Bug 193649
| Summary: | ring->nr_buf_size will be calculated wrongly on PPC machine | ||||||
|---|---|---|---|---|---|---|---|
| Product: | Base System | Reporter: | dongshan <thomasyang1206> | ||||
| Component: | kern | Assignee: | Vincenzo Maffione <vmaffione> | ||||
| Status: | Closed FIXED | ||||||
| Severity: | Affects Some People | CC: | delphij, thomasyang1206 | ||||
| Priority: | --- | ||||||
| Version: | 10.0-STABLE | ||||||
| Hardware: | powerpc | ||||||
| OS: | Any | ||||||
| Attachments: |
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the bug is caused as following:
imaging a 32-bit integer 0x00000800, on little endian machine, the data in
memory is arranged like this:
[0000 0000] 0000
[0000 0001] 0000
[0000 0002] 1000
[0000 0003] 0000
[0000 0004] 0000
[0000 0005] 0000
[0000 0006] 0000
[0000 0007] 0000
However, on a big endian machine, the value in memory is:
[0000 0000] 0000
[0000 0001] 0000
[0000 0002] 0000
[0000 0003] 0000
[0000 0004] 0000
[0000 0005] 1000
[0000 0006] 0000
[0000 0007] 0000
-------------------------------------------------------------------------------
Here is the trick:
uint32_t foo; // let assume the address of foo is 0x0, as showed above.
uint32_t *p = &foo;
*(uint16_t *)p = 0x00000800;
printf("foo: 0x%x", foo); // the output of foo will be 0x08000000
printf("foo1:0x%x", (uint16_t)foo); // the output will be 0x00000800
Dump the memory on big endian machine:
[0000 0000] 0000
[0000 0001] 1000
[0000 0002] 0000
[0000 0003] 0000
[0000 0004] 0000
[0000 0005] 0000
[0000 0006] 0000
[0000 0007] 0000
This seems to have been fixed in 4f80b14ce2b17100b12dc3a346fb9e6e76764e11. |
Created attachment 147337 [details] the first part log contains the bug with TX nr_buf_size = 0x8000000, the second part log is the correct one without bug When run netmap APP pkt-gen on PPC machine, say Freescale P4080, the buf size of ring ring->nr_buf_size in "netmap_mem2.c, netmap_mem_rings_create()". The declaration of nr_buf_size in struct netmap_ring is uint32_t, however it is changed to uint16_t as following: *(uint16_t *)(uintptr_t)&ring->nr_buf_size = NETMAP_BDG_BUF_SIZE(na->nm_mem); Thus buffer size will be different as the desired, and will cause Segmentation fault. after changing it as: *(uint32_t *)(uintptr_t)&ring->nr_buf_size = NETMAP_BDG_BUF_SIZE(na->nm_mem); it works well on PPC。 The log is attached, please find it, pay attention to the buf_nr_size value between the two parts log section.