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Great to have such a clear criterion for > filtering. I've been finding llvm-dwarfdump invaluable for learning these things. (Aside: thanks to Omar Sandoval to introducing it to me as I've tried to wrap my head around some small parts of DWARF.) I discovered this attribute when exploring those __func__ variables: $ llvm-dwarfdump vmlinux --name=__func__ | head -n 12 vmlinux: file format elf64-x86-64 0x0001bfd3: DW_TAG_variable DW_AT_name ("__func__") DW_AT_type (0x0001c0f0 "const const char[18]") DW_AT_artificial (true) 0x0001c148: DW_TAG_variable DW_AT_name ("__func__") DW_AT_type (0x0001c552 "const const char[12]") DW_AT_artificial (true) Then it was just a quick ctrl-F through the specification to fill in the gaps. >> The "top_level" flag is intended to be a better proxy for global scoped >> variables. Currently, the DWARF loader examines the DWARF location > > Looking at this, it appears that top_level means it is a top-level > compilation unit tag, i.e. not associated with a subroutine tag (I > think?). That's kind of implicit in your explanation so I think it would > be helpful for the log to describe what it is as well as how you're > using it. Yeah, I'll spell it out more explicitly in this commit message. I do add a comment in patch 4 which explains the differences between SCOPE_GLOBAL and top_level (shown below) but something similar should be in the log message for this change too. top_level: indicates that the variable is declared at the top level of the CU, and thus it is globally scoped. artificial: indicates that the variable is a compiler-generated "fake" variable that doesn't appear in the source. scope: set by pahole to indicate the type of storage the variable has. GLOBAL indicates it is stored in static memory (as opposed to a stack variable or register) Some variables are "top_level" but not GLOBAL: e.g. current_stack_pointer, which is a register variable, despite having global CU-declarations. We don't want that, since no code could actually find this variable. Some variables are GLOBAL but not top_level: e.g. function static variables >> expression, and if the location is found to be at a constant memory >> address (not stack, register, etc), then the variable is assumed to be >> globally scoped. However, this includes a variety of variables that >> aren't truly globally scoped: most commonly, static variables in >> functions definitions. Their locations may be static, but they're not >> globally accessible in any useful way. >> >> These flags will be used by the BTF encoder to select global variables. >> >> Signed-off-by: Stephen Brennan > > > Reviewed-by: Alan Maguire Thanks! Stephen