hi, Alexei On 2015/5/27 1:50, Alexei Starovoitov wrote: > On 5/25/15 1:33 AM, He Kuang wrote: >> Right, I learnt regparm(3) is mandatory in x86_32, according to rules, >> the first three args will go to regparm(ax, dx, cx). But we should not >> refer arg1~3 to ax, dx, cx because of 64bit parameters (other reasons?). >> >> Consider this keyword is used for generating bpf prologue which fetches >> formal parameters when no debuginfo is provided, for this purpose, we can: >> 1) We just help fetch the $regs or $regparms(If the keyword is >> $regparms, ax/dx/cx is fetched, nothing related to args) to bpf arglists >> and leave the rest things to bpf prog writer. >> >> 2) Keep that on platforms like x86_64 and skip this feature on >> platforms like x86_32. >> >> or any other suggestions? > > Single argument like $regparam or whatever name cannot work on all > architectures, that's why in the very beginning I suggested > 'func(long, char, void*)' syntax to describe arguments when debuginfo > is not available. Calling convention for scalars is simple enough on > all major architectures. x64_64 - trivial, i64_32 - a bit more involved, > but simple enough so that list of types of arguments is enough to figure > out which register or register pair or stack should be used to fetch > argN. > > As Masami has reminded, the use of 'asmlinkage' forces regparm=0, and we can't destinguish them without debuginfo, so 'func(long, char, void*)' syntax not work in everywhere.
In fact, all the context infos are there in bpf prog(pt_regs in arg1). To the non-debuginfo case, without the help of prologue, user steps following flow to fetch params: 1. pt_regs(arg1) + architecture => calling regs 2. calling regs + function prototype(SEC) + gcc attributes(like asmlinkage) => formal parameters '$regparms' do the 1st step, though not a full workaround. But for the lack of gcc attributes, it seems we can't do the 2nd step. Any ideas? Thanks -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
