Re: [RFC] Crash on modpost, addend_386_rel()

[Atsushi Nemoto]

On Mon, 21 May 2007 22:01:27 -0400, Ben Collins <ben.collins@xxxxxxxxxx> wrote:
> Got this crash in modpost. Bisect blames this commit:
> 
> commit f892b7d480eec809a5dfbd6e65742b3f3155e50e
> Author: Atsushi Nemoto <anemo@xxxxxxxxxxxxx> 
> Date:   Thu May 17 01:14:38 2007 +0900
>     kbuild: make better section mismatch reports on i386, arm and mips

Sorry, the patch breaks CONFIG_RELOCATABLE=y build.  Actually I had
not tested with that configuration.

Linus already have reverted the commmit on git tree due to this breakage.

Unfortunately, fixing whole things in the _right_ way is somewhat out
of my ELF understanding.  Some help from ELF gurus are welcome!

Anyway, here is a updated patch tested on i386 (RELOCATABLE=y/n), arm,
and mips.  On calculation of 'location', sh_addr should be subtracted
(thank you for debugging, Linus).  And this patch contains an another
fix and an improvement of added_mips_rel
(kbuild-fix-and-improve-mips-rel-handling.patch in mm tree).


Subject: [PATCH] kbuild: make better section mismatch reports on i386, arm and mips (take 2)

On i386, ARM and MIPS, warn_sec_mismatch() sometimes fails to show
usefull symbol name.  This is because empty 'refsym' due to 0 r_addend
value.  This patch is to adjust r_addend value, consulting with
apply_relocate() routine in kernel code.

Signed-off-by: Atsushi Nemoto <anemo@xxxxxxxxxxxxx>
---
diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index 8e5610d..e0bd1cd 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -384,6 +384,8 @@ static int parse_elf(struct elf_info *info, const char *filename)
 		sechdrs[i].sh_size   = TO_NATIVE(sechdrs[i].sh_size);
 		sechdrs[i].sh_link   = TO_NATIVE(sechdrs[i].sh_link);
 		sechdrs[i].sh_name   = TO_NATIVE(sechdrs[i].sh_name);
+		sechdrs[i].sh_info   = TO_NATIVE(sechdrs[i].sh_info);
+		sechdrs[i].sh_addr   = TO_NATIVE(sechdrs[i].sh_addr);
 	}
 	/* Find symbol table. */
 	for (i = 1; i < hdr->e_shnum; i++) {
@@ -753,6 +755,8 @@ static Elf_Sym *find_elf_symbol(struct elf_info *elf, Elf_Addr addr,
 	for (sym = elf->symtab_start; sym < elf->symtab_stop; sym++) {
 		if (sym->st_shndx != relsym->st_shndx)
 			continue;
+		if (ELF_ST_TYPE(sym->st_info) == STT_SECTION)
+			continue;
 		if (sym->st_value == addr)
 			return sym;
 	}
@@ -895,6 +899,74 @@ static void warn_sec_mismatch(const char *modname, const char *fromsec,
 	}
 }
 
