parisc: fix module loading failure of large kernel modules

On 32bit (and sometimes 64bit) and with big kernel modules like xfs or
ipv6 the relocation types R_PARISC_PCREL17F and R_PARISC_PCREL22F may
fail to reach their PLT stub if we only create one big stub array for
all sections at the beginning of the core or init section.

With this patch we now instead add individual PLT stub entries
directly in front of the code sections where the stubs are actually
called. This reduces the distance between the PCREL location and the
stub entry so that the relocations can be fulfilled.

While calculating the final layout of the kernel module in memory, the
kernel module loader calls arch_mod_section_prepend() to request the
to be reserved amount of memory in front of each individual section.

Tested with 32- and 64bit kernels.

Signed-off-by: Helge Deller <[e-mail]>
Signed-off-by: Rusty Russell <[e-mail]>

arch/parisc/include/asm/module.h

···
 {
 	unsigned long got_offset, got_count, got_max;
 	unsigned long fdesc_offset, fdesc_count, fdesc_max;
-	unsigned long stub_offset, stub_count, stub_max;
-	unsigned long init_stub_offset, init_stub_count, init_stub_max;
+	struct {
+		unsigned long stub_offset;
+		unsigned int stub_entries;
+		} *section;
 	int unwind_section;
 	struct unwind_table *unwind;
 };

arch/parisc/kernel/module.c

···
  *
  *    Linux/PA-RISC Project (http://www.parisc-linux.org/)
  *    Copyright (C) 2003 Randolph Chung <tausq at debian . org>
+ *    Copyright (C) 2008 Helge Deller <[e-mail]>
  *
  *
  *    This program is free software; you can redistribute it and/or modify
···
  *
  *
  *    Notes:
+ *    - PLT stub handling
+ *      On 32bit (and sometimes 64bit) and with big kernel modules like xfs or
+ *      ipv6 the relocation types R_PARISC_PCREL17F and R_PARISC_PCREL22F may
+ *      fail to reach their PLT stub if we only create one big stub array for
+ *      all sections at the beginning of the core or init section.
+ *      Instead we now insert individual PLT stub entries directly in front of
+ *      of the code sections where the stubs are actually called.
+ *      This reduces the distance between the PCREL location and the stub entry
+ *      so that the relocations can be fulfilled.
+ *      While calculating the final layout of the kernel module in memory, the
+ *      kernel module loader calls arch_mod_section_prepend() to request the
+ *      to be reserved amount of memory in front of each individual section.
+ *
  *    - SEGREL32 handling
  *      We are not doing SEGREL32 handling correctly. According to the ABI, we
  *      should do a value offset, like this:
···
 #define DEBUGP(fmt...)
 #endif
 
+#define RELOC_REACHABLE(val, bits) \
+	(( ( !((val) & (1<<((bits)-1))) && ((val)>>(bits)) != 0 )  ||	\
+	     ( ((val) & (1<<((bits)-1))) && ((val)>>(bits)) != (((__typeof__(val))(~0))>>((bits)+2)))) ? \
+	0 : 1)
+
 #define CHECK_RELOC(val, bits) \
-	if ( ( !((val) & (1<<((bits)-1))) && ((val)>>(bits)) != 0 )  ||	\
-	     ( ((val) & (1<<((bits)-1))) && ((val)>>(bits)) != (((__typeof__(val))(~0))>>((bits)+2)))) { \
+	if (!RELOC_REACHABLE(val, bits)) { \
 		printk(KERN_ERR "module %s relocation of symbol %s is out of range (0x%lx in %d bits)\n", \
 		me->name, strtab + sym->st_name, (unsigned long)val, bits); \
 		return -ENOEXEC;			\
···
 {
 	return in_init(me, loc) || in_core(me, loc);
 }
-
-static inline int in_local_section(struct module *me, void *loc, void *dot)
-{
-	return (in_init(me, loc) && in_init(me, dot)) ||
-		(in_core(me, loc) && in_core(me, dot));
-}
-
 
