On Fri, Apr 23, 2021 at 10:50 AM Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx> wrote: > > On 23/04/2021 03.15, Florent Revest wrote: > > Our formatted output helpers are currently implemented with > > snprintf-like functions which take arguments as va_list but the types > > stored in a va_list need to be known at compilation time which causes > > problems when dealing with arguments from the BPF world that are always > > u64 but considered differently depending on the format specifiers they > > are associated with at runtime. > > > > This series replaces snprintf usages with bstr_printf calls. This lets > > us construct a binary representation of arguments in bpf_printf_prepare > > at runtime that matches an ABI that is neither arch nor compiler > > specific. > > > > This solves a bug reported by Rasmus Villemoes that would mangle > > arguments on 32 bit machines. > > That's not entirely accurate. The arguments are also mangled on x86-64, > it's just that in a few cases that goes unnoticed. That's why I > suggested you try and take your test case (which I assume had been > passing with flying colours on x86-64) and rearrange the specifiers, > arguments and expected output string so that the (morally) 32 bit > arguments end up beyond those-that-end-up-in-the-reg_save_area. > > IOWs, it is the 32 bit arguments that are mangled (because they get > passed as-if they were actually 64 bits), and that applies on all > architectures; nothing to do with sizeof(long). Mh, yes, I get your point and I agree that my description does not really fit what you reported. I tried what you suggested though, with the current bpf-next/master on x86_64: BPF_SNPRINTF(out, sizeof(out), "%u %d %u %d %u %d %u %d %u %d %u %d", 1, -2, 3, -4, 5, -6, 7, -8, 9, -10, 11, -12); And out is "1 -2 3 -4 5 -6 7 -8 9 -10 11 -12" so i can't seem to be able to produce the bug you described. Do you think I'm missing something? Would you try it differently ?