+static void addend_386_rel(struct elf_info *elf, int rsection, Elf_Rela *r)
+{
+	Elf_Shdr *sechdrs = elf->sechdrs;
+	unsigned int r_typ;
+	unsigned int *location;
+	int section = sechdrs[rsection].sh_info;
+
+	r_typ = ELF_R_TYPE(r->r_info);
+	location = (void *)elf->hdr + sechdrs[section].sh_offset +
+		(r->r_offset - sechdrs[section].sh_addr);
+	switch (r_typ) {
+	case R_386_32:
+		r->r_addend = TO_NATIVE(*location);
+		break;
+	case R_386_PC32:
+		r->r_addend = TO_NATIVE(*location) + 4;
+		break;
+	}
+}
+
+static void addend_arm_rel(struct elf_info *elf, int rsection, Elf_Rela *r)
+{
+	Elf_Shdr *sechdrs = elf->sechdrs;
+	unsigned int r_typ;
+	unsigned int *location;
+	int section = sechdrs[rsection].sh_info;
+
+	r_typ = ELF_R_TYPE(r->r_info);
+	location = (void *)elf->hdr + sechdrs[section].sh_offset +
+		(r->r_offset - sechdrs[section].sh_addr);
+	switch (r_typ) {
+	case R_ARM_ABS32:
+		r->r_addend = TO_NATIVE(*location);
+		break;
+	case R_ARM_PC24:
+		r->r_addend = ((TO_NATIVE(*location) & 0x00ffffff) << 2) + 8;
+		break;
+	}
+}
+
+static int addend_mips_rel(struct elf_info *elf, int rsection, Elf_Rela *r)
+{
+	Elf_Shdr *sechdrs = elf->sechdrs;
+	unsigned int r_typ;
+	unsigned int *location;
+	int section = sechdrs[rsection].sh_info;
+	unsigned int inst;
+
+	r_typ = ELF_R_TYPE(r->r_info);
+	if (r_typ == R_MIPS_HI16)
+		return 1;	/* skip this */
+	location = (void *)elf->hdr + sechdrs[section].sh_offset +
+		(r->r_offset - sechdrs[section].sh_addr);
+	inst = TO_NATIVE(*location);
+	switch (r_typ) {
+	case R_MIPS_LO16:
+		r->r_addend = inst & 0xffff;
+		break;
+	case R_MIPS_26:
+		r->r_addend = (inst & 0x03ffffff) << 2;
+		break;
+	case R_MIPS_32:
+		r->r_addend = inst;
+		break;
+	}
+	return 0;
+}
+
 /**
  * A module includes a number of sections that are discarded
  * either when loaded or when used as built-in.
@@ -938,8 +1010,11 @@ static void check_sec_ref(struct module *mod, const char *modname,
 				r.r_offset = TO_NATIVE(rela->r_offset);
 #if KERNEL_ELFCLASS == ELFCLASS64
 				if (hdr->e_machine == EM_MIPS) {
+					unsigned int r_typ;
 					r_sym = ELF64_MIPS_R_SYM(rela->r_info);
 					r_sym = TO_NATIVE(r_sym);
+					r_typ = ELF64_MIPS_R_TYPE(rela->r_info);
+					r.r_info = ELF64_R_INFO(r_sym, r_typ);
 				} else {
 					r.r_info = TO_NATIVE(rela->r_info);
 					r_sym = ELF_R_SYM(r.r_info);
@@ -972,8 +1047,11 @@ static void check_sec_ref(struct module *mod, const char *modname,
 				r.r_offset = TO_NATIVE(rel->r_offset);
 #if KERNEL_ELFCLASS == ELFCLASS64
 				if (hdr->e_machine == EM_MIPS) {
+					unsigned int r_typ;
 					r_sym = ELF64_MIPS_R_SYM(rel->r_info);
 					r_sym = TO_NATIVE(r_sym);
+					r_typ = ELF64_MIPS_R_TYPE(rel->r_info);
+					r.r_info = ELF64_R_INFO(r_sym, r_typ);
 				} else {
 					r.r_info = TO_NATIVE(rel->r_info);
 					r_sym = ELF_R_SYM(r.r_info);
@@ -983,6 +1061,14 @@ static void check_sec_ref(struct module *mod, const char *modname,
 				r_sym = ELF_R_SYM(r.r_info);
 #endif
 				r.r_addend = 0;
+				if (hdr->e_machine == EM_386)
+					addend_386_rel(elf, i, &r);
+				else if (hdr->e_machine == EM_ARM)
+					addend_arm_rel(elf, i, &r);
+				else if (hdr->e_machine == EM_MIPS) {
+					if (addend_mips_rel(elf, i, &r))
+						continue;
+				}
 				sym = elf->symtab_start + r_sym;
 				/* Skip special sections */
 				if (sym->st_shndx >= SHN_LORESERVE)
diff --git a/scripts/mod/modpost.h b/scripts/mod/modpost.h
index 0858caa..4156dd3 100644
--- a/scripts/mod/modpost.h
+++ b/scripts/mod/modpost.h
@@ -60,6 +60,9 @@ typedef union
 #define ELF64_MIPS_R_SYM(i) \
   ((__extension__ (_Elf64_Mips_R_Info_union)(i)).r_info_fields.r_sym)
 
+#define ELF64_MIPS_R_TYPE(i) \
+  ((__extension__ (_Elf64_Mips_R_Info_union)(i)).r_info_fields.r_type1)
+
 #if KERNEL_ELFDATA != HOST_ELFDATA
 
 static inline void __endian(const void *src, void *dest, unsigned int size)
-
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