 #ifndef CONFIG_64BIT
 struct got_entry {
···
 /* Free memory returned from module_alloc */
 void module_free(struct module *mod, void *module_region)
 {
+	kfree(mod->arch.section);
+	mod->arch.section = NULL;
+
 	vfree(module_region);
 	/* FIXME: If module_region == mod->init_region, trim exception
            table entries. */
+}
+
+/* Additional bytes needed in front of individual sections */
+unsigned int arch_mod_section_prepend(struct module *mod,
+				      unsigned int section)
+{
+	/* size needed for all stubs of this section (including
+	 * one additional for correct alignment of the stubs) */
+	return (mod->arch.section[section].stub_entries + 1)
+		* sizeof(struct stub_entry);
 }
 
 #define CONST 
···
 			      CONST char *secstrings,
 			      struct module *me)
 {
-	unsigned long gots = 0, fdescs = 0, stubs = 0, init_stubs = 0;
+	unsigned long gots = 0, fdescs = 0, len;
 	unsigned int i;
 
+	len = hdr->e_shnum * sizeof(me->arch.section[0]);
+	me->arch.section = kzalloc(len, GFP_KERNEL);
+	if (!me->arch.section)
+		return -ENOMEM;
+
 	for (i = 1; i < hdr->e_shnum; i++) {
-		const Elf_Rela *rels = (void *)hdr + sechdrs[i].sh_offset;
+		const Elf_Rela *rels = (void *)sechdrs[i].sh_addr;
 		unsigned long nrels = sechdrs[i].sh_size / sizeof(*rels);
+		unsigned int count, s;
 
 		if (strncmp(secstrings + sechdrs[i].sh_name,
 			    ".PARISC.unwind", 14) == 0)
···
 		 */
 		gots += count_gots(rels, nrels);
 		fdescs += count_fdescs(rels, nrels);
-		if(strncmp(secstrings + sechdrs[i].sh_name,
-			   ".rela.init", 10) == 0)
-			init_stubs += count_stubs(rels, nrels);
-		else
-			stubs += count_stubs(rels, nrels);
+
+		/* XXX: By sorting the relocs and finding duplicate entries
+		 *  we could reduce the number of necessary stubs and save
+		 *  some memory. */
+		count = count_stubs(rels, nrels);
+		if (!count)
+			continue;
+
+		/* so we need relocation stubs. reserve necessary memory. */
+		/* sh_info gives the section for which we need to add stubs. */
+		s = sechdrs[i].sh_info;
+
+		/* each code section should only have one relocation section */
+		WARN_ON(me->arch.section[s].stub_entries);
+
+		/* store number of stubs we need for this section */
+		me->arch.section[s].stub_entries += count;
 	}
 
 	/* align things a bit */
···
 	me->arch.fdesc_offset = me->core_size;
 	me->core_size += fdescs * sizeof(Elf_Fdesc);
 
-	me->core_size = ALIGN(me->core_size, 16);
-	me->arch.stub_offset = me->core_size;
-	me->core_size += stubs * sizeof(struct stub_entry);
-
-	me->init_size = ALIGN(me->init_size, 16);
-	me->arch.init_stub_offset = me->init_size;
-	me->init_size += init_stubs * sizeof(struct stub_entry);
-
 	me->arch.got_max = gots;
 	me->arch.fdesc_max = fdescs;
-	me->arch.stub_max = stubs;
-	me->arch.init_stub_max = init_stubs;
 
 	return 0;
 }
···
 };
 
 static Elf_Addr get_stub(struct module *me, unsigned long value, long addend,
-	enum elf_stub_type stub_type, int init_section)
+	enum elf_stub_type stub_type, Elf_Addr loc0, unsigned int targetsec)
 {
-	unsigned long i;
 	struct stub_entry *stub;
 
-	if(init_section) {
-		i = me->arch.init_stub_count++;
-		BUG_ON(me->arch.init_stub_count > me->arch.init_stub_max);
-		stub = me->module_init + me->arch.init_stub_offset + 
-			i * sizeof(struct stub_entry);
-	} else {
-		i = me->arch.stub_count++;
-		BUG_ON(me->arch.stub_count > me->arch.stub_max);
-		stub = me->module_core + me->arch.stub_offset + 
-			i * sizeof(struct stub_entry);
+	/* initialize stub_offset to point in front of the section */
+	if (!me->arch.section[targetsec].stub_offset) {
+		loc0 -= (me->arch.section[targetsec].stub_entries + 1) *
+				sizeof(struct stub_entry);
+		/* get correct alignment for the stubs */
+		loc0 = ALIGN(loc0, sizeof(struct stub_entry));
+		me->arch.section[targetsec].stub_offset = loc0;
 	}
+
+	/* get address of stub entry */
+	stub = (void *) me->arch.section[targetsec].stub_offset;
+	me->arch.section[targetsec].stub_offset += sizeof(struct stub_entry);
+
+	/* do not write outside available stub area */
+	BUG_ON(0 == me->arch.section[targetsec].stub_entries--);
+
 
 #ifndef CONFIG_64BIT
 /* for 32-bit the stub looks like this:
···
 	Elf32_Addr val;
 	Elf32_Sword addend;
 	Elf32_Addr dot;
+	Elf_Addr loc0;
+	unsigned int targetsec = sechdrs[relsec].sh_info;
 	//unsigned long dp = (unsigned long)$global$;
 	register unsigned long dp asm ("r27");
 
 	DEBUGP("Applying relocate section %u to %u\n", relsec,
-	       sechdrs[relsec].sh_info);
+	       targetsec);
 	for (i = 0; i < sechdrs[relsec].sh_size / sizeof(*rel); i++) {
 		/* This is where to make the change */
-		loc = (void *)sechdrs[sechdrs[relsec].sh_info].sh_addr
+		loc = (void *)sechdrs[targetsec].sh_addr
 		      + rel[i].r_offset;
+		/* This is the start of the target section */
+		loc0 = sechdrs[targetsec].sh_addr;
 		/* This is the symbol it is referring to */
 		sym = (Elf32_Sym *)sechdrs[symindex].sh_addr
 			+ ELF32_R_SYM(rel[i].r_info);
···
 			break;
 		case R_PARISC_PCREL17F:
 			/* 17-bit PC relative address */
-			val = get_stub(me, val, addend, ELF_STUB_GOT, in_init(me, loc));
+			/* calculate direct call offset */
+			val += addend;
 			val = (val - dot - 8)/4;
-			CHECK_RELOC(val, 17)
+			if (!RELOC_REACHABLE(val, 17)) {
+				/* direct distance too far, create
+				 * stub entry instead */
+				val = get_stub(me, sym->st_value, addend,
+					ELF_STUB_DIRECT, loc0, targetsec);
+				val = (val - dot - 8)/4;
+				CHECK_RELOC(val, 17);
+			}
 			*loc = (*loc & ~0x1f1ffd) | reassemble_17(val);
 			break;
 		case R_PARISC_PCREL22F:
 			/* 22-bit PC relative address; only defined for pa20 */
-			val = get_stub(me, val, addend, ELF_STUB_GOT, in_init(me, loc));
-			DEBUGP("STUB FOR %s loc %lx+%lx at %lx\n", 
-			       strtab + sym->st_name, (unsigned long)loc, addend, 
-			       val)
+			/* calculate direct call offset */
+			val += addend;
 			val = (val - dot - 8)/4;
-			CHECK_RELOC(val, 22);
+			if (!RELOC_REACHABLE(val, 22)) {
+				/* direct distance too far, create
+				 * stub entry instead */
+				val = get_stub(me, sym->st_value, addend,
+					ELF_STUB_DIRECT, loc0, targetsec);
+				val = (val - dot - 8)/4;
+				CHECK_RELOC(val, 22);
+			}
 			*loc = (*loc & ~0x3ff1ffd) | reassemble_22(val);
 			break;
 
···
 	Elf64_Addr val;
 	Elf64_Sxword addend;
 	Elf64_Addr dot;
+	Elf_Addr loc0;
+	unsigned int targetsec = sechdrs[relsec].sh_info;
 
