Commit 9365e23b authored by Naveen N Rao's avatar Naveen N Rao Committed by Michael Ellerman
Browse files

powerpc/ftrace: Simplify ftrace_make_call() 



Now that we validate the ftrace location during initialization in
ftrace_init_nop(), we can simplify ftrace_make_call() to replace the nop
without worrying about the instructions surrounding the ftrace location.
Note that we continue to ensure that we have a nop at the ftrace
location before patching it.

Signed-off-by: default avatarNaveen N Rao <naveen@kernel.org>
Reviewed-by: default avatarChristophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/2d28866d2f556488a663981abe5621511efb207b.1687166935.git.naveen@kernel.org
parent 562bde0b

arch/powerpc/kernel/trace/ftrace.c

+31 −156
Original line number Diff line number Diff line
@@ -129,162 +129,6 @@ static unsigned long find_ftrace_tramp(unsigned long ip) 
	return 0;

}



#ifdef CONFIG_MODULES

/*

 * Examine the existing instructions for __ftrace_make_call.

 * They should effectively be a NOP, and follow formal constraints,

 * depending on the ABI. Return false if they don't.

 */

static bool expected_nop_sequence(void *ip, ppc_inst_t op0, ppc_inst_t op1)

{

	if (IS_ENABLED(CONFIG_DYNAMIC_FTRACE_WITH_REGS))

		return ppc_inst_equal(op0, ppc_inst(PPC_RAW_NOP()));

	else

		return ppc_inst_equal(op0, ppc_inst(PPC_RAW_BRANCH(8))) &&

		       ppc_inst_equal(op1, ppc_inst(PPC_INST_LD_TOC));

}



static int

__ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)

{

	ppc_inst_t op[2];

	void *ip = (void *)rec->ip;

	unsigned long entry, ptr, tramp;

	struct module *mod = rec->arch.mod;



	/* read where this goes */

	if (copy_inst_from_kernel_nofault(op, ip))

		return -EFAULT;



	if (!IS_ENABLED(CONFIG_DYNAMIC_FTRACE_WITH_REGS) &&

	    copy_inst_from_kernel_nofault(op + 1, ip + 4))

		return -EFAULT;



	if (!expected_nop_sequence(ip, op[0], op[1])) {

		pr_err("Unexpected call sequence at %p: %08lx %08lx\n", ip,

		       ppc_inst_as_ulong(op[0]), ppc_inst_as_ulong(op[1]));

		return -EINVAL;

	}



	/* If we never set up ftrace trampoline(s), then bail */

	if (!mod->arch.tramp ||

	    (IS_ENABLED(CONFIG_DYNAMIC_FTRACE_WITH_REGS) && !mod->arch.tramp_regs)) {

		pr_err("No ftrace trampoline\n");

		return -EINVAL;

	}



	if (IS_ENABLED(CONFIG_DYNAMIC_FTRACE_WITH_REGS) && rec->flags & FTRACE_FL_REGS)

		tramp = mod->arch.tramp_regs;

	else

		tramp = mod->arch.tramp;



	if (module_trampoline_target(mod, tramp, &ptr)) {

		pr_err("Failed to get trampoline target\n");

		return -EFAULT;

	}



	pr_devel("trampoline target %lx", ptr);



	entry = ppc_global_function_entry((void *)addr);

	/* This should match what was called */

	if (ptr != entry) {

		pr_err("addr %lx does not match expected %lx\n", ptr, entry);

		return -EINVAL;

	}



	if (patch_branch(ip, tramp, BRANCH_SET_LINK)) {

		pr_err("REL24 out of range!\n");

		return -EINVAL;

	}



	return 0;

}

#else

static int __ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)

{

	return 0;

}

#endif /* CONFIG_MODULES */



static int __ftrace_make_call_kernel(struct dyn_ftrace *rec, unsigned long addr)

{

	ppc_inst_t op;

	void *ip = (void *)rec->ip;

	unsigned long tramp, entry, ptr;



