[PATCH v3 2/8] powerpc/module: Only try to generate the ftrace_caller() stub once

Michael Ellerman
2016-03-03T04:27:09Z

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>
---
arch/powerpc/include/asm/module.h | 9 +++++++++
arch/powerpc/kernel/module.c | 5 +++++
arch/powerpc/kernel/module_32.c | 20 ++++++++++++++------
arch/powerpc/kernel/module_64.c | 22 ++++++++++++++--------
4 files changed, 42 insertions(+), 14 deletions(-)

v3: Fix compile error on 32-bit ! :}
v2: Add error checking on 32-bit for consistency.

diff --git a/arch/powerpc/include/asm/module.h b/arch/powerpc/include/asm/module.h
index dcfcad139bcc..74d25a749018 100644
--- a/arch/powerpc/include/asm/module.h
+++ b/arch/powerpc/include/asm/module.h
@@ -82,6 +82,15 @@ bool is_module_trampoline(u32 *insns);
int module_trampoline_target(struct module *mod, u32 *trampoline,
unsigned long *target);

+#ifdef CONFIG_DYNAMIC_FTRACE
+int module_finalize_ftrace(struct module *mod, const Elf_Shdr *sechdrs);
+#else
+static inline int module_finalize_ftrace(struct module *mod, const Elf_Shdr *sechdrs)
+{
+ return 0;
+}
+#endif
+
struct exception_table_entry;
void sort_ex_table(struct exception_table_entry *start,
struct exception_table_entry *finish);
diff --git a/arch/powerpc/kernel/module.c b/arch/powerpc/kernel/module.c
index 9547381b631a..d1f1b35bf0c7 100644
--- a/arch/powerpc/kernel/module.c
+++ b/arch/powerpc/kernel/module.c
@@ -47,6 +47,11 @@ int module_finalize(const Elf_Ehdr *hdr,
const Elf_Shdr *sechdrs, struct module *me)
{
const Elf_Shdr *sect;
+ int rc;
+
+ rc = module_finalize_ftrace(me, sechdrs);
+ if (rc)
+ return rc;

/* Apply feature fixups */
sect = find_section(hdr, sechdrs, "__ftr_fixup");
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
diff --git a/arch/powerpc/kernel/module_64.c b/arch/powerpc/kernel/module_64.c
index 08b7a40de5f8..00314b31a0d4 100644
--- a/arch/powerpc/kernel/module_64.c
+++ b/arch/powerpc/kernel/module_64.c
@@ -413,7 +413,7 @@ int module_frob_arch_sections(Elf64_Ehdr *hdr,
/* r2 is the TOC pointer: it actually points 0x8000 into the TOC (this
gives the value maximum span in an instruction which uses a signed
offset) */
-static inline unsigned long my_r2(Elf64_Shdr *sechdrs, struct module *me)
+static inline unsigned long my_r2(const Elf64_Shdr *sechdrs, struct module *me)
{
return sechdrs[me->arch.toc_section].sh_addr + 0x8000;
}
@@ -426,7 +426,7 @@ static inline unsigned long my_r2(Elf64_Shdr *sechdrs, struct module *me)
#define PPC_HA(v) PPC_HI ((v) + 0x8000)

/* Patch stub to reference function and correct r2 value. */
-static inline int create_stub(Elf64_Shdr *sechdrs,
+static inline int create_stub(const Elf64_Shdr *sechdrs,
struct ppc64_stub_entry *entry,
unsigned long addr,
struct module *me)
@@ -452,7 +452,7 @@ static inline int create_stub(Elf64_Shdr *sechdrs,

/* Create stub to jump to function described in this OPD/ptr: we need the
stub to set up the TOC ptr (r2) for the function. */
-static unsigned long stub_for_addr(Elf64_Shdr *sechdrs,
+static unsigned long stub_for_addr(const Elf64_Shdr *sechdrs,
unsigned long addr,
struct module *me)
{
@@ -693,12 +693,18 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
}
}

+ return 0;
+}
+
#ifdef CONFIG_DYNAMIC_FTRACE
- me->arch.toc = my_r2(sechdrs, me);
- me->arch.tramp = stub_for_addr(sechdrs,
- (unsigned long)ftrace_caller,
- me);
-#endif
+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);
+
+ if (!mod->arch.tramp)
+ return -ENOENT;

return 0;
}
+#endif
--
2.5.0