[PATCH v4 06/15] objtool: Add support for relative switch tables

[Christophe Leroy]

On powerpc, switch tables are relative, than means the address of the
table is added to the value of the entry in order to get the pointed
address: (r10 is the table address, r4 the index in the table)

      lis     r10,0		<== Load r10 with upper part of .rodata address
          R_PPC_ADDR16_HA     .rodata
      addi    r10,r10,0		<== Add lower part of .rodata address
          R_PPC_ADDR16_LO     .rodata
      lwzx    r8,r10,r4		<== Read table entry at r10 + r4 into r8
      add     r10,r8,r10	<== Add table address to read value
      mtctr   r10		<== Save calculated address in CTR
      bctr			<== Branch to address in CTR

      RELOCATION RECORDS FOR [.rodata]:
      OFFSET   TYPE              VALUE
      00000000 R_PPC_REL32       .text+0x0000054c
      00000004 R_PPC_REL32       .text+0x000003d0
	...

But for c_jump_tables it is not the case, they contain the
pointed address directly:

      lis     r28,0		<== Load r28 with upper .rodata..c_jump_table
          R_PPC_ADDR16_HA   .rodata..c_jump_table
      addi    r28,r28,0		<== Add lower part of .rodata..c_jump_table
          R_PPC_ADDR16_LO   .rodata..c_jump_table
      lwzx    r10,r28,r10	<== Read table entry at r10 + r28 into r10
      mtctr   r10		<== Save read value in CTR
      bctr			<== Branch to address in CTR

      RELOCATION RECORDS FOR [.rodata..c_jump_table]:
      OFFSET   TYPE              VALUE
      00000000 R_PPC_ADDR32      .text+0x00000dc8
      00000004 R_PPC_ADDR32      .text+0x00000dc8
	...

Add support to objtool for relative tables, based on the relocation
type which is R_PPC_REL32 for switch tables and R_PPC_ADDR32 for
C jump tables. Do the comparison using R_ABS32 and R_ABS64 which are
architecture agnostic.

And use correct size for 'long' instead of hard coding a size of '8'.

Signed-off-by: Christophe Leroy <christophe.leroy at csgroup.eu>
---
 tools/objtool/check.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index ae0019412123..5a6a87ddbf27 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1988,7 +1988,7 @@ static int add_jump_table(struct objtool_file *file, struct instruction *insn,
 	struct symbol *pfunc = insn_func(insn)->pfunc;
 	struct reloc *table = insn_jump_table(insn);
 	struct instruction *dest_insn;
-	unsigned int prev_offset = 0;
+	unsigned int offset, prev_offset = 0;
 	struct reloc *reloc = table;
 	struct alternative *alt;
 
@@ -2003,7 +2003,7 @@ static int add_jump_table(struct objtool_file *file, struct instruction *insn,
 			break;
 
 		/* Make sure the table entries are consecutive: */
-		if (prev_offset && reloc_offset(reloc) != prev_offset + 8)
+		if (prev_offset && reloc_offset(reloc) != prev_offset + elf_addr_size(file->elf))
 			break;
 
 		/* Detect function pointers from contiguous objects: */
@@ -2011,7 +2011,12 @@ static int add_jump_table(struct objtool_file *file, struct instruction *insn,
 		    reloc_addend(reloc) == pfunc->offset)
 			break;
 
-		dest_insn = find_insn(file, reloc->sym->sec, reloc_addend(reloc));
+		if (reloc_type(reloc) == R_ABS32 || reloc_type(reloc) == R_ABS64)
+			offset = reloc_addend(reloc);
+		else
+			offset = reloc_addend(reloc) + reloc_offset(table) - reloc_offset(reloc);
+
+		dest_insn = find_insn(file, reloc->sym->sec, offset);
 		if (!dest_insn)
 			break;
 
-- 
2.41.0