[PATCH] gas: update csect alignment for PPC prefixed instructions on XCOFF

[PATCH] gas: update csect alignment for PPC prefixed instructions on XCOFF

[CHIGOT, CLEMENT]

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Power10 prefixed instructions must not cross 64-byte boundaries.
This is already handled.
However, on XCOFF, the csect must be updated to match the new
alignment.

gas/ChangeLog:
2021-06-22  Clément Chigot  <clement.chigot@atos.net>

        * config/tc-ppc.c (md_assemble): Update ppc_current_csect
        alignment when finding prefixed instructions.




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[-- Type: text/x-patch; name="0001-gas-update-csect-alignment-for-PPC-prefixed-instruct.patch", Size: 1324 bytes --]

From d4b4c74e9794dfc77d62f39ca16b6f8d1076c7c6 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Cl=C3=A9ment=20Chigot?= <clement.chigot@atos.net>
Date: Tue, 22 Jun 2021 10:15:06 +0200
Subject: [PATCH] gas: update csect alignment for PPC prefixed instructions on
 XCOFF
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Power10 prefixed instructions must not cross 64-byte boundaries.
This is already handled.
However, on XCOFF, the csect must be updated to match the new
alignment.

gas/ChangeLog:
2021-06-22  Clément Chigot  <clement.chigot@atos.net>

	* config/tc-ppc.c (md_assemble): Update ppc_current_csect
	alignment when finding prefixed instructions.
---
 gas/config/tc-ppc.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/gas/config/tc-ppc.c b/gas/config/tc-ppc.c
index ad85d3863b0..1f49db34659 100644
--- a/gas/config/tc-ppc.c
+++ b/gas/config/tc-ppc.c
@@ -4039,6 +4039,10 @@ md_assemble (char *str)
 	 boundaries.  */
       frag_align_code (6, 4);
       record_alignment (now_seg, 6);
+#ifdef OBJ_XCOFF
+      /* Update alignment of the containing csect.  */
+      symbol_get_tc (ppc_current_csect)->align = 6;
+#endif
 
       /* Update "dot" in any expressions used by this instruction, and
 	 a label attached to the instruction.  By "attached" we mean
-- 
2.25.1

Re: [PATCH] gas: update csect alignment for PPC prefixed instructions on XCOFF

[Alan Modra]

On Tue, Jun 22, 2021 at 11:19:30AM +0000, CHIGOT, CLEMENT via Binutils wrote:
> --- a/gas/config/tc-ppc.c
> +++ b/gas/config/tc-ppc.c
> @@ -4039,6 +4039,10 @@ md_assemble (char *str)
>  	 boundaries.  */
>        frag_align_code (6, 4);
>        record_alignment (now_seg, 6);
> +#ifdef OBJ_XCOFF
> +      /* Update alignment of the containing csect.  */
> +      symbol_get_tc (ppc_current_csect)->align = 6;
> +#endif

Is there a possibility that this might decrease alignment?  If so, you
should write:

     if (symbol_get_tc (ppc_current_csect)->align < 6)
       symbol_get_tc (ppc_current_csect)->align = 6;

-- 
Alan Modra
Australia Development Lab, IBM

Re: [PATCH] gas: update csect alignment for PPC prefixed instructions on XCOFF

[CHIGOT, CLEMENT]

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>> +++ b/gas/config/tc-ppc.c
>> @@ -4039,6 +4039,10 @@ md_assemble (char *str)
>>         boundaries.  */
>>        frag_align_code (6, 4);
>>        record_alignment (now_seg, 6);
>> +#ifdef OBJ_XCOFF
>> +      /* Update alignment of the containing csect.  */
>> +      symbol_get_tc (ppc_current_csect)->align = 6;
>> +#endif
>
> Is there a possibility that this might decrease alignment?  If so, you
> should write:
> 
>     if (symbol_get_tc (ppc_current_csect)->align < 6)
>        symbol_get_tc (ppc_current_csect)->align = 6;

Any value can be passed for the alignment of csect. Thus, it might be
possible but I doubt it will ever happen. 
Anyway I've updated the patch.

