[PATCH] riscv: Fix 32-bit call_on_irq_stack() frame pointer ABI

* [PATCH] riscv: Fix 32-bit call_on_irq_stack() frame pointer ABI
@ 2026-06-24 11:31 ` Rui Qi
  0 siblings, 0 replies; 4+ messages in thread
From: Rui Qi @ 2026-06-24 11:31 UTC (permalink / raw)
  To: palmer, pjw, aou, alex, conor
  Cc: linux-riscv, linux-kernel, samuel.holland, namcao, Rui Qi

From: Samuel Holland <samuel.holland@sifive.com>

call_on_irq_stack() uses struct member offsets to set up its link in the
frame record list. On riscv32, struct stackframe is the wrong size to
maintain stack pointer alignment, so STACKFRAME_SIZE_ON_STACK includes
padding. However, the ABI requires the frame record to be placed
immediately below the address stored in s0, so the padding must come
before the struct members.

Fix the layout by making STACKFRAME_FP and STACKFRAME_RA the negative
offsets from s0, instead of the positive offsets from sp.

Fixes: 82982fdd5133 ("riscv: Deduplicate IRQ stack switching")
Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
Signed-off-by: Rui Qi <qirui.001@bytedance.com>
Link: https://lore.kernel.org/all/20240530001733.1407654-2-samuel.holland@sifive.com/
This is a resubmission of Samuel Holland's patch [1] which was
posted in May 2024 but never merged. The bug still exists in the
current tree.

[1] https://lore.kernel.org/all/20240530001733.1407654-2-samuel.holland@sifive.com/
---
 arch/riscv/kernel/asm-offsets.c | 4 ++--
 arch/riscv/kernel/entry.S       | 8 ++++----
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/arch/riscv/kernel/asm-offsets.c b/arch/riscv/kernel/asm-offsets.c
index af827448a609..a75f0cfea1e9 100644
--- a/arch/riscv/kernel/asm-offsets.c
+++ b/arch/riscv/kernel/asm-offsets.c
@@ -501,8 +501,8 @@ void asm_offsets(void)
 	OFFSET(SBI_HART_BOOT_STACK_PTR_OFFSET, sbi_hart_boot_data, stack_ptr);
 
 	DEFINE(STACKFRAME_SIZE_ON_STACK, ALIGN(sizeof(struct stackframe), STACK_ALIGN));
-	OFFSET(STACKFRAME_FP, stackframe, fp);
-	OFFSET(STACKFRAME_RA, stackframe, ra);
+	DEFINE(STACKFRAME_FP, offsetof(struct stackframe, fp) - sizeof(struct stackframe));
+	DEFINE(STACKFRAME_RA, offsetof(struct stackframe, ra) - sizeof(struct stackframe));
 #ifdef CONFIG_FUNCTION_TRACER
 	DEFINE(FTRACE_OPS_FUNC,		offsetof(struct ftrace_ops, func));
 #ifdef CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
index c6988983cdf7..08df724e13b9 100644
--- a/arch/riscv/kernel/entry.S
+++ b/arch/riscv/kernel/entry.S
@@ -386,8 +386,8 @@ SYM_CODE_END(ret_from_fork_user_asm)
 SYM_FUNC_START(call_on_irq_stack)
 	/* Create a frame record to save ra and s0 (fp) */
 	addi	sp, sp, -STACKFRAME_SIZE_ON_STACK
-	REG_S	ra, STACKFRAME_RA(sp)
-	REG_S	s0, STACKFRAME_FP(sp)
+	REG_S	ra, (STACKFRAME_SIZE_ON_STACK + STACKFRAME_RA)(sp)
+	REG_S	s0, (STACKFRAME_SIZE_ON_STACK + STACKFRAME_FP)(sp)
 	addi	s0, sp, STACKFRAME_SIZE_ON_STACK
 
 	/* Switch to the per-CPU shadow call stack */
@@ -405,8 +405,8 @@ SYM_FUNC_START(call_on_irq_stack)
 
 	/* Switch back to the thread stack and restore ra and s0 */
 	addi	sp, s0, -STACKFRAME_SIZE_ON_STACK
-	REG_L	ra, STACKFRAME_RA(sp)
-	REG_L	s0, STACKFRAME_FP(sp)
+	REG_L	ra, (STACKFRAME_SIZE_ON_STACK + STACKFRAME_RA)(sp)
+	REG_L	s0, (STACKFRAME_SIZE_ON_STACK + STACKFRAME_FP)(sp)
 	addi	sp, sp, STACKFRAME_SIZE_ON_STACK
 
 	ret
-- 
2.20.1

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