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From: Jan Beulich <jbeulich@suse.com>
To: "Roger Pau Monné" <roger.pau@citrix.com>
Cc: "xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>,
	Andrew Cooper <andrew.cooper3@citrix.com>, Wei Liu <wl@xen.org>,
	George Dunlap <george.dunlap@citrix.com>
Subject: Re: [PATCH v5 2/8] x86: annotate entry points with type and size
Date: Fri, 19 Jan 2024 09:06:45 +0100	[thread overview]
Message-ID: <ceb07b66-8263-41b7-8c79-3cad89fc9400@suse.com> (raw)
In-Reply-To: <ZaljqHduUIvsdbqm@macbook>

On 18.01.2024 18:45, Roger Pau Monné wrote:
> 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.

It doesn't have to, but see the description for where I thought it would
make sense to newly introduce alignment; I simply didn't want to go too
far with such changes leading to generated code being altered. This (and
the other cases below) weren't in that group. Without ...

>>          ASSERT_CONTEXT_IS_XEN

... this I would be strongly inclined to switch ...

>>          jmp   restore_all_xen

... to

#define ret_from_intr restore_all_xen

anyway. And perhaps we ought to change the "#else" above to
"#elif !defined(NDEBUG)", at which point I'd say alignment isn't required
here at 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?

Oh, yes, very much so. Thanks for noticing. I'll do that in the later
patch, though.

>> @@ -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?

Well. If I used default alignment here, it would be the 1st stub only
which gains alignment. I'd view that as simply inconsistent. You'll
find there already is an ALIGN inside the .rept below. That covers
only certain cases, but intentionally so, I believe: it's only entry
points which shouldn't be reached anyway which get no alignment. So
yes, in this case I clearly think there wants to explicitly be no
alignment here.

Jan


  reply	other threads:[~2024-01-19  8:07 UTC|newest]

