[PATCH v2 1/1] ARM: kprobes: Explicitly reserve r7 for local variables

[Maria Yu]

Registers r7 is removed in clobber list, so compiler may choose r7 for
local variables usage, while r7 will be actually updated by the inline asm
code. This caused the runtime behavior wrong.
While those kind of reserved registers cannot be set to clobber list
because of error like "inline asm clobber list contains reserved
registers".
Explicitly reserve r7 by adding attribute no-omit-frame-pointer for needed
function, then in T32 asm code r7 is used as a frame pointer and is not
available for use as a general-purpose register.
Note that "no-omit-frame-pointer" will make the code size a little bigger
to store the stack frame pointer. So limited to needed functions can have
the less impact than the full source file.

Fixes: dd12e97f3c72 ("ARM: kprobes: treat R7 as the frame pointer register in Thumb2 builds")
Signed-off-by: Maria Yu <quic_aiquny@xxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
---
 arch/arm/probes/kprobes/actions-thumb.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/arm/probes/kprobes/actions-thumb.c b/arch/arm/probes/kprobes/actions-thumb.c
index 51624fc263fc..c2fdaf9f6dba 100644
--- a/arch/arm/probes/kprobes/actions-thumb.c
+++ b/arch/arm/probes/kprobes/actions-thumb.c
@@ -438,7 +438,7 @@ t16_simulate_branch(probes_opcode_t insn,
 	regs->ARM_pc = pc + (offset * 2);
 }
 
-static unsigned long __kprobes
+static unsigned long __kprobes __attribute__((optimize("no-omit-frame-pointer")))
 t16_emulate_loregs(probes_opcode_t insn,
 		   struct arch_probes_insn *asi, struct pt_regs *regs)
 {
@@ -521,7 +521,7 @@ t16_decode_hiregs(probes_opcode_t insn, struct arch_probes_insn *asi,
 	return INSN_GOOD;
 }
 
-static void __kprobes
+static void __kprobes __attribute__((optimize("no-omit-frame-pointer")))
 t16_emulate_push(probes_opcode_t insn,
 		struct arch_probes_insn *asi, struct pt_regs *regs)
 {
@@ -557,7 +557,7 @@ t16_decode_push(probes_opcode_t insn, struct arch_probes_insn *asi,
 	return INSN_GOOD;
 }
 
-static void __kprobes
+static void __kprobes __attribute__((optimize("no-omit-frame-pointer")))
 t16_emulate_pop_nopc(probes_opcode_t insn,
 		struct arch_probes_insn *asi, struct pt_regs *regs)
 {
@@ -576,7 +576,7 @@ t16_emulate_pop_nopc(probes_opcode_t insn,
 		);
 }
 
-static void __kprobes
+static void __kprobes __attribute__((optimize("no-omit-frame-pointer")))
 t16_emulate_pop_pc(probes_opcode_t insn,
 		struct arch_probes_insn *asi, struct pt_regs *regs)
 {

base-commit: 9bacdd8996c77c42ca004440be610692275ff9d0
-- 
2.17.1