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 14:58:31
Em Thu, May 27, 2021 at 11:55:10AM -0300, Arnaldo Carvalho de Melo escreveu:
Em Mon, May 24, 2021 at 04:42:22PM -0700, Andrii Nakryiko escreveu:quoted
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.quoted
See [0] for when this causes big problems.
I also added this: Reported-by: Michal Suchánek <redacted> Michal, so you tested this patch and verified it fixed the problem? If so please let me know so that I also add: Tested-by: Michal Suchánek <redacted> Thanks, - Arnaldo
quoted hunk ↗ jump to hunk
quoted
+++ 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
-- - Arnaldo