It was previously noted that CALL/BUG is a weird combination, but there is good reason to use this pattern.
Introduce an explicit tailcall macro make it clearer in context. No functional change. Reported-by: Jan Beulich <[email protected]> Signed-off-by: Andrew Cooper <[email protected]> --- CC: Jan Beulich <[email protected]> CC: Roger Pau Monné <[email protected]> CC: Wei Liu <[email protected]> It would be nicer if tailcall was shorter, but that loses clarity. RISC-V has 'tail' as an alias for 'b', but that looses the call aspect, and tcall isn't sufficiently recognisable as tailcall IMO. --- xen/arch/x86/boot/x86_64.S | 6 ++---- xen/arch/x86/include/asm/asm-defns.h | 9 +++++++++ xen/arch/x86/x86_64/entry.S | 12 ++++-------- 3 files changed, 15 insertions(+), 12 deletions(-) diff --git a/xen/arch/x86/boot/x86_64.S b/xen/arch/x86/boot/x86_64.S index 5d12937a0e40..04bb62ae8680 100644 --- a/xen/arch/x86/boot/x86_64.S +++ b/xen/arch/x86/boot/x86_64.S @@ -74,14 +74,12 @@ ENTRY(__high_start) .L_ap_cet_done: #endif /* CONFIG_XEN_SHSTK || CONFIG_XEN_IBT */ - call start_secondary - BUG /* start_secondary() shouldn't return. */ + tailcall start_secondary .L_bsp: /* Pass off the Multiboot info structure to C land (if applicable). */ mov multiboot_ptr(%rip),%edi - call __start_xen - BUG /* __start_xen() shouldn't return. */ + tailcall __start_xen .section .data.page_aligned, "aw", @progbits .align PAGE_SIZE, 0 diff --git a/xen/arch/x86/include/asm/asm-defns.h b/xen/arch/x86/include/asm/asm-defns.h index 8bd9007731d5..9a7073ced5be 100644 --- a/xen/arch/x86/include/asm/asm-defns.h +++ b/xen/arch/x86/include/asm/asm-defns.h @@ -20,6 +20,15 @@ .byte 0x0f, 0x01, 0xdd .endm +/* + * Call a noreturn function. This could be JMP, but CALL results in a more + * helpful backtrace. BUG is to catch functions which do decide to return... + */ +.macro tailcall fn:req + call \fn + BUG /* Shouldn't return */ +.endm + .macro INDIRECT_BRANCH insn:req arg:req /* * Create an indirect branch. insn is one of call/jmp, arg is a single diff --git a/xen/arch/x86/x86_64/entry.S b/xen/arch/x86/x86_64/entry.S index 8b77d7113bbf..bca1500e2b45 100644 --- a/xen/arch/x86/x86_64/entry.S +++ b/xen/arch/x86/x86_64/entry.S @@ -824,8 +824,7 @@ handle_exception_saved: DISPATCH(X86_EXC_CP, do_entry_CP) #undef DISPATCH - call do_unhandled_trap - BUG /* do_unhandled_trap() shouldn't return. */ + tailcall do_unhandled_trap .L_exn_dispatch_done: mov %r15, STACK_CPUINFO_FIELD(xen_cr3)(%r14) @@ -880,8 +879,7 @@ exception_with_ints_disabled: FATAL_exception_with_ints_disabled: xorl %esi,%esi movq %rsp,%rdi - call fatal_trap - BUG /* fatal_trap() shouldn't return. */ + tailcall fatal_trap ENTRY(divide_error) ENDBR64 @@ -989,8 +987,7 @@ ENTRY(double_fault) .Ldblf_cr3_okay: movq %rsp,%rdi - call do_double_fault - BUG /* do_double_fault() shouldn't return. */ + tailcall do_double_fault ENTRY(nmi) ENDBR64 @@ -1085,8 +1082,7 @@ handle_ist_exception: DISPATCH(X86_EXC_MC, do_machine_check) #undef DISPATCH - call do_unhandled_trap - BUG /* do_unhandled_trap() shouldn't return. */ + tailcall do_unhandled_trap .L_ist_dispatch_done: mov %r15, STACK_CPUINFO_FIELD(xen_cr3)(%r14) base-commit: f51e5d8eae8ece77a949571f39ee49904f3129aa -- 2.30.2
