[compiler-rt] [lsan] Use VReport if not REGISTERS_AVAILABLE (PR #116555)

[Fangrui Song via llvm-commits]

https://github.com/MaskRay created https://github.com/llvm/llvm-project/pull/116555

Certain tests (many are from lld/test) run `... '2>&1 | count 0` to
ensure that there is no stderr message.

GetRegistersAndSP may rarely fail, leading to
a spurious failure like (with a local hack to make `count` dump the input):

```
+ /home/ray/llvm/out/asan/bin/ld.lld func1-gcs.o func2-gcs.o func3-gcs.o -o /dev/null -z gcs-report=warning -z gcs=never
+ /home/ray/llvm/out/asan/bin/count 0
Expected 0 lines, got 1.
==2403039==Unable to get registers from thread 2403018.
```

The failure can reliably be reproduced by running `ninja check-lld` a
few times under asan+lsan (see the bot
sanitizer-x86_64-linux-bootstrap-asan).
Since registers as the root set aren't very useful anyway, just switch
to VReport instead.


>From 3ac88615bf2bc2cb0ff3c694b160d9cf8a85aa35 Mon Sep 17 00:00:00 2001
From: Fangrui Song <i at maskray.me>
Date: Sun, 17 Nov 2024 11:57:01 -0800
Subject: [PATCH] =?UTF-8?q?[=F0=9D=98=80=F0=9D=97=BD=F0=9D=97=BF]=20initia?=
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Created using spr 1.3.5-bogner
---
 compiler-rt/lib/lsan/lsan_common.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/compiler-rt/lib/lsan/lsan_common.cpp b/compiler-rt/lib/lsan/lsan_common.cpp
index 5c44c000ae577b..7ab9e4ff2ac9fd 100644
--- a/compiler-rt/lib/lsan/lsan_common.cpp
+++ b/compiler-rt/lib/lsan/lsan_common.cpp
@@ -569,7 +569,7 @@ static void ProcessThreads(SuspendedThreadsList const &suspended_threads,
     PtraceRegistersStatus have_registers =
         suspended_threads.GetRegistersAndSP(i, &registers, &sp);
     if (have_registers != REGISTERS_AVAILABLE) {
-      Report("Unable to get registers from thread %llu.\n", os_id);
+      VReport(1, "Unable to get registers from thread %llu.\n", os_id);
       // If unable to get SP, consider the entire stack to be reachable unless
       // GetRegistersAndSP failed with ESRCH.
       if (have_registers == REGISTERS_UNAVAILABLE_FATAL)