From: Ard Biesheuvel <ardb@kernel.org>

In preparation for adding support for annotated jump tables, where
ELF relocations and symbols are used to describe the locations of jump
tables in the executable, refactor the jump table discovery logic so the
table size can be returned from arch_find_switch_table().

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 tools/objtool/arch/loongarch/special.c  |  3 +-
 tools/objtool/arch/powerpc/special.c    |  3 +-
 tools/objtool/arch/x86/special.c        |  4 ++-
 tools/objtool/check.c                   | 31 +++++++++++++-------
 tools/objtool/include/objtool/check.h   |  5 +++-
 tools/objtool/include/objtool/special.h |  3 +-
 6 files changed, 33 insertions(+), 16 deletions(-)

diff --git a/tools/objtool/arch/loongarch/special.c b/tools/objtool/arch/loongarch/special.c
index 9bba1e9318e0..87230ed570fd 100644
--- a/tools/objtool/arch/loongarch/special.c
+++ b/tools/objtool/arch/loongarch/special.c
@@ -9,7 +9,8 @@ bool arch_support_alt_relocation(struct special_alt *special_alt,
 }
 
 struct reloc *arch_find_switch_table(struct objtool_file *file,
-				     struct instruction *insn)
+				     struct instruction *insn,
+				     unsigned long *table_size)
 {
 	return NULL;
 }
diff --git a/tools/objtool/arch/powerpc/special.c b/tools/objtool/arch/powerpc/special.c
index d33868147196..51610689abf7 100644
--- a/tools/objtool/arch/powerpc/special.c
+++ b/tools/objtool/arch/powerpc/special.c
@@ -13,7 +13,8 @@ bool arch_support_alt_relocation(struct special_alt *special_alt,
 }
 
 struct reloc *arch_find_switch_table(struct objtool_file *file,
-				    struct instruction *insn)
+				     struct instruction *insn,
+				     unsigned long *table_size)
 {
 	exit(-1);
 }
diff --git a/tools/objtool/arch/x86/special.c b/tools/objtool/arch/x86/special.c
index 415e4d035e53..f8fb67636384 100644
--- a/tools/objtool/arch/x86/special.c
+++ b/tools/objtool/arch/x86/special.c
@@ -109,7 +109,8 @@ bool arch_support_alt_relocation(struct special_alt *special_alt,
  *    NOTE: MITIGATION_RETPOLINE made it harder still to decode dynamic jumps.
  */
 struct reloc *arch_find_switch_table(struct objtool_file *file,
-				    struct instruction *insn)
+				     struct instruction *insn,
+				     unsigned long *table_size)
 {
 	struct reloc  *text_reloc, *rodata_reloc;
 	struct section *table_sec;
@@ -150,5 +151,6 @@ struct reloc *arch_find_switch_table(struct objtool_file *file,
 	if (!rodata_reloc)
 		return NULL;
 
+	*table_size = 0;
 	return rodata_reloc;
 }
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 7f7981a93535..5f711ac5b43d 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -150,6 +150,15 @@ static inline struct reloc *insn_jump_table(struct instruction *insn)
 	return NULL;
 }
 
+static inline unsigned long insn_jump_table_size(struct instruction *insn)
+{
+	if (insn->type == INSN_JUMP_DYNAMIC ||
+	    insn->type == INSN_CALL_DYNAMIC)
+		return insn->_jump_table_size;
+
+	return 0;
+}
+
 static bool is_jump_table_jump(struct instruction *insn)
 {
 	struct alt_group *alt_group = insn->alt_group;
@@ -2099,6 +2108,7 @@ static int add_special_section_alts(struct objtool_file *file)
 static int add_jump_table(struct objtool_file *file, struct instruction *insn,
 			  struct reloc *next_table)
 {
+	unsigned long table_size = insn_jump_table_size(insn);
 	struct symbol *pfunc = insn_func(insn)->pfunc;
 	struct reloc *table = insn_jump_table(insn);
 	unsigned int rtype = reloc_type(table);
@@ -2116,6 +2126,8 @@ static int add_jump_table(struct objtool_file *file, struct instruction *insn,
 		unsigned long addend = reloc_addend(reloc);
 
 		/* Check for the end of the table: */
+		if (table_size && reloc_offset(reloc) - reloc_offset(table) >= table_size)
+			break;
 		if (reloc != table && reloc == next_table)
 			break;
 
@@ -2175,12 +2187,12 @@ static int add_jump_table(struct objtool_file *file, struct instruction *insn,
  * find_jump_table() - Given a dynamic jump, find the switch jump table
  * associated with it.
  */
-static struct reloc *find_jump_table(struct objtool_file *file,
-				      struct symbol *func,
-				      struct instruction *insn)
+static void find_jump_table(struct objtool_file *file, struct symbol *func,
+			    struct instruction *insn)
 {
 	struct reloc *table_reloc;
 	struct instruction *dest_insn, *orig_insn = insn;
+	unsigned long table_size;
 
 	/*
 	 * Backward search using the @first_jump_src links, these help avoid
@@ -2201,17 +2213,17 @@ static struct reloc *find_jump_table(struct objtool_file *file,
 		     insn->jump_dest->offset > orig_insn->offset))
 		    break;
 
