linux-kernel - [PATCH] perf symbol: Fail to read phdr workaround

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Message-Id: <20220731164923.691193-1-irogers@google.com>
Date:   Sun, 31 Jul 2022 09:49:23 -0700
From:   Ian Rogers <irogers@...gle.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Leo Yan <leo.yan@...aro.org>, linux-perf-users@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     Stephane Eranian <eranian@...gle.com>,
        Ian Rogers <irogers@...gle.com>
Subject: [PATCH] perf symbol: Fail to read phdr workaround

The perf jvmti agent doesn't create program headers, in this case
fallback on section headers as happened previously.

Fixes: 882528d2e776 ("perf symbol: Skip symbols if SHF_ALLOC flag is not set")
Signed-off-by: Ian Rogers <irogers@...gle.com>
---
 tools/perf/util/symbol-elf.c | 27 ++++++++++++++++++++-------
 1 file changed, 20 insertions(+), 7 deletions(-)

diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
index b3be5b1d9dbb..75bec32d4f57 100644
--- a/tools/perf/util/symbol-elf.c
+++ b/tools/perf/util/symbol-elf.c
@@ -1305,16 +1305,29 @@ dso__load_sym_internal(struct dso *dso, struct map *map, struct symsrc *syms_ss,
 
 			if (elf_read_program_header(syms_ss->elf,
 						    (u64)sym.st_value, &phdr)) {
-				pr_warning("%s: failed to find program header for "
+				pr_debug4("%s: failed to find program header for "
 					   "symbol: %s st_value: %#" PRIx64 "\n",
 					   __func__, elf_name, (u64)sym.st_value);
-				continue;
+				pr_debug4("%s: adjusting symbol: st_value: %#" PRIx64 " "
+					"sh_addr: %#" PRIx64 " sh_offset: %#" PRIx64 "\n",
+					__func__, (u64)sym.st_value, (u64)shdr.sh_addr,
+					(u64)shdr.sh_offset);
+				/*
+				 * Fail to find program header, let's rollback
+				 * to use shdr.sh_addr and shdr.sh_offset to
+				 * calibrate symbol's file address, though this
+				 * is not necessary for normal C ELF file, we
+				 * still need to handle java JIT symbols in this
+				 * case.
+				 */
+				sym.st_value -= shdr.sh_addr - shdr.sh_offset;
+			} else {
+				pr_debug4("%s: adjusting symbol: st_value: %#" PRIx64 " "
+					"p_vaddr: %#" PRIx64 " p_offset: %#" PRIx64 "\n",
+					__func__, (u64)sym.st_value, (u64)phdr.p_vaddr,
+					(u64)phdr.p_offset);
+				sym.st_value -= phdr.p_vaddr - phdr.p_offset;
 			}
-			pr_debug4("%s: adjusting symbol: st_value: %#" PRIx64 " "
-				  "p_vaddr: %#" PRIx64 " p_offset: %#" PRIx64 "\n",
-				  __func__, (u64)sym.st_value, (u64)phdr.p_vaddr,
-				  (u64)phdr.p_offset);
-			sym.st_value -= phdr.p_vaddr - phdr.p_offset;
 		}
 
 		demangled = demangle_sym(dso, kmodule, elf_name);
-- 
2.37.1.455.g008518b4e5-goog