[PATCH] xen/grant: Mute gcc warning in steal_linear_address()

[PATCH] xen/grant: Mute gcc warning in steal_linear_address()

[Zhenzhong Duan]

Move reference of ol1e ahead or else we see below warning.

cc1: warnings being treated as errors
grant_table.c: In function 'replace_grant_pv_mapping':
grant_table.c:142: warning: 'ol1e.l1' may be used uninitialized in this function

Signed-off-by: Zhenzhong Duan <zhenzhong.duan@oracle.com>
---
 xen/arch/x86/pv/grant_table.c |    6 +++---
 1 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/xen/arch/x86/pv/grant_table.c b/xen/arch/x86/pv/grant_table.c
index 6b7d855..5180334 100644
--- a/xen/arch/x86/pv/grant_table.c
+++ b/xen/arch/x86/pv/grant_table.c
@@ -167,6 +167,9 @@ static bool steal_linear_address(unsigned long linear, l1_pgentry_t *out)
     ol1e = *pl1e;
     okay = UPDATE_ENTRY(l1, pl1e, ol1e, l1e_empty(), mfn_x(gl1mfn), curr, 0);
 
+    if ( okay )
+        *out = ol1e;
+
  out_unlock:
     page_unlock(page);
  out_put:
@@ -174,9 +177,6 @@ static bool steal_linear_address(unsigned long linear, l1_pgentry_t *out)
  out_unmap:
     unmap_domain_page(pl1e);
 
-    if ( okay )
-        *out = ol1e;
-
  out:
     return okay;
 }
-- 
1.7.3

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Re: [PATCH] xen/grant: Mute gcc warning in steal_linear_address()

[Wei Liu]

On Wed, Aug 29, 2018 at 09:06:02PM -0700, Zhenzhong Duan wrote:
> Move reference of ol1e ahead or else we see below warning.
> 
> cc1: warnings being treated as errors
> grant_table.c: In function 'replace_grant_pv_mapping':
> grant_table.c:142: warning: 'ol1e.l1' may be used uninitialized in this function
> 
> Signed-off-by: Zhenzhong Duan <zhenzhong.duan@oracle.com>

Reviewed-by: Wei Liu <wei.liu2@citrix.com>

I don't think there is a bug in the code. The compiler isn't smart
enough to figure out ol1e won't be used when okay is false.

Wei.

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Re: [PATCH] xen/grant: Mute gcc warning in steal_linear_address()

[Andrew Cooper]

On 30/08/18 05:06, Zhenzhong Duan wrote:
> Move reference of ol1e ahead or else we see below warning.
>
> cc1: warnings being treated as errors
> grant_table.c: In function 'replace_grant_pv_mapping':
> grant_table.c:142: warning: 'ol1e.l1' may be used uninitialized in this function
>
> Signed-off-by: Zhenzhong Duan <zhenzhong.duan@oracle.com>

Which version of GCC?  This is a compiler bug, and it would be useful to
highlight which version in the commit message.

The patch itself is fine.

~Andrew

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Re: [PATCH] xen/grant: Mute gcc warning in steal_linear_address()

[Jan Beulich]

>>> On 30.08.18 at 06:06, <zhenzhong.duan@oracle.com> wrote:
> Move reference of ol1e ahead or else we see below warning.
> 
> cc1: warnings being treated as errors
> grant_table.c: In function 'replace_grant_pv_mapping':
> grant_table.c:142: warning: 'ol1e.l1' may be used uninitialized in this 
> function
> 
> Signed-off-by: Zhenzhong Duan <zhenzhong.duan@oracle.com>

I'm fine with the change, but going forward please be more specific
with your descriptions: Whether or not warnings get emitted for a
certain piece of code often highly depends on compiler version. Let
us know which version you've run this into with. For the record, I'm
building on a wide range of gcc versions every once in a while, and
I've not come across this warning so far (or else I would have sent
a patch). The really old versions (4.1.x for example) can't really be
used anymore for certain other reasons anyway, and I think it's
about time we at least raise the bar a little (also for binutils, which
iirc was the actual problem with here, using a version matching in
original release time with gcc 4.1.x).

Jan



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Re: [PATCH] xen/grant: Mute gcc warning in steal_linear_address()

[Zhenzhong Duan]

在 2018/8/30 16:04, Jan Beulich 写道:
>>>> On 30.08.18 at 06:06, <zhenzhong.duan@oracle.com> wrote:
>> Move reference of ol1e ahead or else we see below warning.
>>
>> cc1: warnings being treated as errors
>> grant_table.c: In function 'replace_grant_pv_mapping':
>> grant_table.c:142: warning: 'ol1e.l1' may be used uninitialized in this
>> function
>>
>> Signed-off-by: Zhenzhong Duan <zhenzhong.duan@oracle.com>
> 
> I'm fine with the change, but going forward please be more specific
> with your descriptions: Whether or not warnings get emitted for a
> certain piece of code often highly depends on compiler version. Let
> us know which version you've run this into with. For the record, I'm
> building on a wide range of gcc versions every once in a while, and
> I've not come across this warning so far (or else I would have sent
> a patch). The really old versions (4.1.x for example) can't really be
> used anymore for certain other reasons anyway, and I think it's
> about time we at least raise the bar a little (also for binutils, which
> iirc was the actual problem with here, using a version matching in
> original release time with gcc 4.1.x).

gcc version 4.1.2 20080704 (Red Hat 4.1.2-55)

Thanks
Zhenzhong

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