[dpdk-stable] [PATCH] net/ice/base: fix build error for GCC 4.8.5

[dpdk-stable] [PATCH] net/ice/base: fix build error for GCC 4.8.5

[Aman Singh]

Code changes done for build issue as reported in Bug 817
error: dereferencing type-punned pointer will break strict-aliasing rules.
added union to avoid pointer dereferencing

Fixes: 39925373a333 ("net/ice/base: add parser execution main loop")
Cc: stable@dpdk.org

Signed-off-by: Aman Singh <aman.deep.singh@intel.com>
---
 drivers/net/ice/base/ice_parser_rt.c | 36 +++++++++++++++-------------
 1 file changed, 20 insertions(+), 16 deletions(-)

diff --git a/drivers/net/ice/base/ice_parser_rt.c b/drivers/net/ice/base/ice_parser_rt.c
index 7a44675737..eb35ad0bc0 100644
--- a/drivers/net/ice/base/ice_parser_rt.c
+++ b/drivers/net/ice/base/ice_parser_rt.c
@@ -187,21 +187,23 @@ static u32 _bit_rev_u32(u32 v, int len)
 
 static u32 _hv_bit_sel(struct ice_parser_rt *rt, int start, int len)
 {
-	u64 d64, msk;
-	u8 b[8];
+	u64 msk;
+	union {
+		u64 d64;
+		u8 b[8];
+	} bit_sel;
 	int i;
 
 	int offset = GPR_HB_IDX + start / 16;
 
-	ice_memcpy(b, &rt->gpr[offset], 8, ICE_NONDMA_TO_NONDMA);
+	ice_memcpy(bit_sel.b, &rt->gpr[offset], 8, ICE_NONDMA_TO_NONDMA);
 
 	for (i = 0; i < 8; i++)
-		b[i] = _bit_rev_u8(b[i]);
+		bit_sel.b[i] = _bit_rev_u8(bit_sel.b[i]);
 
-	d64 = *(u64 *)&b[0];
 	msk = (1ul << len) - 1;
 
-	return _bit_rev_u32((u32)((d64 >> (start % 16)) & msk), len);
+	return _bit_rev_u32((u32)((bit_sel.d64 >> (start % 16)) & msk), len);
 }
 
 static u32 _pk_build(struct ice_parser_rt *rt, struct ice_np_keybuilder *kb)
@@ -444,21 +446,23 @@ static void _po_update(struct ice_parser_rt *rt, struct ice_alu *alu)
 static u16 _reg_bit_sel(struct ice_parser_rt *rt, int reg_idx,
 			int start, int len)
 {
-	u32 d32, msk;
-	u8 b[4];
-	u8 v[4];
+	u32 msk;
+	union {
+		u32 d32;
+		u8 b[4];
+	} bit_sel;
 
-	ice_memcpy(b, &rt->gpr[reg_idx + start / 16], 4, ICE_NONDMA_TO_NONDMA);
+	ice_memcpy(bit_sel.b, &rt->gpr[reg_idx + start / 16], 4,
+		   ICE_NONDMA_TO_NONDMA);
 
-	v[0] = _bit_rev_u8(b[0]);
-	v[1] = _bit_rev_u8(b[1]);
-	v[2] = _bit_rev_u8(b[2]);
-	v[3] = _bit_rev_u8(b[3]);
+	bit_sel.b[0] = _bit_rev_u8(bit_sel.b[0]);
+	bit_sel.b[1] = _bit_rev_u8(bit_sel.b[1]);
+	bit_sel.b[2] = _bit_rev_u8(bit_sel.b[2]);
+	bit_sel.b[3] = _bit_rev_u8(bit_sel.b[3]);
 
-	d32 = *(u32 *)&v[0];
 	msk = (1u << len) - 1;
 
-	return _bit_rev_u16((u16)((d32 >> (start % 16)) & msk), len);
+	return _bit_rev_u16((u16)((bit_sel.d32 >> (start % 16)) & msk), len);
 }
 
 static void _err_add(struct ice_parser_rt *rt, int idx, bool val)
-- 
2.17.1

Re: [dpdk-stable] [dpdk-dev] [PATCH] net/ice/base: fix build error for GCC 4.8.5

[David Marchand]

On Tue, Oct 5, 2021 at 2:07 PM Aman Singh <aman.deep.singh@intel.com> wrote:
>
> Code changes done for build issue as reported in Bug 817
> error: dereferencing type-punned pointer will break strict-aliasing rules.
> added union to avoid pointer dereferencing
>

About the title, Ali reproduced the issue with other versions of gcc.

This patch touches base/ code, is Intel ok with this?
Else, we could consider disabling strict aliasing for the base driver, like
$ git grep alias '**/base/meson.build'
drivers/net/fm10k/base/meson.build:    '-Wno-strict-aliasing',
'-Wno-format-extra-args',
drivers/net/i40e/base/meson.build:        '-Wno-strict-aliasing',
'-Wno-unused-but-set-variable',
drivers/net/qede/base/meson.build:        '-Wno-strict-aliasing',


Bugzilla ID: 817

> Fixes: 39925373a333 ("net/ice/base: add parser execution main loop")

No Cc: stable, this is a regression in main.

> Signed-off-by: Aman Singh <aman.deep.singh@intel.com>

Tested-by: David Marchand <david.marchand@redhat.com>


-- 
David Marchand

Re: [dpdk-stable] [dpdk-dev] [PATCH] net/ice/base: fix build error for GCC 4.8.5

[Ferruh Yigit]

On 10/5/2021 2:57 PM, David Marchand wrote:
> On Tue, Oct 5, 2021 at 2:07 PM Aman Singh <aman.deep.singh@intel.com> wrote:
>>
>> Code changes done for build issue as reported in Bug 817
>> error: dereferencing type-punned pointer will break strict-aliasing rules.
>> added union to avoid pointer dereferencing
>>
> 
> About the title, Ali reproduced the issue with other versions of gcc.
> 
> This patch touches base/ code, is Intel ok with this?
> Else, we could consider disabling strict aliasing for the base driver, like
> $ git grep alias '**/base/meson.build'
> drivers/net/fm10k/base/meson.build:    '-Wno-strict-aliasing',
> '-Wno-format-extra-args',
> drivers/net/i40e/base/meson.build:        '-Wno-strict-aliasing',
> '-Wno-unused-but-set-variable',
> drivers/net/qede/base/meson.build:        '-Wno-strict-aliasing',
> 

It has some complications to update the shared code from the DPDK, but for this
case the fix seems simple and valid, so I am for getting the fix and work on to
propagate the fix to the shared code, instead of disable the warning directly.

Mainly Qi and Beilei will be managing the shared code part, if shared code
comes with different solution, we can send an incremental patch to replace
this fix.

Briefly I am for getting the patch, hence:
Acked-by: Ferruh Yigit <ferruh.yigit@intel.com>

> 
> Bugzilla ID: 817
> 
>> Fixes: 39925373a333 ("net/ice/base: add parser execution main loop")
> 
> No Cc: stable, this is a regression in main.
> 
>> Signed-off-by: Aman Singh <aman.deep.singh@intel.com>
> 
> Tested-by: David Marchand <david.marchand@redhat.com>
> 
>