David Rector via llvm-dev
2021-Jun-14 23:54 UTC
[llvm-dev] [cfe-dev] put "str" in __attribute__((annotate("str"))) to dwarf
> On Jun 14, 2021, at 5:33 PM, Y Song via cfe-dev <cfe-dev at lists.llvm.org> wrote: > > On Mon, Jun 14, 2021 at 1:25 PM David Blaikie <dblaikie at gmail.com> wrote: >> >> >> >> On Mon, Jun 14, 2021 at 12:25 PM Y Song <ys114321 at gmail.com> wrote: >>> >>> On Fri, Jun 11, 2021 at 9:59 AM Alexei Starovoitov >>> <alexei.starovoitov at gmail.com> wrote: >>>> >>>> On Fri, Jun 11, 2021 at 07:17:32AM -0400, Aaron Ballman wrote: >>>>> On Thu, Jun 10, 2021 at 8:47 PM Alexei Starovoitov >>>>> <alexei.starovoitov at gmail.com> wrote: >>>>>> >>>>>> On Thu, Jun 10, 2021 at 12:42 PM David Blaikie <dblaikie at gmail.com> wrote: >>>>>>> >>>>>>>>> >>>>>>>>> >>>>>>>>> Any suggestions/preferences for the spelling, Aaron? >>>>>>>> >>>>>>>> I don't know this domain particularly well, so takes these suggestions >>>>>>>> with a giant grain of salt: >>>>>>>> >>>>>>>> If the concept is specific to DWARF and you don't think it'll need to >>>>>>>> extend into other debug formats, you could go with `dwarf_annotate`. >>>>>>>> If it's not really a DWARF thing but is more about B[P|T]F, then >>>>>>>> `btf_annotate` or `bpf_annotate` could work, but those may be a bit >>>>>>>> mysterious to folks outside of the domain. If it's a generic debug >>>>>>>> info concept, probably `debug_info_annotate` or something. >>>>>>> >>>>>>> >>>>>>> Arguably it can/could be a generic debug info or dwarf thing, but for now we don't have any use for it other than to squirrel info along to BTF/BPF so I'm on the fence about which prefix to use exactly >>>>>>> >>>>>> >>>>>> A bit more bike shedding colors... >>>>>> >>>>>> The __rcu and __user annations might be used by the clang itself eventually. >>>>>> Currently the "sparse" tool is doing this analysis and warns users >>>>>> when __rcu pointer is incorrectly accessed in the kernel C code. >>>>>> If clang can do that directly that could be a huge selling point >>>>>> for folks to switch from gcc to clang for kernel builds. >>>>>> The front-end would treat such annotations as arbitrary string, but >>>>>> special "building-linux-kernel-pass" would interpret the semantical context. >>>>> >>>>> Are __rcu and __user annotations notionally distinct things from bpf >>>>> (and perhaps each other as well)? Distinct enough that it would make >>>>> sense to use a different attribute name for user source for each need? >>>>> I suspect the answer is yes given that the existing annotations have >>>>> their own names which are distinct, but I don't know this domain >>>>> enough to be sure. >>>> >>>> __rcu and __user don't overlap. __rcu is not a single annotation though. >>>> It's a combination of annotations in pointers, functions, macros. >>>> Some functions have: >>>> __acquires(rcu) >>>> another function might have: >>>> __acquires(rcu_bh) >>>> There are several flavors of the RCU in the kernel. >>>> So single __attribute__((rcu_annotate("foo"))) won't work even within RCU scope. >>>> But if we do: >>>> struct foo { >>>> void * __attribute__((tag("ptr.rcu_bh")) ptr; >>>> }; >>>> int bar(int) __attribute__((tag("acquires.rcu_bh")) { ... } >>>> int baz(int) __attribute__((tag("releases.rcu_bh")) { ... } >>>> int qux(int) __attribute__((tag("acquires.rcu_sched")) { ... } >>>> ... >>>> The clang pass can parse these strings and correlate one tag to another. >>>> RCU flavors come and go, so clang cannot hard code the names. >>> >>> Maybe we can name it as "bpf_tag" as it is a "tag" for "bpf" use case? >>> >>> David, in one of your early emails, you mentioned: >>> >>> ==>>> Arguably it can/could be a generic debug info or dwarf thing, but for >>> now we don't have any use for it other than to squirrel info along to >>> BTF/BPF so I'm on the fence about which prefix to use exactly >>> ==>>> >>> and suggests since it might be used in the future for non-bpf things, >>> maybe the name could be a little more generic then bpf-specific. >>> >>> Do you have any suggestions on what name to pick? >> >> >> Nah, not especially. bpf_tag sounds OK-ish to me if it suits you. >The more generic the better IMO. And, the less the need to parse string literals the better. Why not simply `__attribute__((debuginfo("arg1", "arg2", ...)))