-		table_reloc = arch_find_switch_table(file, insn);
+		table_reloc = arch_find_switch_table(file, insn, &table_size);
 		if (!table_reloc)
 			continue;
 		dest_insn = find_insn(file, table_reloc->sym->sec, reloc_addend(table_reloc));
 		if (!dest_insn || !insn_func(dest_insn) || insn_func(dest_insn)->pfunc != func)
 			continue;
 
-		return table_reloc;
+		orig_insn->_jump_table = table_reloc;
+		orig_insn->_jump_table_size = table_size;
+		break;
 	}
-
-	return NULL;
 }
 
 /*
@@ -2222,7 +2234,6 @@ static void mark_func_jump_tables(struct objtool_file *file,
 				    struct symbol *func)
 {
 	struct instruction *insn, *last = NULL;
-	struct reloc *reloc;
 
 	func_for_each_insn(file, func, insn) {
 		if (!last)
@@ -2245,9 +2256,7 @@ static void mark_func_jump_tables(struct objtool_file *file,
 		if (insn->type != INSN_JUMP_DYNAMIC)
 			continue;
 
-		reloc = find_jump_table(file, func, insn);
-		if (reloc)
-			insn->_jump_table = reloc;
+		find_jump_table(file, func, insn);
 	}
 }
 
diff --git a/tools/objtool/include/objtool/check.h b/tools/objtool/include/objtool/check.h
index daa46f1f0965..e1cd13cd28a3 100644
--- a/tools/objtool/include/objtool/check.h
+++ b/tools/objtool/include/objtool/check.h
@@ -71,7 +71,10 @@ struct instruction {
 	struct instruction *first_jump_src;
 	union {
 		struct symbol *_call_dest;
-		struct reloc *_jump_table;
+		struct {
+			struct reloc *_jump_table;
+			unsigned long _jump_table_size;
+		};
 	};
 	struct alternative *alts;
 	struct symbol *sym;
diff --git a/tools/objtool/include/objtool/special.h b/tools/objtool/include/objtool/special.h
index 89ee12b1a138..e049679bb17b 100644
--- a/tools/objtool/include/objtool/special.h
+++ b/tools/objtool/include/objtool/special.h
@@ -38,5 +38,6 @@ bool arch_support_alt_relocation(struct special_alt *special_alt,
 				 struct instruction *insn,
 				 struct reloc *reloc);
 struct reloc *arch_find_switch_table(struct objtool_file *file,
-				    struct instruction *insn);
+				     struct instruction *insn,
+				     unsigned long *table_size);
 #endif /* _SPECIAL_H */
-- 
2.47.0.rc0.187.ge670bccf7e-goog

On Thu, Oct 10, 2024 at 02:28:04PM +0200, Ard Biesheuvel wrote:
> @@ -2222,7 +2234,6 @@ static void mark_func_jump_tables(struct objtool_file *file,
>  				    struct symbol *func)
>  {
>  	struct instruction *insn, *last = NULL;
> -	struct reloc *reloc;
>  
>  	func_for_each_insn(file, func, insn) {
>  		if (!last)
> @@ -2245,9 +2256,7 @@ static void mark_func_jump_tables(struct objtool_file *file,
>  		if (insn->type != INSN_JUMP_DYNAMIC)
>  			continue;
>  
> -		reloc = find_jump_table(file, func, insn);
> -		if (reloc)
> -			insn->_jump_table = reloc;
> +		find_jump_table(file, func, insn);

Can we detect the annotation here, and if it exists, pivot to a separate
generic implementation which skips all the arch-specific code and hacks?

That way we could keep the "ugly" separate, and also have all arches
supported by default.

-- 
Josh

On Thu, 10 Oct 2024 at 21:52, Josh Poimboeuf <jpoimboe@kernel.org> wrote:
>
> On Thu, Oct 10, 2024 at 02:28:04PM +0200, Ard Biesheuvel wrote:
> > @@ -2222,7 +2234,6 @@ static void mark_func_jump_tables(struct objtool_file *file,
> >                                   struct symbol *func)
> >  {
> >       struct instruction *insn, *last = NULL;
> > -     struct reloc *reloc;
> >
> >       func_for_each_insn(file, func, insn) {
> >               if (!last)
> > @@ -2245,9 +2256,7 @@ static void mark_func_jump_tables(struct objtool_file *file,
> >               if (insn->type != INSN_JUMP_DYNAMIC)
> >                       continue;
> >
> > -             reloc = find_jump_table(file, func, insn);
> > -             if (reloc)
> > -                     insn->_jump_table = reloc;
> > +             find_jump_table(file, func, insn);
>
> Can we detect the annotation here, and if it exists, pivot to a separate
> generic implementation which skips all the arch-specific code and hacks?
>
> That way we could keep the "ugly" separate, and also have all arches
> supported by default.
>

I had a stab at this, and while the code changes are a bit intrusive,
the end result is much better for it (IMHO).

In the end, the logic in arch_find_switch_table() is mostly generic
anyway, but it is the code traversal in check.c that is the "ugly". So
I moved lots of things around. I'll send that out before signing off
today.