Clément


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From 12a9a4189bf294e88eec689a56334659138a9cec Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Cl=C3=A9ment=20Chigot?= <clement.chigot@atos.net>
Date: Tue, 22 Jun 2021 10:15:06 +0200
Subject: [PATCH] gas: update csect alignment for PPC prefixed instructions on
 XCOFF
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Power10 prefixed instructions must not cross 64-byte boundaries.
This is already handled.
However, on XCOFF, the csect must be updated to match the new
alignment.

gas/ChangeLog:
2021-06-22  Clément Chigot  <clement.chigot@atos.net>

	* config/tc-ppc.c (md_assemble): Update ppc_current_csect
	alignment when finding prefixed instructions.
---
 gas/config/tc-ppc.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/gas/config/tc-ppc.c b/gas/config/tc-ppc.c
index ad85d3863b0..80818e9c943 100644
--- a/gas/config/tc-ppc.c
+++ b/gas/config/tc-ppc.c
@@ -4039,6 +4039,11 @@ md_assemble (char *str)
 	 boundaries.  */
       frag_align_code (6, 4);
       record_alignment (now_seg, 6);
+#ifdef OBJ_XCOFF
+      /* Update alignment of the containing csect.  */
+      if (symbol_get_tc (ppc_current_csect)->align < 6)
+	symbol_get_tc (ppc_current_csect)->align = 6;
+#endif
 
       /* Update "dot" in any expressions used by this instruction, and
 	 a label attached to the instruction.  By "attached" we mean
-- 
2.25.1

Re: [PATCH] gas: update csect alignment for PPC prefixed instructions on XCOFF

[Alan Modra]

On Wed, Jun 23, 2021 at 06:49:04AM +0000, CHIGOT, CLEMENT wrote:
> >> +++ b/gas/config/tc-ppc.c
> >> @@ -4039,6 +4039,10 @@ md_assemble (char *str)
> >>         boundaries.  */
> >>        frag_align_code (6, 4);
> >>        record_alignment (now_seg, 6);
> >> +#ifdef OBJ_XCOFF
> >> +      /* Update alignment of the containing csect.  */
> >> +      symbol_get_tc (ppc_current_csect)->align = 6;
> >> +#endif
> >
> > Is there a possibility that this might decrease alignment?  If so, you
> > should write:
> > 
> >     if (symbol_get_tc (ppc_current_csect)->align < 6)
> >        symbol_get_tc (ppc_current_csect)->align = 6;
> 
> Any value can be passed for the alignment of csect. Thus, it might be
> possible but I doubt it will ever happen. 
> Anyway I've updated the patch.

OK, I've committed the patch for you.

-- 
Alan Modra
Australia Development Lab, IBM

Re: [PATCH] gas: update csect alignment for PPC prefixed instructions on XCOFF

[David Edelsohn]

>>> +++ b/gas/config/tc-ppc.c
>>> @@ -4039,6 +4039,10 @@ md_assemble (char *str)
>>>         boundaries.  */
>>>        frag_align_code (6, 4);
>>>        record_alignment (now_seg, 6);
>>> +#ifdef OBJ_XCOFF
>>> +      /* Update alignment of the containing csect.  */
>>> +      symbol_get_tc (ppc_current_csect)->align = 6;
>>> +#endif
>>
>> Is there a possibility that this might decrease alignment?  If so, you
>> should write:
>>
>>     if (symbol_get_tc (ppc_current_csect)->align < 6)
>>        symbol_get_tc (ppc_current_csect)->align = 6;
>
> Any value can be passed for the alignment of csect. Thus, it might be
> possible but I doubt it will ever happen.
> Anyway I've updated the patch.

IBM XLC aligns code CSECTs to cache line boundary (128 bytes).  I plan
to update GCC similarly, so the patch does need to ensure that it is
not reducing the alignment of the code CSECT.

Thanks, David