On 05/27/2020 11:19 PM, Mark Rutland wrote:
On Wed, May 27, 2020 at 09:33:00AM +0800, Jiping Ma wrote:
On 05/26/2020 06:26 PM, Mark Rutland wrote:
On Mon, May 11, 2020 at 10:52:07AM +0800, Jiping Ma wrote:
Modified the patch subject and the change description.
PC value is get from regs[15] in REGS_ABI_32 mode, but correct PC
is regs->pc(regs[PERF_REG_ARM64_PC]) in arm64 kernel, which caused
that perf can not parser the backtrace of app with dwarf mode in the
32bit system and 64bit kernel.
Signed-off-by: Jiping Ma <jiping....@windriver.com>
Thanks for this.
---
arch/arm64/kernel/perf_regs.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/arch/arm64/kernel/perf_regs.c b/arch/arm64/kernel/perf_regs.c
index 0bbac61..0ef2880 100644
--- a/arch/arm64/kernel/perf_regs.c
+++ b/arch/arm64/kernel/perf_regs.c
@@ -32,6 +32,10 @@ u64 perf_reg_value(struct pt_regs *regs, int idx)
if ((u32)idx == PERF_REG_ARM64_PC)
return regs->pc;
+ if (perf_reg_abi(current) == PERF_SAMPLE_REGS_ABI_32
+ && idx == 15)
+ return regs->pc;
I think there are some more issues here, and we may need a more
substantial rework. For a compat thread, we always expose
PERF_SAMPLE_REGS_ABI_32 via per_reg_abi(), but for some reason
perf_reg_value() also munges the compat SP/LR into their ARM64
equivalents, which don't exist in the 32-bit sample ABI. We also don't
zero the regs that don't exist in 32-bit (including the aliasing PC).
I reckon what we should do is have seperate functions for the two ABIs,
to ensure we don't conflate them, e.g.
u64 perf_reg_value_abi32(struct pt_regs *regs, int idx)
{
if ((u32)idx > PERF_REG_ARM32_PC)
return 0;
if (idx == PERF_REG_ARM32_PC)
return regs->pc;
/*
* Compat SP and LR already in-place
*/
return regs->regs[idx];
}
u64 perf_reg_value_abi64(struct pt_regs *regs, int idx)
{
if ((u32)idx > PERF_REG_ARM64_MAX)
return 0;
if ((u32)idx == PERF_REG_ARM64_SP)
return regs->sp;
if ((u32)idx == PERF_REG_ARM64_PC)
return regs->pc;
reutrn regs->regs[idx];
}
u64 perf_reg_value(struct pt_regs *regs, int idx)
{
if (compat_user_mode(regs))
return perf_reg_value_abi32(regs, idx);
else
return perf_reg_value_abi64(regs, idx);
}
This modification can not fix our issue, we need
perf_reg_abi(current) == PERF_SAMPLE_REGS_ABI_32 to judge if it is 32-bit
task or not,
then return the correct PC value.
I must be missing something here.
The core code perf_reg_abi(task) is called with the task being sampled,
and the regs are from the task being sampled. For a userspace sample for
a compat task, compat_user_mode(regs) should be equivalent to the
is_compat_thread(task_thread_info(task)) check.
What am I missing?
This issue caused by PC value is not correct. regs are sampled in
function perf_output_sample_regs, that call perf_reg_value(regs, bit) to
get PC value.
PC value is regs[15] in perf_reg_value() function. it should be regs[32].
perf_output_sample_regs(struct perf_output_handle *handle,
struct pt_regs *regs, u64 mask)
{
int bit;
DECLARE_BITMAP(_mask, 64);
bitmap_from_u64(_mask, mask);
for_each_set_bit(bit, _mask, sizeof(mask) * BITS_PER_BYTE) {
u64 val;
val = perf_reg_value(regs, bit);
perf_output_put(handle, val);
}
}
Thanks,
Mark.
