On 05/10/2013 04:07 AM, Tony Wu wrote:
Given a function, get_frame_info() analyzes its instructions
to figure out frame size and return address. get_frame_info()
works as follows:
1. analyze up to 128 instructions if the function size is unknown
2. search for 'addiu/daddiu sp,sp,-immed' for frame size
3. search for 'sw ra,offset(sp)' for return address
4. end search when it sees jr/jal/jalr
This leads to an issue when the given function is a sibling
call, example given as follows.
801ca110 <schedule>:
801ca110: 8f820000 lw v0,0(gp)
801ca114: 8c420000 lw v0,0(v0)
801ca118: 080726f0 j 801c9bc0 <__schedule>
801ca11c: 00000000 nop
801ca120 <io_schedule>:
801ca120: 27bdffe8 addiu sp,sp,-24
801ca124: 3c028022 lui v0,0x8022
801ca128: afbf0014 sw ra,20(sp)
In this case, get_frame_info() cannot properly detect schedule's
frame info, and eventually returns io_schedule's info instead.
This patch adds sibling call check by detecting out of range jump.
I think this is more complex than it needs to be. Also you already
handle the case of a sib call via a function pointer ....
Signed-off-by: Tony Wu <tung7970@xxxxxxxxx>
---
arch/mips/kernel/process.c | 22 ++++++++++++++++++++++
1 file changed, 22 insertions(+)
diff --git a/arch/mips/kernel/process.c b/arch/mips/kernel/process.c
index cfc742d..a794eb5 100644
--- a/arch/mips/kernel/process.c
+++ b/arch/mips/kernel/process.c
@@ -223,6 +223,9 @@ struct mips_frame_info {
int pc_offset;
};
+#define J_TARGET(pc,target) \
+ (((unsigned long)(pc) & 0xf0000000) | ((target) << 2))
+
static inline int is_ra_save_ins(union mips_instruction *ip)
{
/* sw / sd $ra, offset($sp) */
@@ -250,11 +253,25 @@ static inline int is_sp_move_ins(union mips_instruction *ip)
return 0;
}
+static inline int is_sibling_j_ins(union mips_instruction *ip,
+ unsigned long func_begin, unsigned long func_end)
+{
+ if (ip->j_format.opcode == j_op) {
+ unsigned long addr;
+
+ addr = J_TARGET(ip, ip->j_format.target);
+ if (addr < func_begin || addr > func_end)
+ return 1;
+ }
+ return 0;
+}
+
static int get_frame_info(struct mips_frame_info *info)
{
union mips_instruction *ip = info->func;
unsigned max_insns = info->func_size / sizeof(union mips_instruction);
unsigned i;
+ unsigned long func_begin, func_end;
info->pc_offset = -1;
info->frame_size = 0;
@@ -266,10 +283,15 @@ static int get_frame_info(struct mips_frame_info *info)
max_insns = 128U; /* unknown function size */
max_insns = min(128U, max_insns);
+ func_begin = (unsigned long) info->func;
+ func_end = func_begin + max_insns * sizeof(union mips_instruction);
+
for (i = 0; i < max_insns; i++, ip++) {
if (is_jal_jalr_jr_ins(ip))
break;
... here. So why not just add an unconditional J to the list detected,
and get rid of all the rest of the patch?
+ if (is_sibling_j_ins(ip, func_begin, func_end))
+ break;
if (!info->frame_size) {
if (is_sp_move_ins(ip))
info->frame_size = - ip->i_format.simmediate;
