powerpc/module: Only try to generate the ftrace_caller() stub once

Currently we generate the module stub for ftrace_caller() at the bottom
of apply_relocate_add(). However apply_relocate_add() is potentially
called more than once per module, which means we will try to generate
the ftrace_caller() stub multiple times.

Although the current code deals with that correctly, ie. it only
generates a stub the first time, it would be clearer to only try to
generate the stub once.

Note also on first reading it may appear that we generate a different
stub for each section that requires relocation, but that is not the
case. The code in stub_for_addr() that searches for an existing stub
uses sechdrs[me->arch.stubs_section], ie. the single stub section for
this module.

A cleaner approach is to only generate the ftrace_caller() stub once,
from module_finalize(). Although the original code didn't check to see
if the stub was actually generated correctly, it seems prudent to add a
check, so do that. And an additional benefit is we can clean the ifdefs
up a little.

Finally we must propagate the const'ness of some of the pointers passed
to module_finalize(), but that is also an improvement.

Reviewed-by: Balbir Singh <bsingharora@gmail.com>
Reviewed-by: Torsten Duwe <duwe@suse.de>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

1 files changed, 14 insertions, 6 deletions

diff --git a/arch/powerpc/kernel/module_32.c b/arch/powerpc/kernel/module_32.c
index 2c01665eb410..5a7a78f12562 100644
--- a/arch/powerpc/kernel/module_32.c
+++ b/arch/powerpc/kernel/module_32.c
@@ -181,7 +181,7 @@ static inline int entry_matches(struct ppc_plt_entry *entry, Elf32_Addr val)
 /* Set up a trampoline in the PLT to bounce us to the distant function */
 static uint32_t do_plt_call(void *location,
 			    Elf32_Addr val,
-			    Elf32_Shdr *sechdrs,
+			    const Elf32_Shdr *sechdrs,
 			    struct module *mod)
 {
 	struct ppc_plt_entry *entry;
@@ -294,11 +294,19 @@ int apply_relocate_add(Elf32_Shdr *sechdrs,
 			return -ENOEXEC;
 		}
 	}
+
+	return 0;
+}
+
 #ifdef CONFIG_DYNAMIC_FTRACE
-	module->arch.tramp =
-		do_plt_call(module->core_layout.base,
-			    (unsigned long)ftrace_caller,
-			    sechdrs, module);
-#endif
+int module_finalize_ftrace(struct module *module, const Elf_Shdr *sechdrs)
+{
+	module->arch.tramp = do_plt_call(module->core_layout.base,
+					 (unsigned long)ftrace_caller,
+					 sechdrs, module);
+	if (!module->arch.tramp)
+		return -ENOENT;
+
 	return 0;
 }
+#endif