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Subject[PATCH v2 28/59] objtool: Allow !PC relative relocations
From: Peter Zijlstra <peterz@infradead.org>

Objtool doesn't currently much like per-cpu usage in alternatives:

arch/x86/entry/entry_64.o: warning: objtool: .altinstr_replacement+0xf: unsupported relocation in alternatives section
f: 65 c7 04 25 00 00 00 00 00 00 00 80 movl $0x80000000,%gs:0x0 13: R_X86_64_32S __x86_call_depth

Since the R_X86_64_32S relocation is location invariant (it's
computation doesn't include P - the address of the location itself),
it can be trivially allowed.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
tools/objtool/arch/x86/decode.c | 42 +++++++++++++++++++++++++++++-----
tools/objtool/check.c | 6 +---
tools/objtool/include/objtool/arch.h | 6 ++--
tools/objtool/include/objtool/check.h | 17 +++++++------
4 files changed, 51 insertions(+), 20 deletions(-)

--- a/tools/objtool/arch/x86/decode.c
+++ b/tools/objtool/arch/x86/decode.c
@@ -73,6 +73,30 @@ unsigned long arch_jump_destination(stru
return insn->offset + insn->len + insn->immediate;
}

+bool arch_pc_relative_reloc(struct reloc *reloc)
+{
+ /*
+ * All relocation types where P (the address of the target)
+ * is included in the computation.
+ */
+ switch (reloc->type) {
+ case R_X86_64_PC8:
+ case R_X86_64_PC16:
+ case R_X86_64_PC32:
+ case R_X86_64_PC64:
+
+ case R_X86_64_PLT32:
+ case R_X86_64_GOTPC32:
+ case R_X86_64_GOTPCREL:
+ return true;
+
+ default:
+ break;
+ }
+
+ return false;
+}
+
#define ADD_OP(op) \
if (!(op = calloc(1, sizeof(*op)))) \
return -1; \
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1622,7 +1620,7 @@ static int handle_group_alt(struct objto
* accordingly.
*/
alt_reloc = insn_reloc(file, insn);
- if (alt_reloc &&
+ if (alt_reloc && arch_pc_relative_reloc(alt_reloc) &&
!arch_support_alt_relocation(special_alt, insn, alt_reloc)) {

WARN_FUNC("unsupported relocation in alternatives section",
--- a/tools/objtool/include/objtool/arch.h
+++ b/tools/objtool/include/objtool/arch.h
@@ -93,4 +91,6 @@ bool arch_is_rethunk(struct symbol *sym)

int arch_rewrite_retpolines(struct objtool_file *file);

+bool arch_pc_relative_reloc(struct reloc *reloc);
+
#endif /* _ARCH_H */

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