diff mbox series

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

Message ID 20201105221905.1350-5-dbuono@linux.vnet.ibm.com
State Accepted
Commit a58cabd0e355fc51f18db359ba260da268df26ef
Headers show
Series Add support for Control-Flow Integrity | expand

Commit Message

Daniele Buono Nov. 5, 2020, 10:19 p.m. UTC 
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(-)
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Patch

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;