| Message ID | 20220304112126.2261039-5-peter.maydell@linaro.org |
|---|---|
| State | Superseded |
| Headers | show |
| Series | Cleanup of qemu_oom_check() and qemu_memalign() | expand |
On 4/3/22 12:21, Peter Maydell wrote: > Currently qemu_try_memalign()'s behaviour if asked to allocate > 0 bytes is rather variable: > * on Windows, we will assert > * on POSIX platforms, we get the underlying behaviour of > the posix_memalign() or equivalent function, which may be > either "return a valid non-NULL pointer" or "return NULL" > > Explictly check for 0 byte allocations, so we get consistent > behaviour across platforms. We handle them by incrementing the size > so that we return a valid non-NULL pointer that can later be passed > to qemu_vfree(). This is permitted behaviour for the > posix_memalign() API and is the most usual way that underlying > malloc() etc implementations handle a zero-sized allocation request, > because it won't trip up calling code that assumes NULL means an > error. (This includes our own qemu_memalign(), which will abort on > NULL.) > > This change is a preparation for sharing the qemu_try_memalign() code > between Windows and POSIX. > > Signed-off-by: Peter Maydell <peter.maydell@linaro.org> > --- > util/oslib-posix.c | 3 +++ > util/oslib-win32.c | 4 +++- > 2 files changed, 6 insertions(+), 1 deletion(-) > > diff --git a/util/oslib-posix.c b/util/oslib-posix.c > index 0278902ee79..f7e22f4ff9b 100644 > --- a/util/oslib-posix.c > +++ b/util/oslib-posix.c > @@ -209,6 +209,9 @@ void *qemu_try_memalign(size_t alignment, size_t size) > g_assert(is_power_of_2(alignment)); > } > > + if (size == 0) { > + size++; > + } > #if defined(CONFIG_POSIX_MEMALIGN) > int ret; > ret = posix_memalign(&ptr, alignment, size); > diff --git a/util/oslib-win32.c b/util/oslib-win32.c > index 05857414695..8c28d70904d 100644 > --- a/util/oslib-win32.c > +++ b/util/oslib-win32.c > @@ -48,12 +48,14 @@ void *qemu_try_memalign(size_t alignment, size_t size) > { > void *ptr; > > - g_assert(size != 0); Better, X_try_Y() functions are not supposed to fail. Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
On 3/4/22 01:21, Peter Maydell wrote: > Currently qemu_try_memalign()'s behaviour if asked to allocate > 0 bytes is rather variable: > * on Windows, we will assert > * on POSIX platforms, we get the underlying behaviour of > the posix_memalign() or equivalent function, which may be > either "return a valid non-NULL pointer" or "return NULL" > > Explictly check for 0 byte allocations, so we get consistent > behaviour across platforms. We handle them by incrementing the size > so that we return a valid non-NULL pointer that can later be passed > to qemu_vfree(). This is permitted behaviour for the > posix_memalign() API and is the most usual way that underlying > malloc() etc implementations handle a zero-sized allocation request, > because it won't trip up calling code that assumes NULL means an > error. (This includes our own qemu_memalign(), which will abort on > NULL.) > > This change is a preparation for sharing the qemu_try_memalign() code > between Windows and POSIX. > > Signed-off-by: Peter Maydell<peter.maydell@linaro.org> > --- > util/oslib-posix.c | 3 +++ > util/oslib-win32.c | 4 +++- > 2 files changed, 6 insertions(+), 1 deletion(-) Reviewed-by: Richard Henderson <richard.henderson@linaro.org> r~
diff --git a/util/oslib-posix.c b/util/oslib-posix.c index 0278902ee79..f7e22f4ff9b 100644 --- a/util/oslib-posix.c +++ b/util/oslib-posix.c @@ -209,6 +209,9 @@ void *qemu_try_memalign(size_t alignment, size_t size) g_assert(is_power_of_2(alignment)); } + if (size == 0) { + size++; + } #if defined(CONFIG_POSIX_MEMALIGN) int ret; ret = posix_memalign(&ptr, alignment, size); diff --git a/util/oslib-win32.c b/util/oslib-win32.c index 05857414695..8c28d70904d 100644 --- a/util/oslib-win32.c +++ b/util/oslib-win32.c @@ -48,12 +48,14 @@ void *qemu_try_memalign(size_t alignment, size_t size) { void *ptr; - g_assert(size != 0); if (alignment < sizeof(void *)) { alignment = sizeof(void *); } else { g_assert(is_power_of_2(alignment)); } + if (size == 0) { + size++; + } ptr = _aligned_malloc(size, alignment); trace_qemu_memalign(alignment, size, ptr); return ptr;
Currently qemu_try_memalign()'s behaviour if asked to allocate 0 bytes is rather variable: * on Windows, we will assert * on POSIX platforms, we get the underlying behaviour of the posix_memalign() or equivalent function, which may be either "return a valid non-NULL pointer" or "return NULL" Explictly check for 0 byte allocations, so we get consistent behaviour across platforms. We handle them by incrementing the size so that we return a valid non-NULL pointer that can later be passed to qemu_vfree(). This is permitted behaviour for the posix_memalign() API and is the most usual way that underlying malloc() etc implementations handle a zero-sized allocation request, because it won't trip up calling code that assumes NULL means an error. (This includes our own qemu_memalign(), which will abort on NULL.) This change is a preparation for sharing the qemu_try_memalign() code between Windows and POSIX. Signed-off-by: Peter Maydell <peter.maydell@linaro.org> --- util/oslib-posix.c | 3 +++ util/oslib-win32.c | 4 +++- 2 files changed, 6 insertions(+), 1 deletion(-)