[PATCH v4 08/15] objtool: Track general purpose register used for switch table base

[Christophe Leroy]

A function can contain nested switch tables using different registers
as base address.

In order to avoid failure in tracking those switch tables, the register
containing the base address needs to be taken into account.

To do so, add a 5 bits field in struct instruction that will hold the
ID of the register containing the base address of the switch table and
take that register into account during the backward search in order to
not stop the walk when encountering a jump related to another switch
table.

On architectures not handling it, the ID stays nul and has no impact
on the search.

To enable that, also provide to arch_find_switch_table() the dynamic
instruction related to a table search.

Also allow prev_insn_same_sec() to be used outside check.c so that
architectures can backward walk through instruction to find out which
register is used as base address for a switch table.

Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
---
 tools/objtool/arch/powerpc/special.c    | 3 ++-
 tools/objtool/arch/x86/special.c        | 3 ++-
 tools/objtool/check.c                   | 9 +++++----
 tools/objtool/include/objtool/check.h   | 6 ++++--
 tools/objtool/include/objtool/special.h | 3 ++-
 5 files changed, 15 insertions(+), 9 deletions(-)

diff --git a/tools/objtool/arch/powerpc/special.c b/tools/objtool/arch/powerpc/special.c
index d33868147196..a7dd2559b536 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,
+				     struct instruction *orig_insn)
 {
 	exit(-1);
 }
diff --git a/tools/objtool/arch/x86/special.c b/tools/objtool/arch/x86/special.c
index 8e8302fe909f..8cf17d94c69b 100644
--- a/tools/objtool/arch/x86/special.c
+++ b/tools/objtool/arch/x86/special.c
@@ -86,7 +86,8 @@ bool arch_support_alt_relocation(struct special_alt *special_alt,
  *    NOTE: 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,
+				     struct instruction *orig_insn)
 {
 	struct reloc  *text_reloc, *rodata_reloc;
 	struct section *table_sec;
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index d51f47c4a3bd..be413c578588 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -80,8 +80,8 @@ static struct instruction *next_insn_same_func(struct objtool_file *file,
 	return find_insn(file, func->cfunc->sec, func->cfunc->offset);
 }
 
-static struct instruction *prev_insn_same_sec(struct objtool_file *file,
-					      struct instruction *insn)
+struct instruction *prev_insn_same_sec(struct objtool_file *file,
+				       struct instruction *insn)
 {
 	if (insn->idx == 0) {
 		if (insn->prev_len)
@@ -2064,7 +2064,8 @@ static struct reloc *find_jump_table(struct objtool_file *file,
 	     insn && insn_func(insn) && insn_func(insn)->pfunc == func;
 	     insn = insn->first_jump_src ?: prev_insn_same_sym(file, insn)) {
 
-		if (insn != orig_insn && insn->type == INSN_JUMP_DYNAMIC)
+		if (insn != orig_insn && insn->type == INSN_JUMP_DYNAMIC &&
+		    insn->gpr == orig_insn->gpr)
 			break;
 
 		/* allow small jumps within the range */
@@ -2074,7 +2075,7 @@ 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, orig_insn);
 		if (!table_reloc)
 			continue;
 
diff --git a/tools/objtool/include/objtool/check.h b/tools/objtool/include/objtool/check.h
index daa46f1f0965..660ea9d0393e 100644
--- a/tools/objtool/include/objtool/check.h
+++ b/tools/objtool/include/objtool/check.h
@@ -63,8 +63,9 @@ struct instruction {
 	    noendbr		: 1,
 	    unret		: 1,
 	    visited		: 4,
-	    no_reloc		: 1;
-		/* 10 bit hole */
+	    no_reloc		: 1,
+	    gpr			: 5;
+		/* 5 bit hole */
 
 	struct alt_group *alt_group;
 	struct instruction *jump_dest;
@@ -115,6 +116,7 @@ struct instruction *find_insn(struct objtool_file *file,
 			      struct section *sec, unsigned long offset);
 
 struct instruction *next_insn_same_sec(struct objtool_file *file, struct instruction *insn);
+struct instruction *prev_insn_same_sec(struct objtool_file *file, struct instruction *insn);
 
 #define sec_for_each_insn(file, _sec, insn)				\
 	for (insn = find_insn(file, _sec, 0);				\
diff --git a/tools/objtool/include/objtool/special.h b/tools/objtool/include/objtool/special.h
index 86d4af9c5aa9..4128a479d76e 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,
+				     struct instruction *orig_insn);
 #endif /* _SPECIAL_H */
-- 
2.41.0