[RFC PATCH v1 4/4] powerpc/static_call: Implement inline static calls

[Christophe Leroy]

Implement inline static calls:
- Put a 'bl' to the destination function
- Put a 'nop' when the destination function is NULL
- Put a 'li r3,0' when the destination is the RET0 function

For the time being it only works if the destination is
within 32Mb from the caller.

Signed-off-by: Christophe Leroy <christophe.leroy at csgroup.eu>
---
 arch/powerpc/Kconfig                          |  1 +
 arch/powerpc/include/asm/static_call.h        |  2 +
 arch/powerpc/kernel/static_call.c             | 41 ++++++++++++-------
 tools/objtool/arch/powerpc/include/arch/elf.h |  1 +
 4 files changed, 31 insertions(+), 14 deletions(-)

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 5ef8bf8eb202..3257a1c258d8 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -246,6 +246,7 @@ config PPC
 	select HAVE_STACKPROTECTOR		if PPC32 && $(cc-option,-mstack-protector-guard=tls -mstack-protector-guard-reg=r2)
 	select HAVE_STACKPROTECTOR		if PPC64 && $(cc-option,-mstack-protector-guard=tls -mstack-protector-guard-reg=r13)
 	select HAVE_STATIC_CALL			if PPC32
+	select HAVE_STATIC_CALL_INLINE		if PPC32
 	select HAVE_SYSCALL_TRACEPOINTS
 	select HAVE_VIRT_CPU_ACCOUNTING
 	select HUGETLB_PAGE_SIZE_VARIABLE	if PPC_BOOK3S_64 && HUGETLB_PAGE
diff --git a/arch/powerpc/include/asm/static_call.h b/arch/powerpc/include/asm/static_call.h
index de1018cc522b..e3d5d3823dac 100644
--- a/arch/powerpc/include/asm/static_call.h
+++ b/arch/powerpc/include/asm/static_call.h
@@ -26,4 +26,6 @@
 #define ARCH_DEFINE_STATIC_CALL_NULL_TRAMP(name)	__PPC_SCT(name, "blr")
 #define ARCH_DEFINE_STATIC_CALL_RET0_TRAMP(name)	__PPC_SCT(name, "b .+20")
 
+#define CALL_INSN_SIZE		4
+
 #endif /* _ASM_POWERPC_STATIC_CALL_H */
diff --git a/arch/powerpc/kernel/static_call.c b/arch/powerpc/kernel/static_call.c
index 863a7aa24650..fd25954cfd24 100644
--- a/arch/powerpc/kernel/static_call.c
+++ b/arch/powerpc/kernel/static_call.c
@@ -9,25 +9,38 @@ void arch_static_call_transform(void *site, void *tramp, void *func, bool tail)
 	int err;
 	bool is_ret0 = (func == __static_call_return0);
 	unsigned long target = (unsigned long)(is_ret0 ? tramp + PPC_SCT_RET0 : func);
-	bool is_short = is_offset_in_branch_range((long)target - (long)tramp);
-
-	if (!tramp)
-		return;
 
 	mutex_lock(&text_mutex);
 
-	if (func && !is_short) {
-		err = patch_instruction(tramp + PPC_SCT_DATA, ppc_inst(target));
-		if (err)
-			goto out;
+	if (tramp) {
+		bool is_short = is_offset_in_branch_range((long)target - (long)tramp);
+
+		if (func && !is_short) {
+			err = patch_instruction(tramp + PPC_SCT_DATA, ppc_inst(target));
+			if (err)
+				goto out;
+		}
+
+		if (!func)
+			err = patch_instruction(tramp, ppc_inst(PPC_RAW_BLR()));
+		else if (is_short)
+			err = patch_branch(tramp, target, 0);
+		else
+			err = patch_instruction(tramp, ppc_inst(PPC_RAW_NOP()));
 	}
 
-	if (!func)
-		err = patch_instruction(tramp, ppc_inst(PPC_RAW_BLR()));
-	else if (is_short)
-		err = patch_branch(tramp, target, 0);
-	else
-		err = patch_instruction(tramp, ppc_inst(PPC_RAW_NOP()));
+	if (site) {
+		bool is_short = is_offset_in_branch_range((long)func - (long)site);
+
+		if (!func)
+			err = patch_instruction(site, ppc_inst(PPC_RAW_NOP()));
+		else if (is_ret0)
+			err = patch_instruction(site, ppc_inst(PPC_RAW_LI(_R3, 0)));
+		else if (is_short)
+			err = patch_branch(site, target, BRANCH_SET_LINK);
+		else
+			panic("%s: function %pS is out of reach of %pS\n", __func__, func, site);
+	}
 out:
 	mutex_unlock(&text_mutex);
 
diff --git a/tools/objtool/arch/powerpc/include/arch/elf.h b/tools/objtool/arch/powerpc/include/arch/elf.h
index 3c8ebb7d2a6b..18784c764c14 100644
--- a/tools/objtool/arch/powerpc/include/arch/elf.h
+++ b/tools/objtool/arch/powerpc/include/arch/elf.h
@@ -4,5 +4,6 @@
 #define _OBJTOOL_ARCH_ELF
 
 #define R_NONE R_PPC_NONE
+#define R_REL32	R_PPC_REL32
 
 #endif /* _OBJTOOL_ARCH_ELF */
-- 
2.35.3