`, e.g.: ``` #define BPF_TAG(...) __attribute__((debuginfo("bpf", __VA_ARGS__))) struct foo { void * BPF_TAG("ptr","rcu","bh") ptr; }; #define BPF_RCU_TAG(PFX, ...) BPF(PFX, "rcu", __VA_ARGS__) int bar(int) BPF_RCU_TAG("acquires","bh") { ... } int baz(int) BPF_RCU_TAG("releases","bh") { ... } int qux(int) BPF_RCU_TAG("acquires","sched") { ... } ```> Sounds good. I will use "bpf_tag" as the starting point now. > Also, it is possible "bpf_tag" may appear multiple times for the same > function, declaration etc. > > For example, > #define __bpf_tag(s) __attribute__((bpf_tag(s))) > int g __bpf_tag("str1") __bpf_tag("str2"); > Let us say we introduced a LLVM vendor tag DWARF_AT_LLVM_bpf_tag. > > How do you want the above to be represented in dwarf? > > My current scheme is to put all bpf_tag's in a string, separated by ",". > This will make things simpler. So the final output will be > DWARF_AT_LLVM_bpf_tag "str1,str2" > I may need to do a discussion with the kernel folks to use a different > delimiter than ",", but we still represent all tags with ONE string. > > But alternatively, it could be represented as a list of strings like > DWARF_AT_LLVM_bpf_tag > "str1" > "str2" > is similar to DWARF_AT_location. > > The first internal representation > DWARF_AT_LLVM_bpf_tag "str1,str2" > should be easier for IR/bitcode read/write and dwarf parsing. > > What do you think? > _______________________________________________ > cfe-dev mailing list > cfe-dev at lists.llvm.org > https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev-------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20210614/a09077bf/attachment.html>
David Blaikie via llvm-dev
2021-Jun-15 01:44 UTC
[llvm-dev] [cfe-dev] put "str" in __attribute__((annotate("str"))) to dwarf
On Mon, Jun 14, 2021 at 4:54 PM David Rector <davrecthreads at gmail.com> wrote:> > > On Jun 14, 2021, at 5:33 PM, Y Song via cfe-dev <cfe-dev at lists.llvm.org> > wrote: > > On Mon, Jun 14, 2021 at 1:25 PM David Blaikie <dblaikie at gmail.com> wrote: > > > > > On Mon, Jun 14, 2021 at 12:25 PM Y Song <ys114321 at gmail.com> wrote: > > > On Fri, Jun 11, 2021 at 9:59 AM Alexei Starovoitov > <alexei.starovoitov at gmail.com> wrote: > > > On Fri, Jun 11, 2021 at 07:17:32AM -0400, Aaron Ballman wrote: > > On Thu, Jun 10, 2021 at 8:47 PM Alexei Starovoitov > <alexei.starovoitov at gmail.com> wrote: > > > On Thu, Jun 10, 2021 at 12:42 PM David Blaikie <dblaikie at gmail.com> wrote: > > > > > Any suggestions/preferences for the spelling, Aaron? > > > I don't know this domain particularly well, so takes these suggestions > with a giant grain of salt: > > If the concept is specific to DWARF and you don't think it'll need to > extend into other debug formats, you could go with `dwarf_annotate`. > If it's not really a DWARF thing but is more about B[P|T]F, then > `btf_annotate` or `bpf_annotate` could work, but those may be a bit > mysterious to folks outside of the domain. If it's a generic debug > info concept, probably `debug_info_annotate` or something. > > > > Arguably it can/could be a generic debug info or dwarf thing, but for now > we don't have any use for it other than to squirrel info along to BTF/BPF > so I'm on the fence about which prefix to use exactly > > > A bit more bike shedding colors... > > The __rcu and __user annations might be used by the clang itself > eventually. > Currently the "sparse" tool is doing this analysis and warns users > when __rcu pointer is incorrectly accessed in the kernel C code. > If clang can do that directly that could be a huge selling point > for folks to switch from gcc to clang for kernel builds. > The front-end would treat such annotations as arbitrary string, but > special "building-linux-kernel-pass" would interpret the semantical > context. > > > Are __rcu and __user annotations notionally distinct things from bpf > (and perhaps each other as well)? Distinct enough that it would make > sense to use a different attribute name for user source for each need? > I suspect the answer is yes given that the existing