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objtool: Make relocation in alternative handling arch dependent 

As pointed out by the comment in handle_group_alt(), support of
relocation for instructions in an alternative group depends on whether
arch specific kernel code handles it.

So, let objtool arch specific code decide whether a relocation for
the alternative section should be accepted.

Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Julien Thierry <jthierry@redhat.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
This commit is contained in:
Julien Thierry 2020-09-04 16:30:23 +01:00 committed by Josh Poimboeuf
parent eda3dc9058
commit 45245f51f9
4 changed files with 29 additions and 13 deletions
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13
tools/objtool/arch/x86/special.c
View File

@ -35,3 +35,16 @@ void arch_handle_alternative(unsigned short feature, struct special_alt *alt)
break;
}
}
bool arch_support_alt_relocation(struct special_alt *special_alt,
struct instruction *insn,
struct reloc *reloc)
{
/*
* The x86 alternatives code adjusts the offsets only when it
* encounters a branch instruction at the very beginning of the
* replacement group.
*/
return insn->offset == special_alt->new_off &&
(insn->type == INSN_CALL || is_static_jump(insn));
}

19
tools/objtool/check.c
View File

@ -110,12 +110,6 @@ static struct instruction *prev_insn_same_sym(struct objtool_file *file,
for (insn = next_insn_same_sec(file, insn); insn; \
insn = next_insn_same_sec(file, insn))
static bool is_static_jump(struct instruction *insn)
{
return insn->type == INSN_JUMP_CONDITIONAL ||
insn->type == INSN_JUMP_UNCONDITIONAL;
}
static bool is_sibling_call(struct instruction *insn)
{
/* An indirect jump is either a sibling call or a jump to a table. */
@ -972,6 +966,8 @@ static int handle_group_alt(struct objtool_file *file,
alt_group = alt_group_next_index++;
insn = *new_insn;
sec_for_each_insn_from(file, insn) {
struct reloc *alt_reloc;
if (insn->offset >= special_alt->new_off + special_alt->new_len)
break;
@ -988,14 +984,11 @@ static int handle_group_alt(struct objtool_file *file,
* .altinstr_replacement section, unless the arch's
* alternatives code can adjust the relative offsets
* accordingly.
*
* The x86 alternatives code adjusts the offsets only when it
* encounters a branch instruction at the very beginning of the
* replacement group.
*/
if ((insn->offset != special_alt->new_off ||
(insn->type != INSN_CALL && !is_static_jump(insn))) &&
find_reloc_by_dest_range(file->elf, insn->sec, insn->offset, insn->len)) {
alt_reloc = find_reloc_by_dest_range(file->elf, insn->sec,
insn->offset, insn->len);
if (alt_reloc &&
!arch_support_alt_relocation(special_alt, insn, alt_reloc)) {
WARN_FUNC("unsupported relocation in alternatives section",
insn->sec, insn->offset);

6
tools/objtool/check.h
View File

@ -48,6 +48,12 @@ struct instruction {
#endif
};
static inline bool is_static_jump(struct instruction *insn)
{
return insn->type == INSN_JUMP_CONDITIONAL ||
insn->type == INSN_JUMP_UNCONDITIONAL;
}
struct instruction *find_insn(struct objtool_file *file,
struct section *sec, unsigned long offset);

4
tools/objtool/special.h
View File

@ -7,6 +7,7 @@
#define _SPECIAL_H
#include <stdbool.h>
#include "check.h"
#include "elf.h"
struct special_alt {
@ -30,4 +31,7 @@ int special_get_alts(struct elf *elf, struct list_head *alts);
void arch_handle_alternative(unsigned short feature, struct special_alt *alt);
bool arch_support_alt_relocation(struct special_alt *special_alt,
struct instruction *insn,
struct reloc *reloc);
#endif /* _SPECIAL_H */