[PATCH v4 31/31] ARM: entry: Straighten syscall returns
From: Linus Walleij <hidden>
Date: 2025-02-12 11:23:40
Also in:
lkml
Subsystem:
arm port, the rest · Maintainers:
Russell King, Linus Torvalds
Since ret_fast_syscall() is now only called in two spots in vector_swi, we can inline the function into vector_swi, and skip the separate call, placing the code from ret_fast_syscall at the end of vector_swi and one of them inside an ifdef that gets compiled out for !EABI. TODO: is the UNWIND(.fnstart/.cantunwind/.fnend) really needed on vector_swi after this change or can I just drop it? I do not understand unwind well enough :/ Signed-off-by: Linus Walleij <redacted> --- arch/arm/kernel/entry-common.S | 32 ++++++++++++++------------------ 1 file changed, 14 insertions(+), 18 deletions(-)
diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
index a5a0e757ab23d151485092a078af98966e039869..f9c38f5311851e299234997796cd78de06a5c531 100644
--- a/arch/arm/kernel/entry-common.S
+++ b/arch/arm/kernel/entry-common.S@@ -30,21 +30,6 @@ saved_pc .req lr .section .entry.text,"ax",%progbits .align 5 -/* - * As we will need to call out to some C functions, - * we save r0 first to avoid needing to save registers around each C function - * call. - */ -ret_fast_syscall: - UNWIND(.fnstart ) - UNWIND(.cantunwind ) - add sp, sp, #(S_R0 + S_OFF) -#ifdef CONFIG_GCC_PLUGIN_STACKLEAK - bl stackleak_erase_on_task_stack -#endif - restore_user_regs - UNWIND(.fnend ) -ENDPROC(ret_fast_syscall) /* * "slow" syscall return path. "why" tells us if this was a real syscall.
@@ -122,6 +107,8 @@ ENDPROC(vector_bhb_bpiall_swi) #endif .align 5 ENTRY(vector_swi) + UNWIND(.fnstart ) + UNWIND(.cantunwind ) #ifdef CONFIG_CPU_V7M v7m_exception_entry #else
@@ -210,9 +197,9 @@ ENTRY(vector_swi) mov r0, tbl mov r2, scno @ syscall number from r7 bl invoke_syscall - b ret_fast_syscall - #if defined(CONFIG_OABI_COMPAT) || !defined(CONFIG_AEABI) + b 9002 + /* * We failed to handle a fault trying to access the page * containing the swi instruction, but we're not really in a
@@ -225,8 +212,17 @@ ENTRY(vector_swi) sub lr, saved_pc, #4 str lr, [sp, #S_PC] get_thread_info tsk - b ret_fast_syscall +9002: + /* Exit !AEABI clause */ +#endif + + /* Return from syscall */ + add sp, sp, #(S_R0 + S_OFF) +#ifdef CONFIG_GCC_PLUGIN_STACKLEAK + bl stackleak_erase_on_task_stack #endif + restore_user_regs + UNWIND(.fnend ) ENDPROC(vector_swi) .ltorg
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