Re: [RFC PATCH v1 2/4] objtool: Add R_REL32 macro

[Segher Boessenkool]

Hi!

On Wed, May 25, 2022 at 05:58:15PM +0200, Christophe Leroy wrote:
> In order to allow other architectures than x86 to use 32 bits
> relative relocations, define a R_REL32 macro that each architecture
> will define, in the same way as already done for R_NONE.

What are the expected semantics of this relocation?  It is PC-relative,
sure, but what is the destination?  S+A-P always?  That works for both
x86-64 and for PowerPC, but it should be written doen somewhere :-)


Segher

[RFC PATCH v1 2/4] objtool: Add R_REL32 macro

[Christophe Leroy]

In order to allow other architectures than x86 to use 32 bits
relative relocations, define a R_REL32 macro that each architecture
will define, in the same way as already done for R_NONE.

Signed-off-by: Christophe Leroy 
---
 tools/objtool/arch/x86/include/arch/elf.h |  1 +
 tools/objtool/check.c | 10 +-
 tools/objtool/orc_gen.c   |  2 +-
 3 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/tools/objtool/arch/x86/include/arch/elf.h 
b/tools/objtool/arch/x86/include/arch/elf.h
index 69cc4264b28a..8aa8c29607da 100644
--- a/tools/objtool/arch/x86/include/arch/elf.h
+++ b/tools/objtool/arch/x86/include/arch/elf.h
@@ -2,5 +2,6 @@
 #define _OBJTOOL_ARCH_ELF
 
 #define R_NONE R_X86_64_NONE
+#define R_REL32R_X86_64_PC32
 
 #endif /* _OBJTOOL_ARCH_ELF */
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 70be5a72e838..1627d14a01c9 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -650,7 +650,7 @@ static int create_static_call_sections(struct objtool_file 
*file)
/* populate reloc for 'addr' */
if (elf_add_reloc_to_insn(file->elf, sec,
  idx * sizeof(struct static_call_site),
- R_X86_64_PC32,
+ R_REL32,
  insn->sec, insn->offset))
return -1;
 
@@ -691,7 +691,7 @@ static int create_static_call_sections(struct objtool_file 
*file)
/* populate reloc for 'key' */
if (elf_add_reloc(file->elf, sec,
  idx * sizeof(struct static_call_site) + 4,
- R_X86_64_PC32, key_sym,
+ R_REL32, key_sym,
  is_sibling_call(insn) * 
STATIC_CALL_SITE_TAIL))
return -1;
 
@@ -735,7 +735,7 @@ static int create_retpoline_sites_sections(struct 
objtool_file *file)
 
if (elf_add_reloc_to_insn(file->elf, sec,
  idx * sizeof(int),
- R_X86_64_PC32,
+ R_REL32,
  insn->sec, insn->offset)) {
WARN("elf_add_reloc_to_insn: .retpoline_sites");
return -1;
@@ -787,7 +787,7 @@ static int create_ibt_endbr_seal_sections(struct 
objtool_file *file)
 
if (elf_add_reloc_to_insn(file->elf, sec,
  idx * sizeof(int),
- R_X86_64_PC32,
+ R_REL32,
  insn->sec, insn->offset)) {
WARN("elf_add_reloc_to_insn: .ibt_endbr_seal");
return -1;
@@ -3716,7 +3716,7 @@ static int validate_ibt_insn(struct objtool_file *file, 
struct instruction *insn
continue;
 
off = reloc->sym->offset;
-   if (reloc->type == R_X86_64_PC32 || reloc->type == 
R_X86_64_PLT32)
+   if (reloc->type == R_REL32 || reloc->type == R_X86_64_PLT32)
off += arch_dest_reloc_offset(reloc->addend);
else
off += reloc->addend;
diff --git a/tools/objtool/orc_gen.c b/tools/objtool/orc_gen.c
index 1f22b7ebae58..49a877b9c879 100644
--- a/tools/objtool/orc_gen.c
+++ b/tools/objtool/orc_gen.c
@@ -101,7 +101,7 @@ static int write_orc_entry(struct elf *elf, struct section 
*orc_sec,
orc->bp_offset = bswap_if_needed(elf, orc->bp_offset);
 
/* populate reloc for ip */
-   if (elf_add_reloc_to_insn(elf, ip_sec, idx * sizeof(int), R_X86_64_PC32,
+   if (elf_add_reloc_to_insn(elf, ip_sec, idx * sizeof(int), R_REL32,
  insn_sec, insn_off))
return -1;
 
-- 
2.35.3