From 2982f0a024c85b1ce6eaf8147ffd43e28a361483 Mon Sep 17 00:00:00 2001
From: "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>
Date: Thu, 19 Apr 2018 12:34:07 +0530
Subject: [PATCH 8/9] powerpc64/module: Tighten detection of mcount call sites
with -mprofile-kernel
References: bsc#1088804
Patch-mainline: v4.18-rc1
Git-commit: 250122baed29d90c643be8809d75274336b98fb0
For R_PPC64_REL24 relocations, we suppress emitting instructions for TOC
load/restore in the relocation stub if the relocation is for _mcount()
call when using -mprofile-kernel ABI.
To detect this, we check if the preceding instructions are per the
standard set of instructions emitted by gcc: either the two instruction
sequence of 'mflr r0; std r0,16(r1)', or the more optimized variant of a
single 'mflr r0'. This is not sufficient since nothing prevents users
from hand coding sequences involving a 'mflr r0' followed by a 'bl'.
For removing the toc save instruction from the stub, we additionally
check if the symbol is "_mcount". Add the same check here as well.
Also rename is_early_mcount_callsite() to is_mprofile_mcount_callsite()
since that is what is being checked. The use of "early" is misleading
since there is nothing involving this function that qualifies as early.
Fixes: 153086644fd1f ("powerpc/ftrace: Add support for -mprofile-kernel ftrace ABI")
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Acked-by: Michal Suchanek <msuchanek@suse.de>
---
arch/powerpc/kernel/module_64.c | 15 +++++++++------
1 file changed, 9 insertions(+), 6 deletions(-)
diff --git a/arch/powerpc/kernel/module_64.c b/arch/powerpc/kernel/module_64.c
index e6d8a496438b..20dd82d565e2 100644
--- a/arch/powerpc/kernel/module_64.c
+++ b/arch/powerpc/kernel/module_64.c
@@ -442,8 +442,11 @@ static unsigned long stub_for_addr(const Elf64_Shdr *sechdrs,
}
#ifdef CC_USING_MPROFILE_KERNEL
-static bool is_early_mcount_callsite(u32 *instruction)
+static bool is_mprofile_mcount_callsite(const char *name, u32 *instruction)
{
+ if (strcmp("_mcount", name))
+ return false;
+
/*
* Check if this is one of the -mprofile-kernel sequences.
*/
@@ -475,8 +478,7 @@ static void squash_toc_save_inst(const char *name, unsigned long addr)
#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)
+static bool is_mprofile_mcount_callsite(const char *name, u32 *instruction)
{
return false;
}
@@ -484,11 +486,11 @@ static bool is_early_mcount_callsite(u32 *instruction)
/* We expect a noop next: if it is, replace it with instruction to
restore r2. */
-static int restore_r2(u32 *instruction, struct module *me)
+static int restore_r2(const char *name, u32 *instruction, struct module *me)
{
u32 *prev_insn = instruction - 1;
- if (is_early_mcount_callsite(prev_insn))
+ if (is_mprofile_mcount_callsite(name, prev_insn))
return 1;
/*
@@ -629,7 +631,8 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
value = stub_for_addr(sechdrs, value, me);
if (!value)
return -ENOENT;
- if (!restore_r2((u32 *)location + 1, me))
+ if (!restore_r2(strtab + sym->st_name,
+ (u32 *)location + 1, me))
return -ENOEXEC;
squash_toc_save_inst(strtab + sym->st_name, value);
--
2.13.6