Thread overview: 100+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-04-12 10:25 [PATCH 0/2] x86: aid debug info generation in assembly files Jan Beulich
2022-04-12 10:27 ` [PATCH 1/2] x86: improve .debug_line contents for assembly sources Jan Beulich
2022-04-14 12:40   ` Roger Pau Monné
2022-04-14 12:52     ` Jan Beulich
2022-04-14 13:31       ` Roger Pau Monné
2022-04-14 13:36         ` Roger Pau Monné
2022-04-14 14:15         ` Jan Beulich
2022-04-14 16:02           ` Roger Pau Monné
2022-04-14 16:34             ` Jan Beulich
2022-04-26  9:26             ` Jan Beulich
2022-04-12 10:28 ` [PATCH 2/2] x86: annotate entry points with type and size Jan Beulich
2022-04-14 12:49   ` Andrew Cooper
2022-04-14 12:59     ` Jan Beulich
2022-06-23 11:47       ` Jan Beulich
2023-05-23 11:30 ` [PATCH v2 0/2] " Jan Beulich
2023-05-23 11:30   ` [PATCH v2 1/2] " Jan Beulich
2023-05-29 13:34     ` Roger Pau Monné
2023-05-30  8:06       ` Jan Beulich
2023-05-30 13:21         ` Roger Pau Monné
2023-05-30 14:23           ` Jan Beulich
2023-05-30 15:15             ` Roger Pau Monné
2023-05-23 11:31   ` [PATCH v2 2/2] x86: also mark assembler globals hidden Jan Beulich
2023-05-29 13:38     ` Roger Pau Monné
2023-07-10  8:50 ` [PATCH v3 0/8] annotate entry points with type and size Jan Beulich
2023-07-10  8:51   ` [PATCH v3 1/8] common: move a few macros out of xen/lib.h Jan Beulich
2023-07-18 15:40     ` Oleksii
2023-07-18 19:49     ` Shawn Anastasio
2023-07-19  6:28       ` Jan Beulich
2023-07-10  8:52   ` [PATCH v3 2/8] common: assembly entry point type/size annotations Jan Beulich
2023-07-10  9:28     ` Jan Beulich
2023-07-10  8:53   ` [PATCH v3 3/8] x86: annotate entry points with type and size Jan Beulich
2023-07-10  8:54   ` [PATCH v3 4/8] x86: also mark assembler globals hidden Jan Beulich
2023-07-10  8:55   ` [PATCH v3 5/8] Arm: annotate entry points with type and size Jan Beulich
2023-07-10  8:56   ` [PATCH v3 6/8] RISC-V: " Jan Beulich
2023-07-10  8:58     ` Jan Beulich
2023-07-26 15:28       ` Oleksii
2023-07-26 15:43         ` Jan Beulich
2023-07-26 16:55           ` Oleksii
2023-07-10  8:56   ` [PATCH v3 7/8] PPC: switch entry point annotations to common model Jan Beulich
2023-07-10  8:57   ` [PATCH v3 8/8] tools/binfile: switch to common annotations model Jan Beulich
2023-07-17 14:18   ` [PATCH v3 9/8] common: honor CONFIG_CC_SPLIT_SECTIONS also for assembly functions Jan Beulich
2023-07-18 12:28     ` Jan Beulich
2023-08-04  6:24 ` [PATCH v4 0/8] annotate entry points with type and size Jan Beulich
2023-08-04  6:26   ` [PATCH v4 1/8] common: assembly entry point type/size annotations Jan Beulich
2023-09-14 21:06     ` Julien Grall
2023-09-18 10:24       ` Jan Beulich
2023-09-18 10:34         ` Julien Grall
2023-09-18 10:51           ` Jan Beulich
2023-08-04  6:26   ` [PATCH v4 2/8] x86: annotate entry points with type and size Jan Beulich
2023-08-04  6:27   ` [PATCH v4 3/8] x86: also mark assembler globals hidden Jan Beulich
2023-08-04  6:28   ` [PATCH v4 4/8] Arm: annotate entry points with type and size Jan Beulich
2023-09-14 21:25     ` Julien Grall
2023-09-15  7:00       ` Jan Beulich
2023-08-04  6:29   ` [PATCH v4 5/8] RISC-V: " Jan Beulich
2023-08-04  6:30   ` [PATCH v4 5/8] PPC: switch entry point annotations to common model Jan Beulich
2023-08-04  6:30   ` [PATCH v4 6/8] tools/binfile: switch to common annotations model Jan Beulich
2023-09-14 21:30     ` Julien Grall
2023-08-04  6:31   ` [PATCH v4 8/8] common: honor CONFIG_CC_SPLIT_SECTIONS also for assembly functions Jan Beulich
2023-08-04  6:32   ` [PATCH v4 0/8] annotate entry points with type and size Jan Beulich
2024-01-15 14:30 ` [PATCH v5 " Jan Beulich
2024-01-15 14:34   ` [PATCH v5 1/8] common: assembly entry point type/size annotations Jan Beulich
2024-01-17 17:02     ` Roger Pau Monné
2024-01-18 15:48       ` Jan Beulich
2024-01-18 14:52     ` Roger Pau Monné
2024-01-18 16:00       ` Jan Beulich
2024-01-15 14:34   ` [PATCH v5 2/8] x86: annotate entry points with type and size Jan Beulich
2024-01-18 17:45     ` Roger Pau Monné
2024-01-19  8:06       ` Jan Beulich [this message]
2024-01-19  9:48     ` Roger Pau Monné
2024-01-15 14:35   ` [PATCH v5 3/8] x86: also mark assembler globals hidden Jan Beulich
2024-01-15 14:36   ` [PATCH v5 4/8] Arm: annotate entry points with type and size Jan Beulich
2024-01-22 13:22     ` Jan Beulich
2024-03-15 19:09       ` Julien Grall
2024-01-15 14:37   ` [PATCH v5 5/8] RISC-V: " Jan Beulich
2024-01-16 12:15     ` Oleksii
2024-01-15 14:38   ` [PATCH v5 6/8] PPC: switch entry point annotations to common model Jan Beulich
2024-01-22 13:20     ` Ping: " Jan Beulich
2024-01-23  3:00       ` Shawn Anastasio
2024-01-15 14:39   ` [PATCH v5 7/8] tools/binfile: switch to common annotations model Jan Beulich
2024-01-15 14:40   ` [PATCH v5 8/8] common: honor CONFIG_CC_SPLIT_SECTIONS also for assembly functions Jan Beulich
2024-01-19 10:36     ` Roger Pau Monné
2024-01-22 10:50       ` Jan Beulich
2024-01-22 17:40         ` Roger Pau Monné
2024-02-07 13:34 ` [PATCH v6 7/7] (mostly) x86: add/convert entry point annotations Jan Beulich
2024-02-07 13:35   ` [PATCH v6 0/7] " Jan Beulich
2024-02-07 13:36   ` [PATCH v6 1/7] common: honor CONFIG_CC_SPLIT_SECTIONS also for assembly functions Jan Beulich
2024-02-07 13:37   ` [PATCH v6 2/7] SVM: convert entry point annotations Jan Beulich
2024-02-07 13:48     ` Andrew Cooper
2024-02-07 13:37   ` [PATCH v6 3/7] VMX: " Jan Beulich
2024-02-07 13:55     ` Andrew Cooper
2024-02-07 14:25       ` Jan Beulich
2024-02-08 16:20         ` Jan Beulich
2024-02-07 13:37   ` [PATCH v6 4/7] x86/ACPI: annotate assembly functions with type and size Jan Beulich
2024-02-07 14:00     ` Andrew Cooper
2024-02-07 13:38   ` [PATCH v6 5/7] x86/kexec: convert entry point annotations Jan Beulich
2024-02-07 14:05     ` Andrew Cooper
2024-02-07 13:38   ` [PATCH v6 6/7] x86: convert misc assembly function annotations Jan Beulich
2024-02-07 14:11     ` Andrew Cooper
2024-02-07 13:39   ` [PATCH v6 7/7] x86: move ENTRY(), GLOBAL(), and ALIGN Jan Beulich
2024-02-07 14:27     ` Andrew Cooper

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