From 153086644fd1fb07fb3af84d9f11542a19b1e8b6 Mon Sep 17 00:00:00 2001 From: Torsten Duwe Date: Thu, 3 Mar 2016 15:26:59 +1100 Subject: powerpc/ftrace: Add support for -mprofile-kernel ftrace ABI The gcc switch -mprofile-kernel defines a new ABI for calling _mcount() very early in the function with minimal overhead. Although mprofile-kernel has been available since GCC 3.4, there were bugs which were only fixed recently. Currently it is known to work in GCC 4.9, 5 and 6. Additionally there are two possible code sequences generated by the flag, the first uses mflr/std/bl and the second is optimised to omit the std. Currently only gcc 6 has the optimised sequence. This patch supports both sequences. Initial work started by Vojtech Pavlik, used with permission. Key changes: - rework _mcount() to work for both the old and new ABIs. - implement new versions of ftrace_caller() and ftrace_graph_caller() which deal with the new ABI. - updates to __ftrace_make_nop() to recognise the new mcount calling sequence. - updates to __ftrace_make_call() to recognise the nop'ed sequence. - implement ftrace_modify_call(). - updates to the module loader to surpress the toc save in the module stub when calling mcount with the new ABI. Reviewed-by: Balbir Singh Signed-off-by: Torsten Duwe Signed-off-by: Michael Ellerman --- arch/powerpc/kernel/module_64.c | 49 ++++++++++++++++++++++++++++++++++++++--- 1 file changed, 46 insertions(+), 3 deletions(-) (limited to 'arch/powerpc/kernel/module_64.c') diff --git a/arch/powerpc/kernel/module_64.c b/arch/powerpc/kernel/module_64.c index 76c0963572f5..848b47499a27 100644 --- a/arch/powerpc/kernel/module_64.c +++ b/arch/powerpc/kernel/module_64.c @@ -42,7 +42,6 @@ --RR. */ #if defined(_CALL_ELF) && _CALL_ELF == 2 -#define R2_STACK_OFFSET 24 /* An address is simply the address of the function. */ typedef unsigned long func_desc_t; @@ -74,7 +73,6 @@ static unsigned int local_entry_offset(const Elf64_Sym *sym) return PPC64_LOCAL_ENTRY_OFFSET(sym->st_other); } #else -#define R2_STACK_OFFSET 40 /* An address is address of the OPD entry, which contains address of fn. */ typedef struct ppc64_opd_entry func_desc_t; @@ -451,17 +449,60 @@ static unsigned long stub_for_addr(const Elf64_Shdr *sechdrs, return (unsigned long)&stubs[i]; } +#ifdef CC_USING_MPROFILE_KERNEL +static bool is_early_mcount_callsite(u32 *instruction) +{ + /* + * Check if this is one of the -mprofile-kernel sequences. + */ + if (instruction[-1] == PPC_INST_STD_LR && + instruction[-2] == PPC_INST_MFLR) + return true; + + if (instruction[-1] == PPC_INST_MFLR) + return true; + + return false; +} + +/* + * In case of _mcount calls, do not save the current callee's TOC (in r2) into + * the original caller's stack frame. If we did we would clobber the saved TOC + * value of the original caller. + */ +static void squash_toc_save_inst(const char *name, unsigned long addr) +{ + struct ppc64_stub_entry *stub = (struct ppc64_stub_entry *)addr; + + /* Only for calls to _mcount */ + if (strcmp("_mcount", name) != 0) + return; + + stub->jump[2] = PPC_INST_NOP; +} +#else +static void squash_toc_save_inst(const char *name, unsigned long addr) { } + +/* without -mprofile-kernel, mcount calls are never early */ +static bool is_early_mcount_callsite(u32 *instruction) +{ + return false; +} +#endif + /* We expect a noop next: if it is, replace it with instruction to restore r2. */ static int restore_r2(u32 *instruction, struct module *me) { if (*instruction != PPC_INST_NOP) { + if (is_early_mcount_callsite(instruction - 1)) + return 1; pr_err("%s: Expect noop after relocate, got %08x\n", me->name, *instruction); return 0; } /* ld r2,R2_STACK_OFFSET(r1) */ - *instruction = 0xe8410000 | R2_STACK_OFFSET; + *instruction = PPC_INST_LD_TOC; return 1; } @@ -586,6 +627,8 @@ int apply_relocate_add(Elf64_Shdr *sechdrs, return -ENOENT; if (!restore_r2((u32 *)location + 1, me)) return -ENOEXEC; + + squash_toc_save_inst(strtab + sym->st_name, value); } else value += local_entry_offset(sym); -- cgit v1.2.3