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LoongArch: Refactor register restoration in ftrace_common_return

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Refactor the register restoration sequence in the ftrace_common_return
function to clearly distinguish between the logic of normal returns and
direct call returns in function tracing scenarios. The logic is as
follows:

1. In the case of a normal return, the execution flow returns to the
traced function, and ftrace must ensure that the register data is
consistent with the state when the function was entered.

ra = parent return address; t0 = traced function return address.

2. In the case of a direct call return, the execution flow jumps to the
custom trampoline function, and ftrace must ensure that the register
data is consistent with the state when ftrace was entered.

ra = traced function return address; t0 = parent return address.

Cc: stable@vger.kernel.org
Fixes: 9cdc3b6a29 ("LoongArch: ftrace: Add direct call support")
Signed-off-by: Chenghao Duan <duanchenghao@kylinos.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
This commit is contained in:
Chenghao Duan 2025-12-31 15:19:20 +08:00 • committed by Huacai Chen
parent 9bdc1ab5e4
commit 45cb47c628
1 changed files with 10 additions and 4 deletions
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14
arch/loongarch/kernel/mcount_dyn.S
View file

@ -94,7 +94,6 @@ SYM_INNER_LABEL(ftrace_graph_call, SYM_L_GLOBAL)
* at the callsite, so there is no need to restore the T series regs.
*/
ftrace_common_return:
PTR_L ra, sp, PT_R1
PTR_L a0, sp, PT_R4
PTR_L a1, sp, PT_R5
PTR_L a2, sp, PT_R6
@ -104,12 +103,17 @@ ftrace_common_return:
PTR_L a6, sp, PT_R10
PTR_L a7, sp, PT_R11
PTR_L fp, sp, PT_R22
PTR_L t0, sp, PT_ERA
PTR_L t1, sp, PT_R13
PTR_ADDI sp, sp, PT_SIZE
bnez t1, .Ldirect
PTR_L ra, sp, PT_R1
PTR_L t0, sp, PT_ERA
PTR_ADDI sp, sp, PT_SIZE
jr t0
.Ldirect:
PTR_L t0, sp, PT_R1
PTR_L ra, sp, PT_ERA
PTR_ADDI sp, sp, PT_SIZE
jr t1
SYM_CODE_END(ftrace_common)
@ -161,6 +165,8 @@ SYM_CODE_END(return_to_handler)
#ifdef CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
SYM_CODE_START(ftrace_stub_direct_tramp)
UNWIND_HINT_UNDEFINED
jr t0
move t1, ra
move ra, t0
jr t1
SYM_CODE_END(ftrace_stub_direct_tramp)
#endif /* CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS */