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File btf_encoder-fix-and-complete-filtering-out-zero-sized-per-CPU-variables.patch of Package dwarves (Revision dd36d006278c65200100261d5cdbe952)

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From 0d17503db0580a6635d103fed030724b38ba1364 Mon Sep 17 00:00:00 2001
From: Andrii Nakryiko <andrii@kernel.org>
Date: Mon, 24 May 2021 16:42:22 -0700
Subject: [PATCH] btf_encoder: fix and complete filtering out zero-sized
 per-CPU variables
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Upstram: accepted - expected version 1.22
Git-commit: 0d17503db0580a6635d103fed030724b38ba1364

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/

Committer notes:

Kept the {} around the if block with more than one line, which
simplifies the original patch by just removing that assignment
to the 'dwarf_name' variable.

Reported-by: Michal Suchánek <msuchanek@suse.de>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: bpf@vger.kernel.org
Cc: dwarves@vger.kernel.org
Cc: kernel-team@fb.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
 btf_encoder.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/btf_encoder.c b/btf_encoder.c
index c711f12..033c927 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
@@ -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;
 		}
@@ -600,6 +601,13 @@ 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;
 
-- 
2.31.1

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File btf_encoder-fix-and-complete-filtering-out-zero-sized-per-CPU-variables.patch of Package dwarves (Revision dd36d006278c65200100261d5cdbe952)

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