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a=lCpzRmAYbLLaTzLvsPZ7Mbvzbb8=:19 a=wKuvFiaSGQ0qltdbU6+NXLB8nM8=:19 a=Ol13hO9ccFRV9qXi2t6ftBPywas=:19 a=xqWC_Br6kY4A:10 a=Wb1JkmetP80A:10 a=GoEa3M9JfhUA:10 a=qFK5cPGej9PGuWbBexgA:9 cc=ntf awl=host:12062 X-Proofpoint-ORIG-GUID: D_w71atv-j-J0GD9YHrhYOrsGbIJGOTl X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUwNzE3MDA2NyBTYWx0ZWRfXzMGgbZtsSD6R +aIaimsQgqThN9OOpGGoqoZHDte99WXmVdeIP4P1kkKOqnJKsJr5fkINhuXYk9T9Q+FVaDAmUoH b5VRPUxQNdd8vN+2+f22C4vCSRD9+571LwJUgQUwb0Z86g9hNgYfHp7lV6LVX2WSLi9killdmzI RxYWL0l1qC+whoN2DPZVGJYTqiv2XV9cD8oWuDKnnuFLyzAQ8EZdNM1hM6NsZzoSzdx34Dtrma0 uHQFaog2bbS0ydGsBti3uQRLjTQ9BD2CUQ0BZ5KL+X36reGhJFnnCHcga46MZr6SjjgK5Gt9ZYk iLh8QCcWpHkqIvX+ybfLhchtRwYvOg/r1wNLVq3G/s97hVnr7jV6iQT/vAod20DnBGyWaegj0Wx K7J4ApeylGcf4rRzaR7u2s2nWFL4yhbsJwFVH0e7w7n2l0B4JzR7YusqhdeRsqn07ZeY8Rj1 > On Wed, 2025-07-16 at 16:15 +0100, Nick Alcock wrote: > > [...] > >> - So... a third option, which is probably the most BTFish because it's >> something BTF already does, in a sense: put everything in one section, >> call it .BTF or .BTFA or whatever, and make that section an archive of >> named BTF members, and then stuff however many BTF outputs the >> deduplication generates (or none, if we're just stuffing inputs into >> outputs without dedupping) into archive members. >> >> So, here's a possibility which seems to provide the latter option while >> still letting existing tools read the first member (likely vmlinux): >> >> The idea is that we add a *next member link field* in the BTF header, and a >> name (a strtab offset). The next member link field is an end-of-header- >> relative offset just like most of the other header fields, which chains BTF >> members together in a linked list: >> >> parent BTF >> | >> v >> children BTF -> BTF -> BTF -> ... -> BTF >> >> The parent is always first in the list. > > Hi Nick, > > You are talking about BTF section embedded in a final vmlinux binary, right? More generally, a section embedded in any object which is the result of linking two or more objects having .BTF sections: ld foo.o (.BTF) bar.o (.BTF) -> baz.o (.BTF) This covers the particular vmlinux case I think. > Could you please elaborate a bit on why do you need multiple members > within this section (in the context of your third option)? > I re-read the email but don't get it :( As I understand it: The linker deduplicates types in the set of input .BTF sections. This means that when linking foo.o and bar.o, if both compilation units refer to a type 'quux', there are two possibilities: a) The type 'quux' is the same (using C type equivalence rules) in both compilation units. Then the type is "shared" and the linker puts it only once in the first output BTF member in baz.o .BTF, the "parent". b) The type 'quux' is different in both compilation units. These are then conflicting types. Then two versions the type, foo.quux and bar.quux, are placed by the linker in the corresponding "children" member in baz.o. Graphically, the .BTF section in a linked binary would contain a one-level tree of members, with as many children as input compilation units : parent (common types) | +--- child1 (types only in child1) +--- child2 (types only in child2) . +--- childN (types only in childN) Hope this makes sense. Nick should be able to explain it better than I do.