Fix "flexible array member X not at end of struct" compiling with GCC-11 #348
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This was referenced Jan 24, 2023
Flamefire
reviewed
Feb 3, 2024
| } ecmd; | ||
| constexpr auto bufsize = sizeof(struct ethtool_link_settings) + sizeof(__u32)*link_mode_data_nwords; | ||
| char buf[bufsize]; | ||
| struct ethtool_link_settings& ecmd = *(struct ethtool_link_settings*)buf; |
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IMO this is technically a strict aliasing violation and hence UB. At least buf needs to be aligned as struct ethtool_link_settings and possibly a placement new needs to be used.
Idea: Using an union to enforce the size might work:
constexpr auto bufsize = sizeof(struct ethtool_link_settings) + sizeof(__u32)*link_mode_data_nwords;
union {
struct ethtool_link_settings req;
char buf[bufsize];
} ecmd;
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Fix a problem compiling with GCC-11 (present when I compiled latest Torch which includes gloo). The problem was also reported on Debian's ML, see for full context:
https://www.mail-archive.com/[email protected]/msg1875386.html
This problem should not be occurring in the first place and it's probably a bug of GCC, but luckily the workaround is quite simple too.