Inserts a direct branch to the stub target when possible, replacing the
mtctr/btctr sequence.

The load into r12 could potentially be skipped too, but that change
would need to refactor the arguments to indicate that the address
does not have a separate local entry point.

This helps the static call implementation, where modules calling their
own trampolines are called through this stub and the trampoline is
easily within range of a direct branch.

Signed-off-by: Benjamin Gray <redacted>
---
  arch/powerpc/kernel/module_64.c | 13 +++++++++++++
  1 file changed, 13 insertions(+)

diff --git a/arch/powerpc/kernel/module_64.c b/arch/powerpc/kernel/module_64.c
index 4d816f7785b4..745ce9097dcf 100644
--- a/arch/powerpc/kernel/module_64.c
+++ b/arch/powerpc/kernel/module_64.c

@@ -141,6 +141,12 @@ static u32 ppc64_stub_insns[] = {
  	PPC_RAW_BCTR(),
  };
  
+#ifdef CONFIG_PPC64_ELF_ABI_V1
+#define PPC64_STUB_MTCTR_OFFSET 5
+#else
+#define PPC64_STUB_MTCTR_OFFSET 4
+#endif
+
  /* Count how many different 24-bit relocations (different symbol,
     different addend) */
  static unsigned int count_relocs(const Elf64_Rela *rela, unsigned int num)

@@ -429,6 +435,8 @@ static inline int create_stub(const Elf64_Shdr *sechdrs,
  	long reladdr;
  	func_desc_t desc;
  	int i;
+	u32 *jump_seq_addr = &entry->jump[PPC64_STUB_MTCTR_OFFSET];
+	ppc_inst_t direct;
  
  	if (is_mprofile_ftrace_call(name))
  		return create_ftrace_stub(entry, addr, me);

@@ -439,6 +447,11 @@ static inline int create_stub(const Elf64_Shdr *sechdrs,
  			return 0;
  	}
  
+	/* Replace indirect branch sequence with direct branch where possible */
+	if (!create_branch(&direct, jump_seq_addr, addr, 0))
+		if (patch_instruction(jump_seq_addr, direct))