += sym[i].st_size;
+			if (sym[i].st_size >= MODULE_SMALL_COMMON_SIZE) {
+				/* Value encodes alignment. */
+				common = (void *)ALIGN((unsigned long)common,
+						       sym[i].st_value);
+				/* Change it to encode pointer */
+				sym[i].st_value = (unsigned long)common;
+				common += sym[i].st_size;
+			} else {
+				scommon = (void *)ALIGN((unsigned long)scommon,
+							sym[i].st_value);
+				sym[i].st_value = (unsigned long)scommon;
+				scommon += sym[i].st_size;
+			}
 			break;
-
 		case SHN_ABS:
 			/* Don't need to do anything */
 			DEBUGP("Absolute symbol: 0x%08lx\n",
@@ -967,7 +989,7 @@ static struct module *load_module(void *
 	unsigned int i, symindex, exportindex, strindex, setupindex, exindex,
 		modnameindex, obsparmindex;
 	long arglen;
-	unsigned long common_length;
+	unsigned long common_length, scommon_offset;
 	struct sizes sizes, used;
 	struct module *mod;
 	long err = 0;
@@ -1092,7 +1114,7 @@ static struct module *load_module(void *
 	module_unload_init(mod);
 
 	/* How much space will we need?  (Common area in first) */
-	common_length = read_commons(hdr, &sechdrs[symindex]);
+	common_length = read_commons(hdr, &sechdrs[symindex], &scommon_offset);
 	sizes = get_sizes(hdr, sechdrs, secstrings, common_length);
 
 	/* Set these up, and allow archs to manipulate them. */
@@ -1147,7 +1169,8 @@ static struct module *load_module(void *
 		BUG();
 
 	/* Fix up syms, so that st_value is a pointer to location. */
-	simplify_symbols(sechdrs, symindex, strindex, mod->module_core, mod);
+	simplify_symbols(sechdrs, symindex, strindex, mod->module_core,
+			 mod->module_core + scommon_offset, mod);
 
 	/* Set up EXPORTed symbols */
 	if (exportindex) {