annotations have > their own names which are distinct, but I don't know this domain > enough to be sure. > > > __rcu and __user don't overlap. __rcu is not a single annotation though. > It's a combination of annotations in pointers, functions, macros. > Some functions have: > __acquires(rcu) > another function might have: > __acquires(rcu_bh) > There are several flavors of the RCU in the kernel. > So single __attribute__((rcu_annotate("foo"))) won't work even within RCU > scope. > But if we do: > struct foo { > void * __attribute__((tag("ptr.rcu_bh")) ptr; > }; > int bar(int) __attribute__((tag("acquires.rcu_bh")) { ... } > int baz(int) __attribute__((tag("releases.rcu_bh")) { ... } > int qux(int) __attribute__((tag("acquires.rcu_sched")) { ... } > ... > The clang pass can parse these strings and correlate one tag to another. > RCU flavors come and go, so clang cannot hard code the names. > > > Maybe we can name it as "bpf_tag" as it is a "tag" for "bpf" use case? > > David, in one of your early emails, you mentioned: > > ==> Arguably it can/could be a generic debug info or dwarf thing, but for > now we don't have any use for it other than to squirrel info along to > BTF/BPF so I'm on the fence about which prefix to use exactly > ==> > and suggests since it might be used in the future for non-bpf things, > maybe the name could be a little more generic then bpf-specific. > > Do you have any suggestions on what name to pick? > > > > Nah, not especially. bpf_tag sounds OK-ish to me if it suits you. > > > > The more generic the better IMO. And, the less the need to parse string > literals the better. > > Why not simply `__attribute__((debuginfo("arg1", "arg2", ...)))`, e.g.: > > ``` > #define BPF_TAG(...) __attribute__((debuginfo("bpf", __VA_ARGS__))) > struct foo { > void * BPF_TAG("ptr","rcu","bh") ptr; > }; > #define BPF_RCU_TAG(PFX, ...) BPF(PFX, "rcu", __VA_ARGS__) > int bar(int) BPF_RCU_TAG("acquires","bh") { ... } > int baz(int) BPF_RCU_TAG("releases","bh") { ... } > int qux(int) BPF_RCU_TAG("acquires","sched") { ... } > ``` >Unless Paul & Adrian, etc chime in in agreement of a more general name, like 'debuginfo', I'm inclined to avoid that/go with something bpf specific until there's a broader use case/proposal, something we might be able to/want to encourage GCC to support too. Otherwise we're taking a pretty broad attribute name & choosing its behavior when we don't necessarily have a lot of leverage if GCC ends up using that name for something else. & as for separate strings - maybe, but I'm not sure what that'll look like in the resulting DWARF, what sort of form would you propose using to encode that? (same question below \/)> > Sounds good. I will use "bpf_tag" as the starting point now. > Also, it is possible "bpf_tag" may appear multiple times for the same > function, declaration etc. > > For example, > #define __bpf_tag(s) __attribute__((bpf_tag(s))) > int g __bpf_tag("str1") __bpf_tag("str2"); > Let us say we introduced a LLVM vendor tag DWARF_AT_LLVM_bpf_tag. > > How do you want the above to be represented in dwarf? > > My current scheme is to put all bpf_tag's in a string, separated by ",". > This will make things simpler. So the final output will be > DWARF_AT_LLVM_bpf_tag "str1,str2" > I may need to do a discussion with the kernel folks to use a different > delimiter than ",", but we still represent all tags with ONE string. > > But alternatively, it could be represented as a list of strings like > DWARF_AT_LLVM_bpf_tag > "str1" > "str2" > is similar to DWARF_AT_location. > >What DWARF form were you thinking of using for this? There isn't a built in form that provides encoding for multiple delimited/separated strings that I know of.> > The first internal representation > DWARF_AT_LLVM_bpf_tag "str1,str2" > should be easier for IR/bitcode read/write and dwarf parsing. > > What do you think? > _______________________________________________ > cfe-dev mailing list > cfe-dev at lists.llvm.org > https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev > > >-------------- next part -------------- An HTML attachment was scrubbed... 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