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Message-ID: <20210323222230.2d63hdcxq6strbug@e107158-lin>
Date: Tue, 23 Mar 2021 22:22:30 +0000
From: Qais Yousef <qais.yousef@....com>
To: Alexander Sverdlin <alexander.sverdlin@...ia.com>
Cc: Steven Rostedt <rostedt@...dmis.org>,
Ingo Molnar <mingo@...hat.com>,
Russell King <linux@...linux.org.uk>,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
Ard Biesheuvel <ardb@...nel.org>,
Linus Walleij <linus.walleij@...aro.org>,
Florian Fainelli <f.fainelli@...il.com>
Subject: Re: [PATCH v7 2/2] ARM: ftrace: Add MODULE_PLTS support
Hi Alexander
On 03/22/21 18:02, Alexander Sverdlin wrote:
> Hi Qais,
>
> On 22/03/2021 17:32, Qais Yousef wrote:
> > Yes you're right. I was a bit optimistic on CONFIG_DYNAMIC_FTRACE will imply
> > CONFIG_ARM_MODULE_PLTS is enabled too.
> >
> > It only has an impact on reducing ifdefery when calling
> >
> > ftrace_call_replace_mod(rec->arch.mod, ...)
> >
> > Should be easy to wrap rec->arch.mod with its own accessor that will return
> > NULL if !CONFIG_ARM_MODULE_PLTS or just ifdef the functions.
> >
> > Up to Alexander to pick what he prefers :-)
>
> well, I of course prefer v7 as-is, because this review is running longer than two
> years and I actually hope these patches to be finally merged at some point.
> But you are welcome to optimize them with follow up patches :)
I appreciate that and thanks a lot for your effort. My attempt to review and
test here is to help in getting this merged.
FWIW my main concern is about duplicating the range check in
ftrace_call_replace() and using magic values that already exist in
__arm_gen_branch_{arm, thumb2}() and better remain encapsulated there.
Thanks
--
Qais Yousef
----->8------
diff --git a/arch/arm/include/asm/ftrace.h b/arch/arm/include/asm/ftrace.h
index a4dbac07e4ef..8545b3ff8317 100644
--- a/arch/arm/include/asm/ftrace.h
+++ b/arch/arm/include/asm/ftrace.h
@@ -25,6 +25,27 @@ static inline unsigned long ftrace_call_adjust(unsigned long addr)
/* With Thumb-2, the recorded addresses have the lsb set */
return addr & ~1;
}
+
+#ifdef CONFIG_ARM_MODULE_PLTS
+static inline void ftrace_set_mod(struct dyn_arch_ftrace *arch, struct module *mod)
+{
+ arch->mod = mod;
+}
+
+static inline struct module *ftrace_get_mod(struct dyn_arch_ftrace *arch)
+{
+ return arch->mod;
+}
+#else
+static inline void ftrace_set_mod(struct dyn_arch_ftrace *arch, struct module *mod)
+{
+}
+
+static inline struct module *ftrace_get_mod(struct dyn_arch_ftrace *arch)
+{
+ return NULL;
+}
+#endif
#endif
#endif
diff --git a/arch/arm/include/asm/insn.h b/arch/arm/include/asm/insn.h
index f20e08ac85ae..71c3edefe629 100644
--- a/arch/arm/include/asm/insn.h
+++ b/arch/arm/include/asm/insn.h
@@ -13,18 +13,24 @@ arm_gen_nop(void)
}
unsigned long
-__arm_gen_branch(unsigned long pc, unsigned long addr, bool link);
+__arm_gen_branch(unsigned long pc, unsigned long addr, bool link, bool check);
static inline unsigned long
arm_gen_branch(unsigned long pc, unsigned long addr)
{
- return __arm_gen_branch(pc, addr, false);
+ return __arm_gen_branch(pc, addr, false, true);
}
static inline unsigned long
arm_gen_branch_link(unsigned long pc, unsigned long addr)
{
- return __arm_gen_branch(pc, addr, true);
+ return __arm_gen_branch(pc, addr, true, true);
+}
+
+static inline unsigned long
+arm_gen_branch_link_nocheck(unsigned long pc, unsigned long addr)
+{
+ return __arm_gen_branch(pc, addr, true, false);
}
#endif
diff --git a/arch/arm/kernel/ftrace.c b/arch/arm/kernel/ftrace.c
index fa867a57100f..63ea34edd222 100644
--- a/arch/arm/kernel/ftrace.c
+++ b/arch/arm/kernel/ftrace.c
@@ -70,20 +70,28 @@ int ftrace_arch_code_modify_post_process(void)
static unsigned long ftrace_call_replace(unsigned long pc, unsigned long addr)
{
