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[Qemu-devel] [Bug 1803872] Re: [PATCH v3 4/5] migration: Use QEMU_NONSTR
From: |
Eric Blake |
Subject: |
[Qemu-devel] [Bug 1803872] Re: [PATCH v3 4/5] migration: Use QEMU_NONSTRING for non NUL-terminated arrays |
Date: |
Tue, 18 Dec 2018 21:36:58 -0000 |
On 12/18/18 11:51 AM, Philippe Mathieu-Daudé wrote:
> GCC 8 added a -Wstringop-truncation warning:
>
> The -Wstringop-truncation warning added in GCC 8.0 via r254630 for
> bug 81117 is specifically intended to highlight likely unintended
> uses of the strncpy function that truncate the terminating NUL
> character from the source string.
>
> This new warning leads to compilation failures:
>
> CC migration/global_state.o
> qemu/migration/global_state.c: In function 'global_state_store_running':
> qemu/migration/global_state.c:45:5: error: 'strncpy' specified bound 100
> equals destination size [-Werror=stringop-truncation]
> strncpy((char *)global_state.runstate, state,
> sizeof(global_state.runstate));
>
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> make: *** [qemu/rules.mak:69: migration/global_state.o] Error 1
>
> Use the QEMU_NONSTRING attribute, since this array is intended to store
> character arrays that do not necessarily contain a terminating NUL.
> typedef struct {
> uint32_t size;
> - uint8_t runstate[100];
> + uint8_t runstate[100] QEMU_NONSTRING;
Since 100 bytes for runstate[] is larger than any string possible in our
current enum string values, could we instead add an assert that
strlen(state) < sizeof(global_state.runstate), and then use strpadcpy()
to make our intent obvious while still shutting up the compiler warning,
but without having to deal with the fallout of marking runstate as a
non-string?
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3266
Virtualization: qemu.org | libvirt.org
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https://bugs.launchpad.net/bugs/1803872
Title:
gcc 8.2 reports stringop-truncation when building qemu
Status in QEMU:
New
Bug description:
QEMU 3.0
block/sheepdog.c: In function 'find_vdi_name':
block/sheepdog.c:1239:5: error: 'strncpy' specified bound 256 equals
destination size [-Werror=stringop-truncation]
strncpy(buf + SD_MAX_VDI_LEN, tag, SD_MAX_VDI_TAG_LEN);
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
If this is the intended behavior, please suppress the warning. For
example:
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wstringop-truncation"
strncpy(buf + SD_MAX_VDI_LEN, tag, SD_MAX_VDI_TAG_LEN);
#pragma GCC diagnostic pop
This also happens on other sources, for example hw/acpi/core.c, so
another option is to suppress it globally on CFLAGS (-Wno-stringop-
truncation)
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