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@csgroup.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 */
--
2.40.1On Thu, Jun 22, 2023 at 12:54:32PM +0200, Christophe Leroy wrote:
> 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'.
Again, see tip/objtool/core...
This one is going to be a little hard. It would be very good if you can
avoid growing struct reloc; Josh went through a ton of effort to shrink
it.
Would it work to use reloc->sym->is_rel_jumptable ? That still has a few
spare bits in it's bitfield.
> 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;
> };
Le 22/06/2023 à 13:48, Peter Zijlstra a écrit : > On Thu, Jun 22, 2023 at 12:54:32PM +0200, Christophe Leroy wrote: >> 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'. > > Again, see tip/objtool/core... > > This one is going to be a little hard. It would be very good if you can > avoid growing struct reloc; Josh went through a ton of effort to shrink > it. > > Would it work to use reloc->sym->is_rel_jumptable ? That still has a few > spare bits in it's bitfield. > I noticed that the relocation types are different, so the flag is indeed not needed. I have now done the following, will it work for x86 ? diff --git a/tools/objtool/check.c b/tools/objtool/check.c index ae4a1608d97e..05d789e6d3b6 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; Christophe
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