Message ID | 20200927134609.2358960-3-alistair.francis@wdc.com |
---|---|
State | New |
Headers | show |
Series | [PULL,1/2] load_elf: Remove unused address variables from callers | expand |
On Sun, 27 Sep 2020 at 15:00, Alistair Francis <alistair.francis@wdc.com> wrote: > > Reported-by: Eduardo Habkost <ehabkost@redhat.com> > Signed-off-by: Alistair Francis <alistair.francis@wdc.com> > Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org> > Message-Id: <4cf1beb7dafb9143c261d266557d3173bf160524.1598376594.git.alistair.francis@wdc.com> > --- > @@ -269,13 +258,18 @@ static RegisterInfoArray *register_init_block(DeviceState *owner, > int index = rae[i].addr / data_size; > RegisterInfo *r = &ri[index]; > > - *r = (RegisterInfo) { > - .data = data + data_size * index, > - .data_size = data_size, > - .access = &rae[i], > - .opaque = owner, > - }; > - register_init(r); > + if (data + data_size * index == 0 || !&rae[i]) { > + continue; Coverity thinks (CID 1432800) that this is dead code, because "data + data_size * index" can never be NULL[*]. What was this intending to test for ? (maybe data == NULL? Missing dereference operator ?) [*] The C spec is quite strict about what valid pointer arithmetic is; in particular adding to a NULL pointer is undefined behaviour, and pointer arithmetic that overflows and wraps around is undefined behaviour, so there's no way to get a 0 result from "ptr + offset" without the expression being UB. thanks -- PMM
On Tue, Sep 29, 2020 at 01:55:35PM +0100, Peter Maydell wrote: > On Sun, 27 Sep 2020 at 15:00, Alistair Francis <alistair.francis@wdc.com> wrote: > > > > Reported-by: Eduardo Habkost <ehabkost@redhat.com> > > Signed-off-by: Alistair Francis <alistair.francis@wdc.com> > > Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org> > > Message-Id: <4cf1beb7dafb9143c261d266557d3173bf160524.1598376594.git.alistair.francis@wdc.com> > > --- > > @@ -269,13 +258,18 @@ static RegisterInfoArray *register_init_block(DeviceState *owner, > > int index = rae[i].addr / data_size; > > RegisterInfo *r = &ri[index]; > > > > - *r = (RegisterInfo) { > > - .data = data + data_size * index, > > - .data_size = data_size, > > - .access = &rae[i], > > - .opaque = owner, > > - }; > > - register_init(r); > > + if (data + data_size * index == 0 || !&rae[i]) { > > + continue; > > Coverity thinks (CID 1432800) that this is dead code, because > "data + data_size * index" can never be NULL[*]. What was this > intending to test for ? (maybe data == NULL? Missing dereference > operator ?) I believe the original check in the old register_init() function were just to make the function more flexible by allowing NULL arguments, but it was always unnecessary. We have 4 callers of register_init_block*() and neither rae or data are NULL on those calls. > > [*] The C spec is quite strict about what valid pointer arithmetic > is; in particular adding to a NULL pointer is undefined behaviour, > and pointer arithmetic that overflows and wraps around is > undefined behaviour, so there's no way to get a 0 result from > "ptr + offset" without the expression being UB. > > thanks > -- PMM >
On Tue, Sep 29, 2020 at 6:22 AM Eduardo Habkost <ehabkost@redhat.com> wrote: > > On Tue, Sep 29, 2020 at 01:55:35PM +0100, Peter Maydell wrote: > > On Sun, 27 Sep 2020 at 15:00, Alistair Francis <alistair.francis@wdc.com> wrote: > > > > > > Reported-by: Eduardo Habkost <ehabkost@redhat.com> > > > Signed-off-by: Alistair Francis <alistair.francis@wdc.com> > > > Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org> > > > Message-Id: <4cf1beb7dafb9143c261d266557d3173bf160524.1598376594.git.alistair.francis@wdc.com> > > > --- > > > @@ -269,13 +258,18 @@ static RegisterInfoArray *register_init_block(DeviceState *owner, > > > int index = rae[i].addr / data_size; > > > RegisterInfo *r = &ri[index]; > > > > > > - *r = (RegisterInfo) { > > > - .data = data + data_size * index, > > > - .data_size = data_size, > > > - .access = &rae[i], > > > - .opaque = owner, > > > - }; > > > - register_init(r); > > > + if (data + data_size * index == 0 || !&rae[i]) { > > > + continue; > > > > Coverity thinks (CID 1432800) that this is dead code, because > > "data + data_size * index" can never be NULL[*]. What was this > > intending to test for ? (maybe data == NULL? Missing dereference > > operator ?) > > I believe the original check in the old register_init() function > were just to make the function more flexible by allowing NULL > arguments, but it was always unnecessary. We have 4 callers of > register_init_block*() and neither rae or data are NULL on those > calls. In this case *data is an array, I guess the idea was to try and catch if somehow a point in the array was NULL? I'll send a patch to remove the check. Alistair > > > > > [*] The C spec is quite strict about what valid pointer arithmetic > > is; in particular adding to a NULL pointer is undefined behaviour, > > and pointer arithmetic that overflows and wraps around is > > undefined behaviour, so there's no way to get a 0 result from > > "ptr + offset" without the expression being UB. > > > > thanks > > -- PMM > > > > -- > Eduardo >
On Thu, Oct 01, 2020 at 08:37:31AM -0700, Alistair Francis wrote: > On Tue, Sep 29, 2020 at 6:22 AM Eduardo Habkost <ehabkost@redhat.com> wrote: > > > > On Tue, Sep 29, 2020 at 01:55:35PM +0100, Peter Maydell wrote: > > > On Sun, 27 Sep 2020 at 15:00, Alistair Francis <alistair.francis@wdc.com> wrote: > > > > > > > > Reported-by: Eduardo Habkost <ehabkost@redhat.com> > > > > Signed-off-by: Alistair Francis <alistair.francis@wdc.com> > > > > Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org> > > > > Message-Id: <4cf1beb7dafb9143c261d266557d3173bf160524.1598376594.git.alistair.francis@wdc.com> > > > > --- > > > > @@ -269,13 +258,18 @@ static RegisterInfoArray *register_init_block(DeviceState *owner, > > > > int index = rae[i].addr / data_size; > > > > RegisterInfo *r = &ri[index]; > > > > > > > > - *r = (RegisterInfo) { > > > > - .data = data + data_size * index, > > > > - .data_size = data_size, > > > > - .access = &rae[i], > > > > - .opaque = owner, > > > > - }; > > > > - register_init(r); > > > > + if (data + data_size * index == 0 || !&rae[i]) { > > > > + continue; > > > > > > Coverity thinks (CID 1432800) that this is dead code, because > > > "data + data_size * index" can never be NULL[*]. What was this > > > intending to test for ? (maybe data == NULL? Missing dereference > > > operator ?) > > > > I believe the original check in the old register_init() function > > were just to make the function more flexible by allowing NULL > > arguments, but it was always unnecessary. We have 4 callers of > > register_init_block*() and neither rae or data are NULL on those > > calls. > > In this case *data is an array, I guess the idea was to try and catch > if somehow a point in the array was NULL? I don't understand what you mean. The area pointed by data doesn't contain any pointers, just the register values. > > I'll send a patch to remove the check. Thanks!
