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util: Return valid allocation for qemu_try_memalign() with zero size
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> Reviewed-by: Richard Henderson <richard.henderson@linaro.org> Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
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