Hi, Thomas
> -----Original Message-----
> From: Thomas Monjalon <tho...@monjalon.net>
> Sent: Wednesday, March 20, 2024 7:37 PM
> To: fengcheng...@huawei.com; Ma, WenwuX <wenwux...@intel.com>
> Cc: dev@dpdk.org; Jiale, SongX <songx.ji...@intel.com>; sta...@dpdk.org
> Subject: Re: [PATCH v3] dmadev: fix structure alignment
>
> 20/03/2024 08:23, Wenwu Ma:
> > The structure rte_dma_dev needs to be aligned to the cache line, but
> > the return value of malloc may not be aligned to the cache line. When
> > we use memset to clear the rte_dma_dev object, it may cause a
> > segmentation fault in clang-x86-platform.
> >
> > This is because clang uses the "vmovaps" assembly instruction for
> > memset, which requires that the operands (rte_dma_dev objects) must
> > aligned on a 16-byte boundary or a general-protection exception (#GP)
> > is generated.
> >
> > Therefore, either additional memory is applied for re-alignment, or
> > the rte_dma_dev object does not require cache line alignment. The
> > patch chooses the former option to fix the issue.
> >
> > Fixes: b36970f2e13e ("dmadev: introduce DMA device library")
> > Cc: sta...@dpdk.org
> >
> > Signed-off-by: Wenwu Ma <wenwux...@intel.com>
> [..]
> > - size = dma_devices_max * sizeof(struct rte_dma_dev);
> > - rte_dma_devices = malloc(size);
> > - if (rte_dma_devices == NULL)
> > + /* The dma device object is expected to align cacheline, but
> > + * the return value of malloc may not be aligned to the cache line.
> > + * Therefore, extra memory is applied for realignment.
> > + * note: We do not call posix_memalign/aligned_alloc because it is
> > + * version dependent on libc.
> > + */
> > + size = dma_devices_max * sizeof(struct rte_dma_dev) +
> > + RTE_CACHE_LINE_SIZE;
> > + ptr = malloc(size);
> > + if (ptr == NULL)
> > return -ENOMEM;
> > - memset(rte_dma_devices, 0, size);
> > + memset(ptr, 0, size);
> > +
> > + rte_dma_devices = RTE_PTR_ALIGN(ptr, RTE_CACHE_LINE_SIZE);
>
> Why not using aligned_alloc()?
> https://en.cppreference.com/w/c/memory/aligned_alloc
>
>
because it is version dependent on libc.
