Re: [PATCH dwarves] btf_encoder: fix and complete filtering out zero-sized per-CPU variables
From: Arnaldo Carvalho de Melo <acme@kernel.org>
Date: 2021-05-27 14:55:15
Em Mon, May 24, 2021 at 04:42:22PM -0700, Andrii Nakryiko escreveu:
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@mail.gmail.com/ (local)
quoted hunk ↗ jump to hunk
+++ b/btf_encoder.c@@ -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,
I just changed the above hunk to be:
@@ -583,7 +585,6 @@ int cu__encode_btf(struct cu *cu, int verbose, bool force, * per-CPU symbols have non-zero values. */ if (var->ip.addr == 0) { - dwarf_name = variable__name(var, cu); if (!dwarf_name || strcmp(dwarf_name, name)) continue; }
Which is shorter and keeps the {} around a multi line if block, ok?
Thanks, applied!
- Arnaldo