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Commit 336a7b5d authored by Michael Ellerman's avatar Michael Ellerman
Browse files

powerpc/module: Create a special stub for ftrace_caller() 



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.

Reviewed-by: default avatarBalbir Singh <bsingharora@gmail.com>
Reviewed-by: default avatarTorsten Duwe <duwe@suse.de>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
parent f17c4e01

arch/powerpc/kernel/module_64.c

+68 −1
Original line number Diff line number Diff line
@@ -31,6 +31,7 @@ 
#include <asm/code-patching.h>

#include <linux/sort.h>

#include <asm/setup.h>

#include <asm/sections.h>



/* FIXME: We don't do .init separately.  To do this, we'd need to have

   a separate r2 value in the init and core section, and stub between
@@ -671,10 +672,76 @@ int apply_relocate_add(Elf64_Shdr *sechdrs, 
}



#ifdef CONFIG_DYNAMIC_FTRACE



#ifdef CC_USING_MPROFILE_KERNEL



#define PACATOC offsetof(struct paca_struct, kernel_toc)



/*

 * For mprofile-kernel we use a special stub for ftrace_caller() because we

 * can't rely on r2 containing this module's TOC when we enter the stub.

 *

 * That can happen if the function calling us didn't need to use the toc. In

 * that case it won't have setup r2, and the r2 value will be either the

 * kernel's toc, or possibly another modules toc.

 *

 * To deal with that this stub uses the kernel toc, which is always accessible

 * via the paca (in r13). The target (ftrace_caller()) is responsible for

 * saving and restoring the toc before returning.

 */

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 (from the paca) */

	reladdr = (unsigned long)ftrace_caller - kernel_toc_addr();

	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;

}

#else

static unsigned long create_ftrace_stub(const Elf64_Shdr *sechdrs, struct module *me)

{

	return 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);

	mod->arch.tramp = create_ftrace_stub(sechdrs, mod);



	if (!mod->arch.tramp)

		return -ENOENT;