| Message ID | 20161128195701.24912-3-lersek@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Mon, Nov 28, 2016 at 11:57 AM, Laszlo Ersek <lersek@redhat.com> wrote: > According to ISO C99 / N1256 (referenced in HACKING): > >> 6.5.8 Relational operators >> >> 4 For the purposes of these operators, a pointer to an object that is >> not an element of an array behaves the same as a pointer to the first >> element of an array of length one with the type of the object as its >> element type. >> >> 5 When two pointers are compared, the result depends on the relative >> locations in the address space of the objects pointed to. If two >> pointers to object or incomplete types both point to the same object, >> or both point one past the last element of the same array object, they >> compare equal. If the objects pointed to are members of the same >> aggregate object, pointers to structure members declared later compare >> greater than pointers to members declared earlier in the structure, >> and pointers to array elements with larger subscript values compare >> greater than pointers to elements of the same array with lower >> subscript values. All pointers to members of the same union object >> compare equal. If the expression /P/ points to an element of an array >> object and the expression /Q/ points to the last element of the same >> array object, the pointer expression /Q+1/ compares greater than /P/. >> In all other cases, the behavior is undefined. > > Our AddressSpace objects are allocated generally individually, and kept in > the "address_spaces" linked list, so we mustn't compare their addresses > with relops. > > Convert the pointers subjected to the relop in rom_order_compare() to > "uintptr_t": > >> 7.18.1.4 Integer types capable of holding object pointers >> >> 1 [...] >> >> The following type designates an unsigned integer type with the >> property that any valid pointer to void can be converted to this type, >> then converted back to pointer to void, and the result will compare >> equal to the original pointer: >> >> /uintptr_t/ >> >> These types are optional. > > Cc: "Michael S. Tsirkin" <mst@redhat.com> > Cc: Alistair Francis <alistair.francis@xilinx.com> > Cc: Paolo Bonzini <pbonzini@redhat.com> > Cc: Peter Maydell <peter.maydell@linaro.org> > Cc: qemu-devel@nongnu.org > Fixes: 3e76099aacb4dae0d37ebf95305369e03d1491e6 > Signed-off-by: Laszlo Ersek <lersek@redhat.com> Reviewed-by: Alistair Francis <alistair.francis@xilinx.com> Thanks, Alistair > --- > hw/core/loader.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/hw/core/loader.c b/hw/core/loader.c > index c0d645a87134..766e48f2aec2 100644 > --- a/hw/core/loader.c > +++ b/hw/core/loader.c > @@ -818,7 +818,7 @@ static QTAILQ_HEAD(, Rom) roms = QTAILQ_HEAD_INITIALIZER(roms); > > static inline bool rom_order_compare(Rom *rom, Rom *item) > { > - return (rom->as > item->as) || > + return ((uintptr_t)(void*)rom->as > (uintptr_t)(void*)item->as) || > (rom->as == item->as && rom->addr >= item->addr); > } > > -- > 2.9.2 > >
On Mon, Nov 28, 2016 at 08:57:01PM +0100, Laszlo Ersek wrote: > According to ISO C99 / N1256 (referenced in HACKING): > > > 6.5.8 Relational operators > > > > 4 For the purposes of these operators, a pointer to an object that is > > not an element of an array behaves the same as a pointer to the first > > element of an array of length one with the type of the object as its > > element type. > > > > 5 When two pointers are compared, the result depends on the relative > > locations in the address space of the objects pointed to. If two > > pointers to object or incomplete types both point to the same object, > > or both point one past the last element of the same array object, they > > compare equal. If the objects pointed to are members of the same > > aggregate object, pointers to structure members declared later compare > > greater than pointers to members declared earlier in the structure, > > and pointers to array elements with larger subscript values compare > > greater than pointers to elements of the same array with lower > > subscript values. All pointers to members of the same union object > > compare equal. If the expression /P/ points to an element of an array > > object and the expression /Q/ points to the last element of the same > > array object, the pointer expression /Q+1/ compares greater than /P/. > > In all other cases, the behavior is undefined. > > Our AddressSpace objects are allocated generally individually, and kept in > the "address_spaces" linked list, so we mustn't compare their addresses > with relops. > > Convert the pointers subjected to the relop in rom_order_compare() to > "uintptr_t": > > > 7.18.1.4 Integer types capable of holding object pointers > > > > 1 [...] > > > > The following type designates an unsigned integer type with the > > property that any valid pointer to void can be converted to this type, > > then converted back to pointer to void, and the result will compare > > equal to the original pointer: > > > > /uintptr_t/ > > > > These types are optional. > > Cc: "Michael S. Tsirkin" <mst@redhat.com> > Cc: Alistair Francis <alistair.francis@xilinx.com> > Cc: Paolo Bonzini <pbonzini@redhat.com> > Cc: Peter Maydell <peter.maydell@linaro.org> > Cc: qemu-devel@nongnu.org > Fixes: 3e76099aacb4dae0d37ebf95305369e03d1491e6 > Signed-off-by: Laszlo Ersek <lersek@redhat.com> > --- > hw/core/loader.