	/* Make sure we're being asked to patch branch to a known ftrace addr */

	entry = ppc_global_function_entry((void *)ftrace_caller);

	ptr = ppc_global_function_entry((void *)addr);



	if (ptr != entry && IS_ENABLED(CONFIG_DYNAMIC_FTRACE_WITH_REGS))

		entry = ppc_global_function_entry((void *)ftrace_regs_caller);



	if (ptr != entry) {

		pr_err("Unknown ftrace addr to patch: %ps\n", (void *)ptr);

		return -EINVAL;

	}



	/* Make sure we have a nop */

	if (copy_inst_from_kernel_nofault(&op, ip)) {

		pr_err("Unable to read ftrace location %p\n", ip);

		return -EFAULT;

	}



	if (!ppc_inst_equal(op, ppc_inst(PPC_RAW_NOP()))) {

		pr_err("Unexpected call sequence at %p: %08lx\n",

		       ip, ppc_inst_as_ulong(op));

		return -EINVAL;

	}



	tramp = find_ftrace_tramp((unsigned long)ip);

	if (!tramp) {

		pr_err("No ftrace trampolines reachable from %ps\n", ip);

		return -EINVAL;

	}



	if (patch_branch(ip, tramp, BRANCH_SET_LINK)) {

		pr_err("Error patching branch to ftrace tramp!\n");

		return -EINVAL;

	}



	return 0;

}



int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)

{

	unsigned long ip = rec->ip;

	ppc_inst_t old, new;



	/*

	 * If the calling address is more that 24 bits away,

	 * then we had to use a trampoline to make the call.

	 * Otherwise just update the call site.

	 */

	if (test_24bit_addr(ip, addr)) {

		/* within range */

		old = ppc_inst(PPC_RAW_NOP());

		new = ftrace_call_replace(ip, addr, 1);

		return ftrace_modify_code(ip, old, new);

	} else if (core_kernel_text(ip)) {

		return __ftrace_make_call_kernel(rec, addr);

	} else if (!IS_ENABLED(CONFIG_MODULES)) {

		/* We should not get here without modules */

		return -EINVAL;

	}



	/*

	 * Out of range jumps are called from modules.

	 * Being that we are converting from nop, it had better

	 * already have a module defined.

	 */

	if (!rec->arch.mod) {

		pr_err("No module loaded\n");

		return -EINVAL;

	}



	return __ftrace_make_call(rec, addr);

}



#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS

#ifdef CONFIG_MODULES

static int
@@ -419,6 +263,37 @@ int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr, 
}

#endif



int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)

{

	unsigned long tramp, ip = rec->ip;

	ppc_inst_t old, new;

	struct module *mod;



	old = ppc_inst(PPC_RAW_NOP());

	if (is_offset_in_branch_range(addr - ip)) {

		/* Within range */

		new = ftrace_create_branch_inst(ip, addr, 1);

		return ftrace_modify_code(ip, old, new);

	} else if (core_kernel_text(ip)) {

		/* We would be branching to one of our ftrace tramps */

		tramp = find_ftrace_tramp(ip);

		if (!tramp) {

			pr_err("0x%lx: No ftrace trampolines reachable\n", ip);

			return -EINVAL;

		}

		new = ftrace_create_branch_inst(ip, tramp, 1);

		return ftrace_modify_code(ip, old, new);

	} else if (IS_ENABLED(CONFIG_MODULES)) {

		/* Module code would be going to one of the module stubs */

		mod = rec->arch.mod;

		tramp = (addr == (unsigned long)ftrace_caller ? mod->arch.tramp : mod->arch.tramp_regs);

		new = ftrace_create_branch_inst(ip, tramp, 1);

		return ftrace_modify_code(ip, old, new);

	}



	return -EINVAL;

}



int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec, unsigned long addr)

{

	unsigned long tramp, ip = rec->ip;