gccgo, syscall: unknowndefine TUNSETIFF IOCTL const and others

[laboger]

This problem was reported in gccgo from gcc 5 (latest branch) when built on ppc64le because the IOCTL constant value TUNSETIFF is not defined in gccgo, but is available in gc from golang 1.5 in the generated files zerrors_linux_ppc64.go and zerrors_linu_ppc64le.go.

In the gccgo build, I can see that HAVE_LINUX_IF_TUN_H is defined, which allows the correct include file for these defines to be found, but mksysinfo.sh does not appear to handle them correctly. Instead the gen-sysinfo.go file contains:

// unknowndefine TUNSETIFF _IOW('T', 202, int)

for this define and all the other TUNSET* constants.

Possibly because it is a macro defined in terms of another macro and mksysinfo.sh doesn't handle that case?

This same problem occurred months ago with other IOCTL constants TIOCS* and the fix was to add some lines to mksysinfo.sh to enable them to be generated. I don't know if this is the same kind of problem and could be solved the same way.

The request would be to add all the TUNSET* constants to gccgo in the gcc5 branch if possible.

[laboger]

My earlier comment about the define of HAVE_LINUX_IF_TUN_H was referring to powerpc64le-linux/libgo/config.h which is generated during the gccgo build.

[ianlancetaylor]

mksysinfo.sh can handle macros defined in terms of macros. What it can't handle are macros that are defined as expressions more complex than the code in gcc/godump.c can parse. At least on my system the issue is that the TUNSET macros are defined using sizeof. Something like the earlier TIOCS* fix is what is required here.

[gopherbot]

CL https://golang.org/cl/12491 mentions this issue.