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/hw/core/loader.c b/hw/core/loader.c > index c0d645a87134..766e48f2aec2 100644 > --- a/hw/core/loader.c > +++ b/hw/core/loader.c > @@ -818,7 +818,7 @@ static QTAILQ_HEAD(, Rom) roms = QTAILQ_HEAD_INITIALIZER(roms); > > static inline bool rom_order_compare(Rom *rom, Rom *item) > { > - return (rom->as > item->as) || > + return ((uintptr_t)(void*)rom->as > (uintptr_t)(void*)item->as) || > (rom->as == item->as && rom->addr >= item->addr); > } Can't hurt but why cast to void *? Should not be needed. > -- > 2.9.2
On 11/29/16 17:29, Michael S. Tsirkin wrote: > On Mon, Nov 28, 2016 at 08:57:01PM +0100, Laszlo Ersek wrote: >> According to ISO C99 / N1256 (referenced in HACKING): >> >>> 6.5.8 Relational operators >>> >>> 4 For the purposes of these operators, a pointer to an object that is >>> not an element of an array behaves the same as a pointer to the first >>> element of an array of length one with the type of the object as its >>> element type. >>> >>> 5 When two pointers are compared, the result depends on the relative >>> locations in the address space of the objects pointed to. If two >>> pointers to object or incomplete types both point to the same object, >>> or both point one past the last element of the same array object, they >>> compare equal. If the objects pointed to are members of the same >>> aggregate object, pointers to structure members declared later compare >>> greater than pointers to members declared earlier in the structure, >>> and pointers to array elements with larger subscript values compare >>> greater than pointers to elements of the same array with lower >>> subscript values. All pointers to members of the same union object >>> compare equal. If the expression /P/ points to an element of an array >>> object and the expression /Q/ points to the last element of the same >>> array object, the pointer expression /Q+1/ compares greater than /P/. >>> In all other cases, the behavior is undefined. >> >> Our AddressSpace objects are allocated generally individually, and kept in >> the "address_spaces" linked list, so we mustn't compare their addresses >> with relops. >> >> Convert the pointers subjected to the relop in rom_order_compare() to >> "uintptr_t": >> >>> 7.18.1.4 Integer types capable of holding object pointers >>> >>> 1 [...] >>> >>> The following type designates an unsigned integer type with the >>> property that any valid pointer to void can be converted to this type, >>> then converted back to pointer to void, and the result will compare >>> equal to the original pointer: >>> >>> /uintptr_t/ >>> >>> These types are optional. >> >> Cc: "Michael S. Tsirkin" <mst@redhat.com> >> Cc: Alistair Francis <alistair.francis@xilinx.com> >> Cc: Paolo Bonzini <pbonzini@redhat.com> >> Cc: Peter Maydell <peter.maydell@linaro.org> >> Cc: qemu-devel@nongnu.org >> Fixes: 3e76099aacb4dae0d37ebf95305369e03d1491e6 >> Signed-off-by: Laszlo Ersek <lersek@redhat.com> >> --- >> hw/core/loader.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/hw/core/loader.c b/hw/core/loader.c >> index c0d645a87134..766e48f2aec2 100644 >> --- a/hw/core/loader.c >> +++ b/hw/core/loader.c >> @@ -818,7 +818,7 @@ static QTAILQ_HEAD(, Rom) roms = QTAILQ_HEAD_INITIALIZER(roms); >> >> static inline bool rom_order_compare(Rom *rom, Rom *item) >> { >> - return (rom->as > item->as) || >> + return ((uintptr_t)(void*)rom->as > (uintptr_t)(void*)item->as) || >> (rom->as == item->as && rom->addr >= item->addr); >> } > > Can't hurt but why cast to void *? > Should not be needed. Just to comply with the word of the standard above; it says "any valid pointer to void". > >> -- >> 2.9.2
diff --git a/hw/core/loader.c b/hw/core/loader.c index c0d645a87134..766e48f2aec2 100644 --- a/hw/core/loader.c +++ b/hw/core/loader.c @@ -818,7 +818,7 @@ static QTAILQ_HEAD(, Rom) roms = QTAILQ_HEAD_INITIALIZER(roms); static inline bool rom_order_compare(Rom *rom, Rom *item) { - return (rom->as > item->as) || + return ((uintptr_t)(void*)rom->as > (uintptr_t)(void*)item->as) || (rom->as == item->as && rom->addr >= item->addr); }