[llvm] [symbolizer] Empty string is not an error (PR #97781)

[Serge Pavlov via llvm-commits]

https://github.com/spavloff created https://github.com/llvm/llvm-project/pull/97781

This is recommit of llvm/llvm-project#92660, reverted in llvm/llvm-project#94424.
Original commit message is below.

After commit https://github.com/llvm/llvm-project/commit/1792852f86dc75efa1f44d46b1a0daf386d64afa ([symbolizer] Change reaction on invalid input) llvm-symbolizer issues an error on malformed command instead of echoing it to the standard output, as in previous versions. It turns out this behavior broke a use case when echoing was used to check if llvm-symbolizer is working
(https://github.com/llvm/llvm-project/commit/1792852f86dc75efa1f44d46b1a0daf386d64afa#commitcomment-142161925).

With this change an empty line as input is not considered as an error anymore and does not produce any output on stderr. llvm-symbolizer still respond on empty line with line not found, this is consistent with GNU addr2line.

>From 82a6d1572ff4de1491ea58eb167967350eace9fa Mon Sep 17 00:00:00 2001
From: Serge Pavlov <sepavloff at gmail.com>
Date: Fri, 5 Jul 2024 09:10:03 +0700
Subject: [PATCH] Revert "Revert "[symbolizer] Empty string is not an error"
 (#94424)"

This reverts commit c0bb16eaf7a6c16edadfd05ba4168fa536c227e2.
---
 llvm/test/tools/llvm-symbolizer/get-input-file.test | 6 ++----
 llvm/tools/llvm-symbolizer/llvm-symbolizer.cpp      | 8 ++++++++
 2 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/llvm/test/tools/llvm-symbolizer/get-input-file.test b/llvm/test/tools/llvm-symbolizer/get-input-file.test
index 8c21816591c81a..50eb0519687186 100644
--- a/llvm/test/tools/llvm-symbolizer/get-input-file.test
+++ b/llvm/test/tools/llvm-symbolizer/get-input-file.test
@@ -1,9 +1,9 @@
 # If binary input file is not specified, llvm-symbolizer assumes it is the first
 # item in the command.
 
-# No input items at all, complain about missing input file.
+# No input items at all. Report an unknown line, but do not produce any output on stderr.
 RUN: echo | llvm-symbolizer 2>%t.1.err | FileCheck %s --check-prefix=NOSOURCE
-RUN: FileCheck --input-file=%t.1.err --check-prefix=NOFILE %s
+RUN: FileCheck --input-file=%t.1.err --implicit-check-not={{.}} --allow-empty %s
 
 # Only one input item, complain about missing addresses.
 RUN: llvm-symbolizer "foo" 2>%t.2.err | FileCheck %s --check-prefix=NOSOURCE
@@ -32,8 +32,6 @@ RUN: FileCheck --input-file=%t.7.err --check-prefix=BAD-QUOTE %s
 NOSOURCE:      ??
 NOSOURCE-NEXT: ??:0:0
 
-NOFILE: error: no input filename has been specified
-
 NOADDR: error: 'foo': no module offset has been specified
 
 NOTFOUND:  error: 'foo': [[MSG]]
diff --git a/llvm/tools/llvm-symbolizer/llvm-symbolizer.cpp b/llvm/tools/llvm-symbolizer/llvm-symbolizer.cpp
index b98bdbc388faf2..6d7953f3109a57 100644
--- a/llvm/tools/llvm-symbolizer/llvm-symbolizer.cpp
+++ b/llvm/tools/llvm-symbolizer/llvm-symbolizer.cpp
@@ -337,6 +337,14 @@ static void symbolizeInput(const opt::InputArgList &Args,
   object::BuildID BuildID(IncomingBuildID.begin(), IncomingBuildID.end());
   uint64_t Offset = 0;
   StringRef Symbol;
+
+  // An empty input string may be used to check if the process is alive and
+  // responding to input. Do not emit a message on stderr in this case but
+  // respond on stdout.
+  if (InputString.empty()) {
+    printUnknownLineInfo(ModuleName, Printer);
+    return;
+  }
   if (Error E = parseCommand(Args.getLastArgValue(OPT_obj_EQ), IsAddr2Line,
                              StringRef(InputString), Cmd, ModuleName, BuildID,
                              Symbol, Offset)) {