linux-kernel - [PATCH 6/9] perf symbols: Allow for .plt without header

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Message-Id: <20230127170222.9895-7-adrian.hunter@intel.com>
Date:   Fri, 27 Jan 2023 19:02:19 +0200
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Jiri Olsa <jolsa@...hat.com>, Namhyung Kim <namhyung@...nel.org>,
        Ian Rogers <irogers@...gle.com>, linux-kernel@...r.kernel.org,
        linux-perf-users@...r.kernel.org
Subject: [PATCH 6/9] perf symbols: Allow for .plt without header

A static executable can have a .plt due to the presence of IFUNCs.
In that case the .plt does not have a header. Check for whether
there is a header by comparing the number of entries to the
number of relocation entries.

Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>
---
 tools/perf/util/symbol-elf.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
index a002fc0bea03..8f7802097c72 100644
--- a/tools/perf/util/symbol-elf.c
+++ b/tools/perf/util/symbol-elf.c
@@ -489,6 +489,7 @@ int dso__synthesize_plt_symbols(struct dso *dso, struct symsrc *ss)
 	Elf *elf;
 	int nr = 0, err = -1;
 	struct rel_info ri = { .is_rela = false };
+	bool lazy_plt;
 
 	elf = ss->elf;
 	ehdr = ss->ehdr;
@@ -523,8 +524,10 @@ int dso__synthesize_plt_symbols(struct dso *dso, struct symsrc *ss)
 		plt_sym->end = plt_sym->start + shdr_plt.sh_size;
 		/* Use .plt.sec offset */
 		plt_offset = plt_sec_shdr.sh_offset;
+		lazy_plt = false;
 	} else {
-		plt_offset = shdr_plt.sh_offset + plt_header_size;
+		plt_offset = shdr_plt.sh_offset;
+		lazy_plt = true;
 	}
 
 	scn_dynsym = ss->dynsym;
@@ -577,6 +580,17 @@ int dso__synthesize_plt_symbols(struct dso *dso, struct symsrc *ss)
 
 	ri.is_rela = shdr_rel_plt.sh_type == SHT_RELA;
 
+	if (lazy_plt) {
+		/*
+		 * Assume a .plt with the same number of entries as the number
+		 * of relocation entries is not lazy and does not have a header.
+		 */
+		if (ri.nr_entries * plt_entry_size == shdr_plt.sh_size)
+			dso__delete_symbol(dso, plt_sym);
+		else
+			plt_offset += plt_header_size;
+	}
+
 	/*
 	 * x86 doesn't insert IFUNC relocations in .plt order, so sort to get
 	 * back in order.
-- 
2.34.1