On Thu, Oct 1, 2020 at 9:05 AM Eduardo Habkost <ehabkost@redhat.com> wrote: > > On Thu, Oct 01, 2020 at 08:37:31AM -0700, Alistair Francis wrote: > > On Tue, Sep 29, 2020 at 6:22 AM Eduardo Habkost <ehabkost@redhat.com> wrote: > > > > > > On Tue, Sep 29, 2020 at 01:55:35PM +0100, Peter Maydell wrote: > > > > On Sun, 27 Sep 2020 at 15:00, Alistair Francis <alistair.francis@wdc.com> wrote: > > > > > > > > > > Reported-by: Eduardo Habkost <ehabkost@redhat.com> > > > > > Signed-off-by: Alistair Francis <alistair.francis@wdc.com> > > > > > Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org> > > > > > Message-Id: <4cf1beb7dafb9143c261d266557d3173bf160524.1598376594.git.alistair.francis@wdc.com> > > > > > --- > > > > > @@ -269,13 +258,18 @@ static RegisterInfoArray *register_init_block(DeviceState *owner, > > > > > int index = rae[i].addr / data_size; > > > > > RegisterInfo *r = &ri[index]; > > > > > > > > > > - *r = (RegisterInfo) { > > > > > - .data = data + data_size * index, > > > > > - .data_size = data_size, > > > > > - .access = &rae[i], > > > > > - .opaque = owner, > > > > > - }; > > > > > - register_init(r); > > > > > + if (data + data_size * index == 0 || !&rae[i]) { > > > > > + continue; > > > > > > > > Coverity thinks (CID 1432800) that this is dead code, because > > > > "data + data_size * index" can never be NULL[*]. What was this > > > > intending to test for ? (maybe data == NULL? Missing dereference > > > > operator ?) > > > > > > I believe the original check in the old register_init() function > > > were just to make the function more flexible by allowing NULL > > > arguments, but it was always unnecessary. We have 4 callers of > > > register_init_block*() and neither rae or data are NULL on those > > > calls. > > > > In this case *data is an array, I guess the idea was to try and catch > > if somehow a point in the array was NULL? > > I don't understand what you mean. The area pointed by data > doesn't contain any pointers, just the register values. Yeah, I don't think this was ever right. The idea I guess was to make sure that r.data was not NULL, but unless data was NULL it couldn't be. Alistair > > > > > I'll send a patch to remove the check. > > Thanks! > > -- > Eduardo >
diff --git a/hw/core/register.c b/hw/core/register.c index ddf91eb445..31038bd7cc 100644 --- a/hw/core/register.c +++ b/hw/core/register.c @@ -176,17 +176,6 @@ void register_reset(RegisterInfo *reg) } } -void register_init(RegisterInfo *reg) -{ - assert(reg); - - if (!reg->data || !reg->access) { - return; - } - - object_initialize((void *)reg, sizeof(*reg), TYPE_REGISTER); -} - void register_write_memory(void *opaque, hwaddr addr, uint64_t value, unsigned size) { @@ -269,13 +258,18 @@ static RegisterInfoArray *register_init_block(DeviceState *owner, int index = rae[i].addr / data_size; RegisterInfo *r = &ri[index]; - *r = (RegisterInfo) { - .data = data + data_size * index, - .data_size = data_size, - .access = &rae[i], - .opaque = owner, - }; - register_init(r); + if (data + data_size * index == 0 || !&rae[i]) { + continue; + } + + /* Init the register, this will zero it. */ + object_initialize((void *)r, sizeof(*r), TYPE_REGISTER); + + /* Set the properties of the register */ + r->data = data + data_size * index; + r->data_size = data_size; + r->access = &rae[i]; + r->opaque = owner; r_array->r[i] = r; } @@ -329,6 +323,7 @@ static const TypeInfo register_info = { .name = TYPE_REGISTER, .parent = TYPE_DEVICE, .class_init = register_class_init, + .instance_size = sizeof(RegisterInfo), }; static void register_register_types(void)