Messages in this thread | | | Date | Fri, 29 May 2015 18:27:52 -0700 | From | Alexei Starovoitov <> | Subject | Re: [RFC PATCH v2 09/15] perf probe: Support $params without debuginfo |
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On 5/29/15 4:55 PM, Masami Hiramatsu wrote: > On 2015/05/29 15:30, He Kuang wrote: >> hi, Alexei >> >> On 2015/5/29 2:10, Alexei Starovoitov wrote: >>> On 5/28/15 6:01 AM, He Kuang wrote: >>>>> I don't think you can break it down in two steps like this. >>>>>> There is no such thing as 'calling regs'. x86_32 with ax,dx,cx >>>>>> are not 'calling regs'. 64-bit values will be passed in a pair. >>>>>> Only 'pt_regs + arch + func_proto + asmlinkage' makes sense >>>>> >from the user point of view. >>>>>> Adding 'asmlinkage' attr is also trivial. >>>>>> 'func(long, char) asmlinkage' is easy to parse and the user >>>> I think at this early stage, we could make our bpf variable >>>> prologue work with debuginfo while keeping bpf 'SEC' syntax >>>> consistent with original perf probe. After all, we can use >>>> pt_regs directly or relay to perf-probe cache by Masami to deal >>>> with non-debug cases. >>> >>> so you're saying you don't want to support non-debug case for now? >>> Sure, as long as section name parser will be able to support >>> 'func(long, char) asmlinkage' syntax in the future without breaking >>> compatibility. I'm mostly interested in cases when debug info >>> is not available at all. So perf-probe cache is of no use to me. >>> >>> >> >> Yes, that syntax do deal with the situation which current 'perf >> probe' syntax not covered, so not only bpf prologue would benifit >> from that, maybe we could try to let perf probe involve that. > > Hmm, then how about below syntax? > > perf probe x86_acpi_enter_sleep_state $regparams:asmlinkage(char) > > So, regparams has following synopsis. > > $regparams[:[asmlinkage|0-6]([u8|u16|u32|u64|ptr][,...])]
the number doesn't make sense in generic command. Only x86_32 plays with calling convention. All other archs are not doing anything special for asmlinkage. I think the following is enough: $regparams[[:asmlinkage]([u8|u16|u32|u64|ptr|char|short|long| long long|void*][,...])] asmlinkage most of the time won't be used and typical command will look like: 'func=func $regparams(char, long, void*)' which is ok for kprobe. For bpf section name I would still prefer 'func(char, long, void*)' since it's more concise, easier to remember, more similar to C declaration.
> Note that asmlinkage is a synonym of 0, and default depends on arch :) > Some architecture ignores this part, e.g. x86_64 always uses regs. > And it is automatically expanded to argX="%reg or $stackX". > > e.g. > $regparams is expanded to > arg1=%di arg2=%si arg3=%dx arg4=%cx arg5=%r8 arg6=%r9 (on x86_64) > arg1=%ax arg2=%dx arg3=%cx arg4=$stack1 arg5=$stack2 arg6=$stack3 (on i386) > > $regparams:0 is expanded to > arg1=%di arg2=%si arg3=%dx arg4=%cx arg5=%r8 arg6=%r9 (on x86_64) > arg1=$stack1 arg2=$stack2 arg3=$stack3 arg4=$stack4 arg5=$stack5 arg6=$stack6 (on i386) > > $regparams:3(char,long) is expanded to > arg1=%di:s8 arg2=%si:s64 (on x86_64) > arg1=%ax:s8 arg2=%dx:s64 (on i386) > > How is this? > > Thank you, > >
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