From: Daniel Borkmann <dan...@iogearbox.net>
Date: Wed, 16 Aug 2017 01:45:33 +0200
> James reported that on MIPS32 bpf_trace_printk() is currently
> broken while MIPS64 works fine:
>
> bpf_trace_printk() uses conditional operators to attempt to
> pass different types to __trace_printk() depending on the
> format operators. This doesn't work as intended on 32-bit
> architectures where u32 and long are passed differently to
> u64, since the result of C conditional operators follows the
> "usual arithmetic conversions" rules, such that the values
> passed to __trace_printk() will always be u64 [causing issues
> later in the va_list handling for vscnprintf()].
>
> For example the samples/bpf/tracex5 test printed lines like
> below on MIPS32, where the fd and buf have come from the u64
> fd argument, and the size from the buf argument:
>
> [...] 1180.941542: 0x00000001: write(fd=1, buf= (null), size=6258688)
>
> Instead of this:
>
> [...] 1625.616026: 0x00000001: write(fd=1, buf=009e4000, size=512)
>
> One way to get it working is to expand various combinations
> of argument types into 8 different combinations for 32 bit
> and 64 bit kernels. Fix tested by James on MIPS32 and MIPS64
> as well that it resolves the issue.
>
> Fixes: 9c959c863f82 ("tracing: Allow BPF programs to call bpf_trace_printk()")
> Reported-by: James Hogan <james.ho...@imgtec.com>
> Tested-by: James Hogan <james.ho...@imgtec.com>
> Signed-off-by: Daniel Borkmann <dan...@iogearbox.net>
Applied and queued up for -stable, thanks Daniel.
