Re: [PATCH v5 2/8] x86: annotate entry points with type and size

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Mon, Jan 15, 2024 at 03:34:56PM +0100, Jan Beulich wrote:
> @@ -625,7 +627,7 @@ ENTRY(dom_crash_sync_extable)
>  
>  /* No special register assumptions. */
>  #ifdef CONFIG_PV
> -ENTRY(continue_pv_domain)
> +FUNC(continue_pv_domain)
>          ENDBR64
>          call  check_wakeup_from_wait
>  ret_from_intr:
> @@ -640,26 +642,28 @@ ret_from_intr:
>  #else
>          jmp   test_all_events
>  #endif
> +END(continue_pv_domain)
>  #else
> -ret_from_intr:
> +FUNC_LOCAL(ret_from_intr, 0)

Why does this need to have an alignment of 0? There's no fallthrough
of previous code AFAICT.

>          ASSERT_CONTEXT_IS_XEN
>          jmp   restore_all_xen
> +END(ret_from_intr)
>  #endif
>  
>          .section .init.text, "ax", @progbits
> -ENTRY(early_page_fault)
> +FUNC(early_page_fault)
>          ENDBR64
>          movl  $X86_EXC_PF, 4(%rsp)
>          SAVE_ALL
>          movq  %rsp, %rdi
>          call  do_early_page_fault
>          jmp   restore_all_xen
> +END(early_page_fault)
>  
>          .section .text.entry, "ax", @progbits
>  
> -        ALIGN
>  /* %r12=ist_exit */
> -restore_all_xen:
> +FUNC_LOCAL(restore_all_xen)
>  
>  #ifdef CONFIG_DEBUG
>          mov   %rsp, %rdi
> @@ -683,8 +687,9 @@ UNLIKELY_END(exit_cr3)
>  
>          RESTORE_ALL adj=8
>          iretq
> +END(restore_all_xen)
>  
> -ENTRY(common_interrupt)
> +FUNC(common_interrupt)
>          ALTERNATIVE "", clac, X86_FEATURE_XEN_SMAP
>          SAVE_ALL
>  
> @@ -713,12 +718,14 @@ ENTRY(common_interrupt)
>          mov   %r15, STACK_CPUINFO_FIELD(xen_cr3)(%r14)
>          mov   %bl, STACK_CPUINFO_FIELD(use_pv_cr3)(%r14)
>          jmp ret_from_intr
> +END(common_interrupt)
>  
> -ENTRY(entry_PF)
> +FUNC(entry_PF)
>          ENDBR64
>          movl  $X86_EXC_PF, 4(%rsp)
> +END(entry_PF)
>  /* No special register assumptions. */
> -GLOBAL(handle_exception)
> +FUNC(handle_exception, 0)

Given patch 8/8 that enables support for placing FUNC() into separate
sections, the fallthrough arrangement here with entry_PF is no longer
guaranteed, as the linker could re-order the sections and thus
entry_PF could fallthrough into another text section?

IOW: entry_PF needs a "jmp handle_exception", and then
handle_exception itself can be padded as required by the default
alignment?

