| Message ID | 20191004025509.3012-1-david@gibson.dropbear.id.au (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | exynos4210_gic: Suppress gcc9 format-truncation warnings | expand |
On 10/4/19 4:55 AM, David Gibson wrote: > exynos4210_gic_realize() prints the number of cpus into some temporary > buffers, but it only allows 3 bytes space for it. That's plenty - I'm > pretty sure that existing machines will only ever set this value to 2 > (EXYNOS4210_NCPUS). But the compiler can't really be expected to figure > that out. > > Some[*] gcc9 versions therefore emit -Wformat-truncation warnings. Fix > that by allowing more space in the temporary buffers - these are on stack > very briefly before being essentially strdup()ed inside the memory region > code, so there's not much cost to doing so. > > [*] The bizarre thing here, is that I've long gotten these warnings > compiling in a 32-bit x86 container as host - Fedora 30 with > gcc-9.2.1-1.fc30.i686 - but it compiles just fine on my normal x86_64 host > - Fedora 30 with and gcc-9.2.1-1.fc30.x86_64. > > Signed-off-by: David Gibson <david@gibson.dropbear.id.au> > --- > hw/intc/exynos4210_gic.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/hw/intc/exynos4210_gic.c b/hw/intc/exynos4210_gic.c > index a1b699b6ba..2e5e47f9ec 100644 > --- a/hw/intc/exynos4210_gic.c > +++ b/hw/intc/exynos4210_gic.c > @@ -290,8 +290,8 @@ static void exynos4210_gic_realize(DeviceState *dev, Error **errp) > SysBusDevice *sbd = SYS_BUS_DEVICE(obj); > const char cpu_prefix[] = "exynos4210-gic-alias_cpu"; > const char dist_prefix[] = "exynos4210-gic-alias_dist"; > - char cpu_alias_name[sizeof(cpu_prefix) + 3]; > - char dist_alias_name[sizeof(cpu_prefix) + 3]; > + char cpu_alias_name[sizeof(cpu_prefix) + 10]; > + char dist_alias_name[sizeof(cpu_prefix) + 10]; Hmm magic again... So GCC provides a new warning with no helpful definitions about how to clean this :( We already have: #define UUID_FMT_LEN 36 What about adding/using UINT32_FMT_LEN? > SysBusDevice *gicbusdev; > uint32_t i; > >
On Fri, 4 Oct 2019 at 04:10, David Gibson <david@gibson.dropbear.id.au> wrote: > > exynos4210_gic_realize() prints the number of cpus into some temporary > buffers, but it only allows 3 bytes space for it. That's plenty - I'm > pretty sure that existing machines will only ever set this value to 2 > (EXYNOS4210_NCPUS). But the compiler can't really be expected to figure > that out. > > Some[*] gcc9 versions therefore emit -Wformat-truncation warnings. Fix > that by allowing more space in the temporary buffers - these are on stack > very briefly before being essentially strdup()ed inside the memory region > code, so there's not much cost to doing so. > > [*] The bizarre thing here, is that I've long gotten these warnings > compiling in a 32-bit x86 container as host - Fedora 30 with > gcc-9.2.1-1.fc30.i686 - but it compiles just fine on my normal x86_64 host > - Fedora 30 with and gcc-9.2.1-1.fc30.x86_64. > > Signed-off-by: David Gibson <david@gibson.dropbear.id.au> > --- > hw/intc/exynos4210_gic.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/hw/intc/exynos4210_gic.c b/hw/intc/exynos4210_gic.c > index a1b699b6ba..2e5e47f9ec 100644 > --- a/hw/intc/exynos4210_gic.c > +++ b/hw/intc/exynos4210_gic.c > @@ -290,8 +290,8 @@ static void exynos4210_gic_realize(DeviceState *dev, Error **errp) > SysBusDevice *sbd = SYS_BUS_DEVICE(obj); > const char cpu_prefix[] = "exynos4210-gic-alias_cpu"; > const char dist_prefix[] = "exynos4210-gic-alias_dist"; > - char cpu_alias_name[sizeof(cpu_prefix) + 3]; > - char dist_alias_name[sizeof(cpu_prefix) + 3]; > + char cpu_alias_name[sizeof(cpu_prefix) + 10]; > + char dist_alias_name[sizeof(cpu_prefix) + 10]; > SysBusDevice *gicbusdev; > uint32_t i; If we assert() that num_cpu is always <= EXYNOS4210_NCPUS is that sufficient to clue gcc in that the buffer can't overflow? thanks -- PMM
On Mon, Oct 14, 2019 at 01:51:39PM +0100, Peter Maydell wrote: > On Fri, 4 Oct 2019 at 04:10, David Gibson <david@gibson.dropbear.id.au> wrote: > > > > exynos4210_gic_realize() prints the number of cpus into some temporary > > buffers, but it only allows 3 bytes space for it. That's plenty - I'm > > pretty sure that existing machines will only ever set this value to 2 > > (EXYNOS4210_NCPUS). But the compiler can't really be expected to figure > > that out. > > > > Some[*] gcc9 versions therefore emit -Wformat-truncation warnings. Fix > > that by allowing more space in the temporary buffers - these are on stack > > very briefly before being essentially strdup()ed inside the memory region > > code, so there's not much cost to doing so. > > > > [*] The bizarre thing here, is that I've long gotten these warnings > > compiling in a 32-bit x86 container as host - Fedora 30 with > > gcc-9.2.1-1.fc30.i686 - but it compiles just fine on my normal x86_64 host > > - Fedora 30 with and gcc-9.2.1-1.fc30.x86_64. > > > > Signed-off-by: David Gibson <david@gibson.dropbear.id.au> > > --- > > hw/intc/exynos4210_gic.c | 4 ++-- > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > > diff --git a/hw/intc/exynos4210_gic.c b/hw/intc/exynos4210_gic.c > > index a1b699b6ba..2e5e47f9ec 100644 > > --- a/hw/intc/exynos4210_gic.c > > +++ b/hw/intc/exynos4210_gic.c > > @@ -290,8 +290,8 @@ static void exynos4210_gic_realize(DeviceState *dev, Error **errp) > > SysBusDevice *sbd = SYS_BUS_DEVICE(obj); > > const char cpu_prefix[] = "exynos4210-gic-alias_cpu"; > > const char dist_prefix[] = "exynos4210-gic-alias_dist"; > > - char cpu_alias_name[sizeof(cpu_prefix) + 3]; > > - char dist_alias_name[sizeof(cpu_prefix) + 3]; > > + char cpu_alias_name[sizeof(cpu_prefix) + 10]; > > + char dist_alias_name[sizeof(cpu_prefix) + 10]; > > SysBusDevice *gicbusdev; > > uint32_t i; > > If we assert() that num_cpu is always <= EXYNOS4210_NCPUS > is that sufficient to clue gcc in that the buffer can't overflow? Interestingly, assert(s->num_cpu <= EXYNOS$210_NCPUS) is *not* sufficient, but assert(i <= EXYNOS4210_NCPUS) within the loop *is* enough. I've updated my patch accordingly. This isn't 4.2 material, obviously. Should I just sit on it until 5.0 opens, or does one of you have someplace to stage the patch in the meanwhile?
On Wed, 20 Nov 2019 at 05:27, David Gibson <david@gibson.dropbear.id.au> wrote: > > On Mon, Oct 14, 2019 at 01:51:39PM +0100, Peter Maydell wrote: > > If we assert() that num_cpu is always <= EXYNOS4210_NCPUS > > is that sufficient to clue gcc in that the buffer can't overflow? > > Interestingly, assert(s->num_cpu <= EXYNOS$210_NCPUS) is *not* > sufficient, but assert(i <= EXYNOS4210_NCPUS) within the loop *is* > enough. I've updated my patch accordingly. > > This isn't 4.2 material, obviously. Should I just sit on it until 5.0 > opens, or does one of you have someplace to stage the patch in the > meanwhile? Easy fixes for compiler warnings aren't inherently out of scope for 4.2. I'm also collecting stuff for 5.0 anyway so I suggest you just send the patch. -- PMM
On Wed, Nov 20, 2019 at 10:31:48AM +0000, Peter Maydell wrote: > On Wed, 20 Nov 2019 at 05:27, David Gibson <david@gibson.dropbear.id.au> wrote: > > > > On Mon, Oct 14, 2019 at 01:51:39PM +0100, Peter Maydell wrote: > > > If we assert() that num_cpu is always <= EXYNOS4210_NCPUS > > > is that sufficient to clue gcc in that the buffer can't overflow? > > > > Interestingly, assert(s->num_cpu <= EXYNOS$210_NCPUS) is *not* > > sufficient, but assert(i <= EXYNOS4210_NCPUS) within the loop *is* > > enough. I've updated my patch accordingly. > > > > This isn't 4.2 material, obviously. Should I just sit on it until 5.0 > > opens, or does one of you have someplace to stage the patch in the > > meanwhile? > > Easy fixes for compiler warnings aren't inherently out of scope > for 4.2. I'm also collecting stuff for 5.0 anyway so I suggest you > just send the patch. Ok, done.
diff --git a/hw/intc/exynos4210_gic.c b/hw/intc/exynos4210_gic.c index a1b699b6ba..2e5e47f9ec 100644 --- a/hw/intc/exynos4210_gic.c +++ b/hw/intc/exynos4210_gic.c @@ -290,8 +290,8 @@ static void exynos4210_gic_realize(DeviceState *dev, Error **errp) SysBusDevice *sbd = SYS_BUS_DEVICE(obj); const char cpu_prefix[] = "exynos4210-gic-alias_cpu"; const char dist_prefix[] = "exynos4210-gic-alias_dist"; - char cpu_alias_name[sizeof(cpu_prefix) + 3]; - char dist_alias_name[sizeof(cpu_prefix) + 3]; + char cpu_alias_name[sizeof(cpu_prefix) + 10]; + char dist_alias_name[sizeof(cpu_prefix) + 10]; SysBusDevice *gicbusdev; uint32_t i;
exynos4210_gic_realize() prints the number of cpus into some temporary buffers, but it only allows 3 bytes space for it. That's plenty - I'm pretty sure that existing machines will only ever set this value to 2 (EXYNOS4210_NCPUS). But the compiler can't really be expected to figure that out. Some[*] gcc9 versions therefore emit -Wformat-truncation warnings. Fix that by allowing more space in the temporary buffers - these are on stack very briefly before being essentially strdup()ed inside the memory region code, so there's not much cost to doing so. [*] The bizarre thing here, is that I've long gotten these warnings compiling in a 32-bit x86 container as host - Fedora 30 with gcc-9.2.1-1.fc30.i686 - but it compiles just fine on my normal x86_64 host - Fedora 30 with and gcc-9.2.1-1.fc30.x86_64. Signed-off-by: David Gibson <david@gibson.dropbear.id.au> --- hw/intc/exynos4210_gic.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)