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From: | Luca Bonissi |
Subject: | Re: stat64 wrong on sparc64 user |
Date: | Tue, 28 Mar 2023 14:22:29 +0200 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.8.0 |
On 28/03/23 13:55, Thomas Huth wrote:
On 28/03/2023 13.48, Luca Bonissi wrote:--- qemu-20230327/linux-user/syscall_defs.h 2023-03-27 15:41:42.000000000 +0200 +++ qemu-20230327/linux-user/syscall_defs.h.new 2023-03-27 21:43:25.615115126 +0200@@ -1450,7 +1450,7 @@ struct target_stat { unsigned int st_dev; abi_ulong st_ino; unsigned int st_mode; - unsigned int st_nlink; + short int st_nlink; unsigned int st_uid;That looks wrong at a first glance. IIRC Sparc is a very strictly aligned architecture, so if the previous field "st_mode" was aligned to a 4-byte boundary, the "st_uid" field now would not be aligned anymore... are you sure about this change? Maybe it needs a padding field now?
The padding is automatic (either on Sparc or x86-64): short will be aligned to 2-byte boundary, int will be aligned to 4-byte boundary, long will be aligned to 8-byte boundary.
E.g.: st_dev=0x05060708; st_ino=0x1112131415161718; st_mode=0x1a1b1c1d; st_nlink=0x2728; st_uid=0x2a2b2c2d; st_gid=0x3a3b3c3d; st_rdev=0x35363738; st_size=0x4142434445464748; st_blksize=0x5152535455565758; will result (sparc64 - big endian): 00: 05 06 07 08 00 00 00 00 08: 11 12 13 14 15 16 17 18 10: 1A 1B 1C 1D 27 28 00 00 18: 2A 2B 2C 2D 3A 3B 3C 3D 20: 35 36 37 38 00 00 00 00 28: 41 42 43 44 45 46 47 48 30: 00 00 00 00 00 00 00 00 38: 00 00 00 00 00 00 00 00 40: 00 00 00 00 00 00 00 00 48: 51 52 53 54 55 56 57 58 50: 00 00 00 00 00 00 00 00 58: 00 00 00 00 00 00 00 00 60: 00 00 00 00 00 00 00 00 Or on x86-64 (little endian): 00: 08 07 06 05 00 00 00 00 08: 18 17 16 15 14 13 12 11 10: 1D 1C 1B 1A 28 27 00 00 18: 2D 2C 2B 2A 3D 3C 3B 3A 20: 38 37 36 35 00 00 00 00 28: 48 47 46 45 44 43 42 41 30: 00 00 00 00 00 00 00 00 38: 00 00 00 00 00 00 00 00 40: 00 00 00 00 00 00 00 00 48: 58 57 56 55 54 53 52 51 50: 00 00 00 00 00 00 00 00 58: 00 00 00 00 00 00 00 00 60: 00 00 00 00 00 00 00 00Please note the automatic padding between "st_dev" and "st_ino" (offset 0x04, 4 bytes), "st_nlink" and "st_uid" (offset 0x16, 2 bytes), "st_rdev" and "st_size" (offset 0x24, 4 bytes).
Placing st_nlink as int would result in incorrect big/little endian conversion, so it should be set as short. If you like clearer source code, you can optionally add padding, but it is not mandatory.
Thanks! Luca
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