 	DEBUGP("Applying relocate section %u to %u\n", relsec,
-	       sechdrs[relsec].sh_info);
+	       targetsec);
 	for (i = 0; i < sechdrs[relsec].sh_size / sizeof(*rel); i++) {
 		/* This is where to make the change */
-		loc = (void *)sechdrs[sechdrs[relsec].sh_info].sh_addr
+		loc = (void *)sechdrs[targetsec].sh_addr
 		      + rel[i].r_offset;
+		/* This is the start of the target section */
+		loc0 = sechdrs[targetsec].sh_addr;
 		/* This is the symbol it is referring to */
 		sym = (Elf64_Sym *)sechdrs[symindex].sh_addr
 			+ ELF64_R_SYM(rel[i].r_info);
···
 			DEBUGP("PCREL22F Symbol %s loc %p val %lx\n",
 			       strtab + sym->st_name,
 			       loc, val);
+			val += addend;
 			/* can we reach it locally? */
-			if(!in_local_section(me, (void *)val, (void *)dot)) {
-
-				if (in_local(me, (void *)val))
-					/* this is the case where the
-					 * symbol is local to the
-					 * module, but in a different
-					 * section, so stub the jump
-					 * in case it's more than 22
-					 * bits away */
-					val = get_stub(me, val, addend, ELF_STUB_DIRECT,
-						       in_init(me, loc));
-				else if (strncmp(strtab + sym->st_name, "$$", 2)
+			if (in_local(me, (void *)val)) {
+				/* this is the case where the symbol is local
+				 * to the module, but in a different section,
+				 * so stub the jump in case it's more than 22
+				 * bits away */
+				val = (val - dot - 8)/4;
+				if (!RELOC_REACHABLE(val, 22)) {
+					/* direct distance too far, create
+					 * stub entry instead */
+					val = get_stub(me, sym->st_value,
+						addend, ELF_STUB_DIRECT,
+						loc0, targetsec);
+				} else {
+					/* Ok, we can reach it directly. */
+					val = sym->st_value;
+					val += addend;
+				}
+			} else {
+				val = sym->st_value;
+				if (strncmp(strtab + sym->st_name, "$$", 2)
 				    == 0)
 					val = get_stub(me, val, addend, ELF_STUB_MILLI,
-						       in_init(me, loc));
+						       loc0, targetsec);
 				else
 					val = get_stub(me, val, addend, ELF_STUB_GOT,
-						       in_init(me, loc));
+						       loc0, targetsec);
 			}
 			DEBUGP("STUB FOR %s loc %lx, val %lx+%lx at %lx\n", 
 			       strtab + sym->st_name, loc, sym->st_value,
 			       addend, val);
-			/* FIXME: local symbols work as long as the
-			 * core and init pieces aren't separated too
-			 * far.  If this is ever broken, you will trip
-			 * the check below.  The way to fix it would
-			 * be to generate local stubs to go between init
-			 * and core */
-			if((Elf64_Sxword)(val - dot - 8) > 0x800000 -1 ||
-			   (Elf64_Sxword)(val - dot - 8) < -0x800000) {
-				printk(KERN_ERR "Module %s, symbol %s is out of range for PCREL22F relocation\n",
-				       me->name, strtab + sym->st_name);
-				return -ENOEXEC;
-			}
 			val = (val - dot - 8)/4;
+			CHECK_RELOC(val, 22);
 			*loc = (*loc & ~0x3ff1ffd) | reassemble_22(val);
 			break;
 		case R_PARISC_DIR64:
···
 	addr = (u32 *)entry->addr;
 	printk("INSNS: %x %x %x %x\n",
 	       addr[0], addr[1], addr[2], addr[3]);
-	printk("stubs used %ld, stubs max %ld\n"
-	       "init_stubs used %ld, init stubs max %ld\n"
-	       "got entries used %ld, gots max %ld\n"
+	printk("got entries used %ld, gots max %ld\n"
 	       "fdescs used %ld, fdescs max %ld\n",
-	       me->arch.stub_count, me->arch.stub_max,
-	       me->arch.init_stub_count, me->arch.init_stub_max,
 	       me->arch.got_count, me->arch.got_max,
 	       me->arch.fdesc_count, me->arch.fdesc_max);
 #endif
···
 				me->name, me->arch.got_count, MAX_GOTS);
 		return -EINVAL;
 	}
-	
+
+	kfree(me->arch.section);
+	me->arch.section = NULL;
+
 	/* no symbol table */
 	if(symhdr == NULL)
 		return 0;