Hi Dylan, On Tue, Apr 28, 2026 at 06:36:38PM +0000, Dylan Hatch wrote: > From: Weinan Liu <[email protected]> > > DWARF CFI (Call Frame Information) specifies how to recover the return > address and callee-saved registers at each PC in a given function. > Compilers are able to generate the CFI annotations when they compile > the code to assembly language. For handcrafted assembly, we need to > annotate them by hand. > > Annotate minimal CFI to enable stacktracing using SFrame for kernel > exception entries through el1*_64_*() paths
I thought we were only consuming SFrame when unwinding an exeption boundary? We shouldn't be taking exceptions _from_ the entry assembly functions unless something has gone horribly wrong, and so I don't see why we'd need CFI entries for the entry assembly functions. Am I missing some reason we need CFI entries for the entry assembly functions? I strongly suspect it is not necessary to add these, and I'd prefer to omit them. > and irq entries through call_on_irq_stack() Needing some sort of unwind annotations for call_on_irq_stack() makes sense to me, but don't we need something for other assembly functions too? We can interrupt things like memset(); I assume we'll treat those as unreliable until annotated? Mark. > Signed-off-by: Weinan Liu <[email protected]> > Suggested-by: Jens Remus <[email protected]> > Reviewed-by: Jens Remus <[email protected]> > Signed-off-by: Dylan Hatch <[email protected]> > --- > arch/arm64/kernel/entry.S | 23 +++++++++++++++++++++++ > 1 file changed, 23 insertions(+) > > diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S > index f8018b5c1f9a..dc55b0b19cfa 100644 > --- a/arch/arm64/kernel/entry.S > +++ b/arch/arm64/kernel/entry.S > @@ -30,6 +30,12 @@ > #include <asm/asm-uaccess.h> > #include <asm/unistd.h> > > +/* > + * Do not generate .eh_frame. Only generate .debug_frame and optionally > + * .sframe (via assembler option --gsframe[-N]). > + */ > + .cfi_sections .debug_frame > + > .macro clear_gp_regs > .irp > n,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29 > mov x\n, xzr > @@ -575,7 +581,16 @@ SYM_CODE_START_LOCAL(el\el\ht\()_\regsize\()_\label) > .if \el == 0 > b ret_to_user > .else > + /* > + * Minimal DWARF CFI for unwinding across the call above. > + * Enable unwinding for el1*_64_*() path only. > + */ > + .cfi_startproc > + .cfi_def_cfa_offset PT_REGS_SIZE > + .cfi_offset 29, S_FP - PT_REGS_SIZE > + .cfi_offset 30, S_LR - PT_REGS_SIZE > b ret_to_kernel > + .cfi_endproc > .endif > SYM_CODE_END(el\el\ht\()_\regsize\()_\label) > .endm > @@ -872,6 +887,7 @@ NOKPROBE(ret_from_fork) > * Calls func(regs) using this CPU's irq stack and shadow irq stack. > */ > SYM_FUNC_START(call_on_irq_stack) > + .cfi_startproc > save_and_disable_daif x9 > #ifdef CONFIG_SHADOW_CALL_STACK > get_current_task x16 > @@ -882,6 +898,9 @@ SYM_FUNC_START(call_on_irq_stack) > /* Create a frame record to save our LR and SP (implicit in FP) */ > stp x29, x30, [sp, #-16]! > mov x29, sp > + .cfi_def_cfa 29, 16 > + .cfi_offset 29, -16 > + .cfi_offset 30, -8 > > ldr_this_cpu x16, irq_stack_ptr, x17 > > @@ -897,9 +916,13 @@ SYM_FUNC_START(call_on_irq_stack) > */ > mov sp, x29 > ldp x29, x30, [sp], #16 > + .cfi_restore 29 > + .cfi_restore 30 > + .cfi_def_cfa 31, 0 > scs_load_current > restore_irq x9 > ret > + .cfi_endproc > SYM_FUNC_END(call_on_irq_stack) > NOKPROBE(call_on_irq_stack) > > -- > 2.54.0.545.g6539524ca2-goog >
