btf_encoder is ignoring zero-sized per-CPU ELF symbols, but the same has to be done for DWARF variables when matching them with ELF symbols. This is due to zero-sized DWARF variables matching unrelated (non-zero-sized) variable that happens to be allocated at the exact same address, leading to a lot of confusion in BTF. See [0] for when this causes big problems. [0] https://lore.kernel.org/bpf/CAEf4BzZ0-sihSL-UAm21JcaCCY92CqfNxycHRZYXcoj8OYb=wA@xxxxxxxxxxxxxx/ Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx> --- btf_encoder.c | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-) diff --git a/btf_encoder.c b/btf_encoder.c index c711f124b31e..672b9943a4e2 100644 --- a/btf_encoder.c +++ b/btf_encoder.c @@ -538,6 +538,7 @@ int cu__encode_btf(struct cu *cu, int verbose, bool force, cu__for_each_variable(cu, core_id, pos) { uint32_t size, type, linkage; const char *name, *dwarf_name; + const struct tag *tag; uint64_t addr; int id; @@ -550,6 +551,7 @@ int cu__encode_btf(struct cu *cu, int verbose, bool force, /* addr has to be recorded before we follow spec */ addr = var->ip.addr; + dwarf_name = variable__name(var, cu); /* DWARF takes into account .data..percpu section offset * within its segment, which for vmlinux is 0, but for kernel @@ -582,11 +584,9 @@ int cu__encode_btf(struct cu *cu, int verbose, bool force, * modules per-CPU data section has non-zero offset so all * per-CPU symbols have non-zero values. */ - if (var->ip.addr == 0) { - dwarf_name = variable__name(var, cu); + if (var->ip.addr == 0) if (!dwarf_name || strcmp(dwarf_name, name)) continue; - } if (var->spec) var = var->spec; @@ -600,6 +600,13 @@ int cu__encode_btf(struct cu *cu, int verbose, bool force, break; } + tag = cu__type(cu, var->ip.tag.type); + if (tag__size(tag, cu) == 0) { + if (btf_elf__verbose) + fprintf(stderr, "Ignoring zero-sized per-CPU variable '%s'...\n", dwarf_name ?: "<missing name>"); + continue; + } + type = var->ip.tag.type + type_id_off; linkage = var->external ? BTF_VAR_GLOBAL_ALLOCATED : BTF_VAR_STATIC; -- 2.30.2
