* [Xen-devel] RFC disable GCC 9 -Waddress-of-packed-member
@ 2019-11-27 22:44 Stefano Stabellini
2019-11-27 22:48 ` Andrew Cooper
0 siblings, 1 reply; 3+ messages in thread
From: Stefano Stabellini @ 2019-11-27 22:44 UTC (permalink / raw)
To: xen-devel
Cc: sstabellini, julien, wl, konrad.wilk, George.Dunlap,
andrew.cooper3, ian.jackson, jbeulich
Hi all,
GCC 9 introduced a new warning: address-of-packed-member. It warns when
a pointer points to a member of a packed struct, leading to a build
failure in Xen (cross compiling Xen on Arm with GCC 9.2):
556 trace.c: In function '__trace_hypercall':
557 trace.c:826:19: error: taking address of packed member of 'struct <anonymous>' may result in an unaligned pointer value
[-Werror=address-of-packed-member]
558 826 | uint32_t *a = d.args;
Looking at the code, I cannot see anything wrong with what we are doing.
At least on Arm, it looks OK? Anything I am missing?
If you can spot anything wrong with the Xen code, do let me know.
Otherwise, I am thinking of disabling the warning:
diff --git a/xen/Rules.mk b/xen/Rules.mk
index 5337e20..8d5c77c 100644
--- a/xen/Rules.mk
+++ b/xen/Rules.mk
@@ -86,6 +86,9 @@ CFLAGS += $(CFLAGS-y)
# allow extra CFLAGS externally via EXTRA_CFLAGS_XEN_CORE
CFLAGS += $(EXTRA_CFLAGS_XEN_CORE)
+# Disable GCC 9 warning about pointers to members of a packed struct
+CFLAGS += -Wno-address-of-packed-member
+
# Most CFLAGS are safe for assembly files:
# -std=gnu{89,99} gets confused by #-prefixed end-of-line comments
# -flto makes no sense and annoys clang
Cheers,
Stefano
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^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [Xen-devel] RFC disable GCC 9 -Waddress-of-packed-member
2019-11-27 22:44 [Xen-devel] RFC disable GCC 9 -Waddress-of-packed-member Stefano Stabellini
@ 2019-11-27 22:48 ` Andrew Cooper
2019-11-27 22:50 ` Stefano Stabellini
0 siblings, 1 reply; 3+ messages in thread
From: Andrew Cooper @ 2019-11-27 22:48 UTC (permalink / raw)
To: Stefano Stabellini, xen-devel
Cc: julien, wl, konrad.wilk, George.Dunlap, ian.jackson, jbeulich
On 27/11/2019 22:44, Stefano Stabellini wrote:
> Hi all,
>
> GCC 9 introduced a new warning: address-of-packed-member. It warns when
> a pointer points to a member of a packed struct, leading to a build
> failure in Xen (cross compiling Xen on Arm with GCC 9.2):
>
> 556 trace.c: In function '__trace_hypercall':
> 557 trace.c:826:19: error: taking address of packed member of 'struct <anonymous>' may result in an unaligned pointer value
> [-Werror=address-of-packed-member]
> 558 826 | uint32_t *a = d.args;
>
> Looking at the code, I cannot see anything wrong with what we are doing.
> At least on Arm, it looks OK? Anything I am missing?
c/s 3fd3b266d4 at a guess.
~Andrew
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^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [Xen-devel] RFC disable GCC 9 -Waddress-of-packed-member
2019-11-27 22:48 ` Andrew Cooper
@ 2019-11-27 22:50 ` Stefano Stabellini
0 siblings, 0 replies; 3+ messages in thread
From: Stefano Stabellini @ 2019-11-27 22:50 UTC (permalink / raw)
To: Andrew Cooper
Cc: Stefano Stabellini, julien, wl, konrad.wilk, George.Dunlap,
ian.jackson, jbeulich, xen-devel
On Wed, 27 Nov 2019, Andrew Cooper wrote:
> On 27/11/2019 22:44, Stefano Stabellini wrote:
> > Hi all,
> >
> > GCC 9 introduced a new warning: address-of-packed-member. It warns when
> > a pointer points to a member of a packed struct, leading to a build
> > failure in Xen (cross compiling Xen on Arm with GCC 9.2):
> >
> > 556 trace.c: In function '__trace_hypercall':
> > 557 trace.c:826:19: error: taking address of packed member of 'struct <anonymous>' may result in an unaligned pointer value
> > [-Werror=address-of-packed-member]
> > 558 826 | uint32_t *a = d.args;
> >
> > Looking at the code, I cannot see anything wrong with what we are doing.
> > At least on Arm, it looks OK? Anything I am missing?
>
> c/s 3fd3b266d4 at a guess.
Thank you! I missed it :-/
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^ permalink raw reply [flat|nested] 3+ messages in thread
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2019-11-27 22:44 [Xen-devel] RFC disable GCC 9 -Waddress-of-packed-member Stefano Stabellini
2019-11-27 22:48 ` Andrew Cooper
2019-11-27 22:50 ` Stefano Stabellini
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