>          ALTERNATIVE "", clac, X86_FEATURE_XEN_SMAP
>          SAVE_ALL
>  
> @@ -886,92 +893,108 @@ FATAL_exception_with_ints_disabled:
>          xorl  %esi,%esi
>          movq  %rsp,%rdi
>          tailcall fatal_trap
> +END(handle_exception)
>  
> -ENTRY(entry_DE)
> +FUNC(entry_DE)
>          ENDBR64
>          pushq $0
>          movl  $X86_EXC_DE, 4(%rsp)
>          jmp   handle_exception
> +END(entry_DE)
>  
> -ENTRY(entry_MF)
> +FUNC(entry_MF)
>          ENDBR64
>          pushq $0
>          movl  $X86_EXC_MF, 4(%rsp)
>          jmp   handle_exception
> +END(entry_MF)
>  
> -ENTRY(entry_XM)
> +FUNC(entry_XM)
>          ENDBR64
>          pushq $0
>          movl  $X86_EXC_XM, 4(%rsp)
>          jmp   handle_exception
> +END(entry_XM)
>  
> -ENTRY(entry_NM)
> +FUNC(entry_NM)
>          ENDBR64
>          pushq $0
>          movl  $X86_EXC_NM, 4(%rsp)
>          jmp   handle_exception
> +END(entry_NM)
>  
> -ENTRY(entry_DB)
> +FUNC(entry_DB)
>          ENDBR64
>          pushq $0
>          movl  $X86_EXC_DB, 4(%rsp)
>          jmp   handle_ist_exception
> +END(entry_DB)
>  
> -ENTRY(entry_BP)
> +FUNC(entry_BP)
>          ENDBR64
>          pushq $0
>          movl  $X86_EXC_BP, 4(%rsp)
>          jmp   handle_exception
> +END(entry_BP)
>  
> -ENTRY(entry_OF)
> +FUNC(entry_OF)
>          ENDBR64
>          pushq $0
>          movl  $X86_EXC_OF, 4(%rsp)
>          jmp   handle_exception
> +END(entry_OF)
>  
> -ENTRY(entry_BR)
> +FUNC(entry_BR)
>          ENDBR64
>          pushq $0
>          movl  $X86_EXC_BR, 4(%rsp)
>          jmp   handle_exception
> +END(entry_BR)
>  
> -ENTRY(entry_UD)
> +FUNC(entry_UD)
>          ENDBR64
>          pushq $0
>          movl  $X86_EXC_UD, 4(%rsp)
>          jmp   handle_exception
> +END(entry_UD)
>  
> -ENTRY(entry_TS)
> +FUNC(entry_TS)
>          ENDBR64
>          movl  $X86_EXC_TS, 4(%rsp)
>          jmp   handle_exception
> +END(entry_TS)
>  
> -ENTRY(entry_NP)
> +FUNC(entry_NP)
>          ENDBR64
>          movl  $X86_EXC_NP, 4(%rsp)
>          jmp   handle_exception
> +END(entry_NP)
>  
> -ENTRY(entry_SS)
> +FUNC(entry_SS)
>          ENDBR64
>          movl  $X86_EXC_SS, 4(%rsp)
>          jmp   handle_exception
> +END(entry_SS)
>  
> -ENTRY(entry_GP)
> +FUNC(entry_GP)
>          ENDBR64
>          movl  $X86_EXC_GP, 4(%rsp)
>          jmp   handle_exception
> +END(entry_GP)
>  
> -ENTRY(entry_AC)
> +FUNC(entry_AC)
>          ENDBR64
>          movl  $X86_EXC_AC, 4(%rsp)
>          jmp   handle_exception
> +END(entry_AC)
>  
> -ENTRY(entry_CP)
> +FUNC(entry_CP)
>          ENDBR64
>          movl  $X86_EXC_CP, 4(%rsp)
>          jmp   handle_exception
> +END(entry_CP)
>  
> -ENTRY(entry_DF)
> +FUNC(entry_DF)
>          ENDBR64
>          movl  $X86_EXC_DF, 4(%rsp)
>          /* Set AC to reduce chance of further SMAP faults */
> @@ -994,8 +1017,9 @@ ENTRY(entry_DF)
>  
>          movq  %rsp,%rdi
>          tailcall do_double_fault
> +END(entry_DF)
>  
> -ENTRY(entry_NMI)
> +FUNC(entry_NMI)
>          ENDBR64
>          pushq $0
>          movl  $X86_EXC_NMI, 4(%rsp)
> @@ -1126,21 +1150,24 @@ handle_ist_exception:
>          ASSERT_CONTEXT_IS_XEN
>          jmp   restore_all_xen
>  #endif
> +END(entry_NMI)
>  
> -ENTRY(entry_MC)
> +FUNC(entry_MC)
>          ENDBR64
>          pushq $0
>          movl  $X86_EXC_MC, 4(%rsp)
>          jmp   handle_ist_exception
> +END(entry_MC)
>  
>  /* No op trap handler.  Required for kexec crash path. */
> -GLOBAL(trap_nop)
> +FUNC(trap_nop, 0)

Could this use the default alignment?

>          ENDBR64
>          iretq
> +END(trap_nop)
>  
>  /* Table of automatically generated entry points.  One per vector. */
>          .pushsection .init.rodata, "a", @progbits
> -GLOBAL(autogen_entrypoints)
> +DATA(autogen_entrypoints, 8)
>          /* pop into the .init.rodata section and record an entry point. */
>          .macro entrypoint ent
>          .pushsection .init.rodata, "a", @progbits
> @@ -1149,7 +1176,7 @@ GLOBAL(autogen_entrypoints)
>          .endm
>  
>          .popsection
> -autogen_stubs: /* Automatically generated stubs. */
> +FUNC_LOCAL(autogen_stubs, 0) /* Automatically generated stubs. */

Won't it be good to align the stubs?  As that's possible to make them
faster?

Thanks, Roger.