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Date: Thu, 22 Jun 2023 12:54:32 +0200
From: Christophe Leroy <christophe.leroy@...roup.eu>
To: Michael Ellerman <mpe@...erman.id.au>,
Nicholas Piggin <npiggin@...il.com>,
Josh Poimboeuf <jpoimboe@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
Sathvika Vasireddy <sv@...ux.ibm.com>,
Naveen N Rao <naveen@...nel.org>
Cc: Christophe Leroy <christophe.leroy@...roup.eu>,
linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH v2 10/14] objtool: Add support for relative switch tables
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
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
Add support to objtool for relative tables, with a flag in order to
tell table by table if that table uses relative or absolute addressing.
And use correct size for 'long' instead of hard coding a size of '8'.
Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
---
tools/objtool/arch/powerpc/special.c | 2 +-
tools/objtool/arch/x86/special.c | 3 ++-
tools/objtool/check.c | 21 ++++++++++++++-------
tools/objtool/include/objtool/elf.h | 1 +
tools/objtool/include/objtool/special.h | 2 +-
5 files changed, 19 insertions(+), 10 deletions(-)
diff --git a/tools/objtool/arch/powerpc/special.c b/tools/objtool/arch/powerpc/special.c
index d33868147196..979b555b16ea 100644
--- a/tools/objtool/arch/powerpc/special.c
+++ b/tools/objtool/arch/powerpc/special.c
@@ -13,7 +13,7 @@ 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, bool *is_rel)
{
exit(-1);
}
diff --git a/tools/objtool/arch/x86/special.c b/tools/objtool/arch/x86/special.c
index 7c97b7391279..e7e1775f313a 100644
--- a/tools/objtool/arch/x86/special.c
+++ b/tools/objtool/arch/x86/special.c
@@ -92,7 +92,7 @@ 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, bool *is_rel)
{
struct reloc *text_reloc, *rodata_reloc;
struct section *table_sec;
@@ -141,5 +141,6 @@ struct reloc *arch_find_switch_table(struct objtool_file *file,
if (text_reloc->type == R_X86_64_PC32)
file->ignore_unreachables = true;
+ *is_rel = false;
return rodata_reloc;
}
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 8977cdf93f54..b810be087d7c 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -2053,7 +2053,7 @@ static int add_jump_table(struct objtool_file *file, struct instruction *insn,
struct instruction *dest_insn;
struct alternative *alt;
struct symbol *pfunc = insn_func(insn)->pfunc;
- unsigned int prev_offset = 0;
+ unsigned int offset, prev_offset = 0;
/*
* Each @reloc is a switch table relocation which points to the target
@@ -2066,7 +2066,7 @@ 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 != prev_offset + 8)
+ if (prev_offset && reloc->offset != prev_offset + elf_class_addrsize(file->elf))
break;
/* Detect function pointers from contiguous objects: */
@@ -2074,7 +2074,12 @@ static int add_jump_table(struct objtool_file *file, struct instruction *insn,
reloc->addend == pfunc->offset)
break;
- dest_insn = find_insn(file, reloc->sym->sec, reloc->addend);
+ if (table->jump_table_is_rel)
+ offset = reloc->addend + table->offset - reloc->offset;
+ else
+ offset = reloc->addend;
+
+ dest_insn = find_insn(file, reloc->sym->sec, offset);
if (!dest_insn)
break;
@@ -2107,8 +2112,8 @@ static int add_jump_table(struct objtool_file *file, struct instruction *insn,
* associated with it.
*/
static struct reloc *find_jump_table(struct objtool_file *file,
- struct symbol *func,
- struct instruction *insn)
+ struct symbol *func,
+ struct instruction *insn, bool *is_rel)
{
struct reloc *table_reloc;
struct instruction *dest_insn, *orig_insn = insn;
@@ -2132,7 +2137,7 @@ 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, is_rel);
if (!table_reloc)
continue;
dest_insn = find_insn(file, table_reloc->sym->sec, table_reloc->addend);
@@ -2154,6 +2159,7 @@ static void mark_func_jump_tables(struct objtool_file *file,
{
struct instruction *insn, *last = NULL;
struct reloc *reloc;
+ bool is_rel;
func_for_each_insn(file, func, insn) {
if (!last)
@@ -2176,9 +2182,10 @@ static void mark_func_jump_tables(struct objtool_file *file,
if (insn->type != INSN_JUMP_DYNAMIC)
continue;
- reloc = find_jump_table(file, func, insn);
+ reloc = find_jump_table(file, func, insn, &is_rel);
if (reloc) {
reloc->jump_table_start = true;
+ reloc->jump_table_is_rel = is_rel;
insn->_jump_table = reloc;
}
}
diff --git a/tools/objtool/include/objtool/elf.h b/tools/objtool/include/objtool/elf.h
index e1ca588eb69d..64aac87a4825 100644
--- a/tools/objtool/include/objtool/elf.h
+++ b/tools/objtool/include/objtool/elf.h
@@ -80,6 +80,7 @@ struct reloc {
s64 addend;
int idx;
bool jump_table_start;
+ bool jump_table_is_rel;
};
#define ELF_HASH_BITS 20
diff --git a/tools/objtool/include/objtool/special.h b/tools/objtool/include/objtool/special.h
index 86d4af9c5aa9..5edfc4c3e582 100644
--- a/tools/objtool/include/objtool/special.h
+++ b/tools/objtool/include/objtool/special.h
@@ -38,5 +38,5 @@ 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, bool *is_rel);
#endif /* _SPECIAL_H */
--
2.40.1
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