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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: Balbir Singh <bsingharora@gmail.com>
Reviewed-by: Torsten Duwe <duwe@suse.de>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
This commit is contained in:
Michael Ellerman 2016-03-03 15:26:56 +11:00
parent f17c4e01e9
commit 336a7b5dd8
1 changed files with 68 additions and 1 deletions
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69
arch/powerpc/kernel/module_64.c
View File

@ -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;