Re: [PATCH] arm64: ftrace: fix building without CONFIG_MODULES

[Will Deacon]

On Fri, Jun 09, 2017 at 08:57:31PM +0200, Arnd Bergmann wrote:
> On Fri, Jun 9, 2017 at 1:38 PM, Will Deacon <will.dea...@arm.com> wrote:
> > On Fri, Jun 09, 2017 at 12:27:06PM +0200, Arnd Bergmann wrote:
> >> When CONFIG_MODULES is disabled, we cannot dereference a module pointer:
> >>
> >> arch/arm64/kernel/ftrace.c: In function 'ftrace_make_call':
> >> arch/arm64/kernel/ftrace.c:107:36: error: dereferencing pointer to 
> >> incomplete type 'struct module'
> >>    trampoline = (unsigned long *)mod->arch.ftrace_trampoline;
> >>
> >> Also, the within_module() function is not defined:
> >>
> >> arch/arm64/kernel/ftrace.c: In function 'ftrace_make_nop':
> >> arch/arm64/kernel/ftrace.c:171:8: error: implicit declaration of function 
> >> 'within_module'; did you mean 'init_module'? 
> >> [-Werror=implicit-function-declaration]
> >>
> >> This addresses both by adding the appropriate stubs.
> >>
> >> Fixes: e71a4e1bebaf ("arm64: ftrace: add support for far branches to 
> >> dynamic ftrace")
> >> Signed-off-by: Arnd Bergmann <a...@arndb.de>
> >> ---
> >>  arch/arm64/include/asm/module.h | 6 ++++++
> >>  arch/arm64/kernel/ftrace.c      | 2 +-
> >>  include/linux/module.h          | 5 +++++
> >>  3 files changed, 12 insertions(+), 1 deletion(-)
> >
> > I can't seem to reproduce this simply by disabling MODULES in defconfig.
> > Could you share your .config, please?
> 
> This is the randconfig I used: https://pastebin.com/SfKBY7f8

Thanks, I was forgetting to enable ftrace. I think a simpler patch (and one
that I can just apply via arm64) is switching the IS_ENABLEDs out for
#ifdefs. See below.

Will

--->8

diff --git a/arch/arm64/kernel/ftrace.c b/arch/arm64/kernel/ftrace.c
index 8a42be0693c9..401aa27808a4 100644
--- a/arch/arm64/kernel/ftrace.c
+++ b/arch/arm64/kernel/ftrace.c
@@ -71,11 +71,12 @@ int ftrace_update_ftrace_func(ftrace_func_t func)
 int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 {
        unsigned long pc = rec->ip;
-       long offset = (long)pc - (long)addr;
        u32 old, new;
 
-       if (IS_ENABLED(CONFIG_ARM64_MODULE_PLTS) &&
-           (offset < -SZ_128M || offset >= SZ_128M)) {
+#ifdef CONFIG_ARM64_MODULE_PLTS
+       long offset = (long)pc - (long)addr;
+
+       if (offset < -SZ_128M || offset >= SZ_128M) {
                unsigned long *trampoline;
                struct module *mod;
 
@@ -121,6 +122,7 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned long 
addr)
                }
                addr = (unsigned long)&trampoline[1];
        }
+#endif /* CONFIG_ARM64_MODULE_PLTS */
 
        old = aarch64_insn_gen_nop();
        new = aarch64_insn_gen_branch_imm(pc, addr, AARCH64_INSN_BRANCH_LINK);
@@ -135,12 +137,13 @@ int ftrace_make_nop(struct module *mod, struct dyn_ftrace 
*rec,
                    unsigned long addr)
 {
        unsigned long pc = rec->ip;
-       long offset = (long)pc - (long)addr;
        bool validate = true;
        u32 old = 0, new;
 
-       if (IS_ENABLED(CONFIG_ARM64_MODULE_PLTS) &&
-           (offset < -SZ_128M || offset >= SZ_128M)) {
+#ifdef CONFIG_ARM64_MODULE_PLTS
+       long offset = (long)pc - (long)addr;
+
+       if (offset < -SZ_128M || offset >= SZ_128M) {
                u32 replaced;
 
                /*
@@ -177,6 +180,7 @@ int ftrace_make_nop(struct module *mod, struct dyn_ftrace 
*rec,
                old = aarch64_insn_gen_branch_imm(pc, addr,
                                                  AARCH64_INSN_BRANCH_LINK);
        }
+#endif /* CONFIG_ARM64_MODULE_PLTS */
 
        new = aarch64_insn_gen_nop();