- s32 offset = addr - pc;
- s32 blim = 0xfe000008;
- s32 flim = 0x02000004;
+ return arm_gen_branch_link(pc, addr);
+}
- if (IS_ENABLED(CONFIG_THUMB2_KERNEL)) {
- blim = 0xff000004;
- flim = 0x01000002;
- }
+static unsigned long
+ftrace_call_replace_mod(struct module *mod, unsigned long pc, unsigned long addr)
+{
+#ifdef CONFIG_ARM_MODULE_PLTS
+ unsigned long new;
- if (IS_ENABLED(CONFIG_ARM_MODULE_PLTS) &&
- (offset < blim || offset > flim))
- return 0;
+ if (likely(!mod))
+ return arm_gen_branch_link(pc, addr);
+ new = arm_gen_branch_link_nocheck(pc, addr);
+ if (!new) {
+ addr = get_module_plt(mod, pc, addr);
+ new = arm_gen_branch_link(pc, addr);
+ }
+
+ return new;
+#else
return arm_gen_branch_link(pc, addr);
+#endif
}
static int ftrace_modify_code(unsigned long pc, unsigned long old,
@@ -141,18 +149,7 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
old = ftrace_nop_replace(rec);
- new = ftrace_call_replace(ip, aaddr);
-
-#ifdef CONFIG_ARM_MODULE_PLTS
- if (!new) {
- struct module *mod = rec->arch.mod;
-
- if (mod) {
- aaddr = get_module_plt(mod, ip, aaddr);
- new = ftrace_call_replace(ip, aaddr);
- }
- }
-#endif
+ new = ftrace_call_replace_mod(ftrace_get_mod(&rec->arch), ip, aaddr);
return ftrace_modify_code(rec->ip, old, new, true);
}
@@ -183,23 +180,11 @@ int ftrace_make_nop(struct module *mod,
unsigned long new;
int ret;
-#ifdef CONFIG_ARM_MODULE_PLTS
/* mod is only supplied during module loading */
- if (!mod)
- mod = rec->arch.mod;
- else
- rec->arch.mod = mod;
-#endif
-
- old = ftrace_call_replace(ip, aaddr);
-
-#ifdef CONFIG_ARM_MODULE_PLTS
- if (!old && mod) {
- aaddr = get_module_plt(mod, ip, aaddr);
- old = ftrace_call_replace(ip, aaddr);
- }
-#endif
+ if (mod)
+ ftrace_set_mod(&rec->arch, mod);
+ old = ftrace_call_replace_mod(ftrace_get_mod(&rec->arch), ip, aaddr);
new = ftrace_nop_replace(rec);
ret = ftrace_modify_code(ip, old, new, true);
diff --git a/arch/arm/kernel/insn.c b/arch/arm/kernel/insn.c
index 2e844b70386b..37ec5734309e 100644
--- a/arch/arm/kernel/insn.c
+++ b/arch/arm/kernel/insn.c
@@ -4,7 +4,7 @@
#include <asm/opcodes.h>
static unsigned long
-__arm_gen_branch_thumb2(unsigned long pc, unsigned long addr, bool link)
+__arm_gen_branch_thumb2(unsigned long pc, unsigned long addr, bool link, bool check)
{
unsigned long s, j1, j2, i1, i2, imm10, imm11;
unsigned long first, second;
@@ -12,7 +12,7 @@ __arm_gen_branch_thumb2(unsigned long pc, unsigned long addr, bool link)
offset = (long)addr - (long)(pc + 4);
if (offset < -16777216 || offset > 16777214) {
- WARN_ON_ONCE(1);
+ WARN_ON_ONCE(check);
return 0;
}
@@ -34,7 +34,7 @@ __arm_gen_branch_thumb2(unsigned long pc, unsigned long addr, bool link)
}
static unsigned long
-__arm_gen_branch_arm(unsigned long pc, unsigned long addr, bool link)
+__arm_gen_branch_arm(unsigned long pc, unsigned long addr, bool link, bool check)
{
unsigned long opcode = 0xea000000;
long offset;
@@ -44,7 +44,7 @@ __arm_gen_branch_arm(unsigned long pc, unsigned long addr, bool link)
offset = (long)addr - (long)(pc + 8);
if (unlikely(offset < -33554432 || offset > 33554428)) {
- WARN_ON_ONCE(1);
+ WARN_ON_ONCE(check);
return 0;
}
@@ -54,10 +54,10 @@ __arm_gen_branch_arm(unsigned long pc, unsigned long addr, bool link)
}
unsigned long
-__arm_gen_branch(unsigned long pc, unsigned long addr, bool link)
+__arm_gen_branch(unsigned long pc, unsigned long addr, bool link, bool check)
{
if (IS_ENABLED(CONFIG_THUMB2_KERNEL))
- return __arm_gen_branch_thumb2(pc, addr, link);
+ return __arm_gen_branch_thumb2(pc, addr, link, check);
else
- return __arm_gen_branch_arm(pc, addr, link);
+ return __arm_gen_branch_arm(pc, addr, link, check);
}
View attachment "plt.patch" of type "text/x-diff" (5852 bytes)
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