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[PATCH v3 4/9] s390x: Avoid variable size warning in ipl.h


From: Daniele Buono
Subject: [PATCH v3 4/9] s390x: Avoid variable size warning in ipl.h
Date: Thu, 5 Nov 2020 17:19:00 -0500

S390IPLState contains two IplParameterBlock, which may in turn have
either a IPLBlockPV or a IplBlockFcp, both ending with a variable
sized field (an array).

This causes a warning with clang 11 or greater, which checks that
variable sized type are only allocated at the end of the struct:

In file included from ../qemu-cfi-v3/target/s390x/diag.c:21:
../qemu-cfi-v3/hw/s390x/ipl.h:161:23: error: field 'iplb' with variable sized 
type 'IplParameterBlock' (aka 'union IplParameterBlock') not at the end of a 
struct or class is a GNU extension 
[-Werror,-Wgnu-variable-sized-type-not-at-end]
    IplParameterBlock iplb;
                      ^
../qemu-cfi-v3/hw/s390x/ipl.h:162:23: error: field 'iplb_pv' with variable 
sized type 'IplParameterBlock' (aka 'union IplParameterBlock') not at the end 
of a struct or class is a GNU extension 
[-Werror,-Wgnu-variable-sized-type-not-at-end]
    IplParameterBlock iplb_pv;

In this case, however, the warning is a false positive, because
IPLBlockPV and IplBlockFcp are allocated in a union wrapped at 4K,
making the union non-variable sized.

Fix the warning by turning the two variable sized arrays into arrays
of size 0. This avoids the compiler error and should produce the
same code.

Signed-off-by: Daniele Buono <dbuono@linux.vnet.ibm.com>
---
There is the possibility of removing  IplBlockFcp from
IplParameterBlock, since it is not actually used.
This would also allow to entirely remove the definition of
IplBlockFcp, but we may want to keep it for completeness.

 hw/s390x/ipl.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/hw/s390x/ipl.h b/hw/s390x/ipl.h
index 9e90169695..dfc6dfd89c 100644
--- a/hw/s390x/ipl.h
+++ b/hw/s390x/ipl.h
@@ -32,7 +32,7 @@ struct IPLBlockPV {
     uint32_t num_comp;          /* 0x74 */
     uint64_t pv_header_addr;    /* 0x78 */
     uint64_t pv_header_len;     /* 0x80 */
-    struct IPLBlockPVComp components[];
+    struct IPLBlockPVComp components[0];
 } QEMU_PACKED;
 typedef struct IPLBlockPV IPLBlockPV;
 
@@ -63,7 +63,7 @@ struct IplBlockFcp {
     uint64_t br_lba;
     uint32_t scp_data_len;
     uint8_t  reserved6[260];
-    uint8_t  scp_data[];
+    uint8_t  scp_data[0];
 } QEMU_PACKED;
 typedef struct IplBlockFcp IplBlockFcp;
 
-- 
2.17.1




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