In order to support the new -mprofile-kernel ABI, we need to be able to
call from the module back to ftrace_caller() (in the kernel) without
using the module's r2. That is because the function in this module which
is calling ftrace_caller() may not have setup r2, if it doesn't
otherwise need it (ie. it accesses no globals).
To make that work we add a new stub which is used for calling
ftrace_caller(), which uses the kernel toc instead of the module toc.
Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
---
arch/powerpc/kernel/module_64.c | 48 ++++++++++++++++++++++++++++++++++++++++-
1 file changed, 47 insertions(+), 1 deletion(-)
diff --git a/arch/powerpc/kernel/module_64.c b/arch/powerpc/kernel/module_64.c
index 9629966e614b..e711d40a3b8f 100644
--- a/arch/powerpc/kernel/module_64.c
+++ b/arch/powerpc/kernel/module_64.c
@@ -671,10 +671,56 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
}
#ifdef CONFIG_DYNAMIC_FTRACE
+
+#define PACATOC offsetof(struct paca_struct, kernel_toc)
+
+static unsigned long create_ftrace_stub(const Elf64_Shdr *sechdrs, struct module *me)
+{
+ struct ppc64_stub_entry *entry;
+ unsigned int i, num_stubs;
+ static u32 stub_insns[] = {
+ 0xe98d0000 | PACATOC, /* ld r12,PACATOC(r13) */
+ 0x3d8c0000, /* addis r12,r12,<high> */
+ 0x398c0000, /* addi r12,r12,<low> */
+ 0x7d8903a6, /* mtctr r12 */
+ 0x4e800420, /* bctr */
+ };
+ long reladdr;
+
+ num_stubs = sechdrs[me->arch.stubs_section].sh_size / sizeof(*entry);
+
+ /* Find the next available stub entry */
+ entry = (void *)sechdrs[me->arch.stubs_section].sh_addr;
+ for (i = 0; i < num_stubs && stub_func_addr(entry->funcdata); i++, entry++);
+
+ if (i >= num_stubs) {
+ pr_err("%s: Unable to find a free slot for ftrace stub.\n", me->name);
+ return 0;
+ }
+
+ memcpy(entry->jump, stub_insns, sizeof(stub_insns));
+
+ /* Stub uses address relative to kernel_toc */
+ reladdr = (unsigned long)ftrace_caller - get_paca()->kernel_toc;
+ if (reladdr > 0x7FFFFFFF || reladdr < -(0x80000000L)) {
+ pr_err("%s: Address of ftrace_caller out of range of kernel_toc.\n", me->name);
+ return 0;
+ }
+
+ entry->jump[1] |= PPC_HA(reladdr);
+ entry->jump[2] |= PPC_LO(reladdr);
+
+ /* Eventhough we don't use funcdata in the stub, it's needed elsewhere. */
+ entry->funcdata = func_desc((unsigned long)ftrace_caller);
+ entry->magic = STUB_MAGIC;
+
+ return (unsigned long)entry;
+}
+
int module_finalize_ftrace(struct module *mod, const Elf_Shdr *sechdrs)
{
mod->arch.toc = my_r2(sechdrs, mod);
- mod->arch.tramp = stub_for_addr(sechdrs, (unsigned long)ftrace_caller, mod);
+ mod->arch.tramp = create_ftrace_stub(sechdrs, mod);
if (!mod->arch.tramp)
return -ENOENT;
--
2.5.0
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