From 41441379baa63b5471385361d08c8df317705b69 Mon Sep 17 00:00:00 2001
From: Mark Wielaard <mark@klomp.org>
Date: Sun, 30 Mar 2025 17:38:21 +0200
Subject: [PATCH] Handle top __syscall_cancel frames when getting stack traces

Since glibc 2.41 there are extra frames inserted before doing a
syscall to support proper thread cancellation.  This breaks various
suppressions and regtests involving checking syscall arguments.

Solve this by removing those extra frames from the top of the call
stack when we are processing a linux system call.

https://bugs.kde.org/show_bug.cgi?id=502126
---
 NEWS                     |  1 +
 coregrind/m_stacktrace.c | 53 +++++++++++++++++++++++++++++++++++++++-
 2 files changed, 53 insertions(+), 1 deletion(-)

diff --git a/NEWS b/NEWS
index 40b953959..7145157f2 100644
--- a/NEWS
+++ b/NEWS
@@ -70,6 +70,7 @@ are not entered into bugzilla tend to get forgotten about or ignored.
 501846  Add x86 Linux shm wrappers
 501850  FreeBSD syscall arguments 7 and 8 incorrect.
 501893  Missing suppression for __wcscat_avx2 (strcat-strlen-avx2.h.S:68)?
+502126  glibc 2.41 extra syscall_cancel frames
 
 To see details of a given bug, visit
   https://bugs.kde.org/show_bug.cgi?id=XXXXXX
diff --git a/coregrind/m_stacktrace.c b/coregrind/m_stacktrace.c
index cbeaab9db..21c0f4794 100644
--- a/coregrind/m_stacktrace.c
+++ b/coregrind/m_stacktrace.c
@@ -9,6 +9,8 @@
 
    Copyright (C) 2000-2017 Julian Seward 
       jseward@acm.org
+   Copyright (C) 2025 Mark J. Wielaard
+      mark@klomp.org
 
    This program is free software; you can redistribute it and/or
    modify it under the terms of the GNU General Public License as
@@ -1693,10 +1695,59 @@ UInt VG_(get_StackTrace_with_deltas)(
                   tid, stack_highest_byte,
                   startRegs.r_pc, startRegs.r_sp);
 
-   return VG_(get_StackTrace_wrk)(tid, ips, n_ips, 
+   Int found = VG_(get_StackTrace_wrk)(tid, ips, n_ips,
                                        sps, fps,
                                        &startRegs,
                                        stack_highest_byte);
+
+#if defined(VGO_linux)
+   /* glibc might insert some extra frames before doing a syscall to support
+      thread cancellation.  This breaks various suppressions and regtests
+      involving checking syscall arguments. So when processing a syscall just
+      remove those extra frames from the top of the call stack.  */
+   if (VG_(is_in_syscall)(tid)) {
+      Int i;
+      Int start = 0;
+      DiEpoch ep = VG_(current_DiEpoch)();
+      for (i = 0; i < found; i++) {
+         /* This could be made a little more efficient by doing the lookups
+            for the symbols at glibc load time and check the address falls
+            inside the function symbol address range here. But given this
+            is only called during syscall processing, this is probably fine
+            for now.  */
+         const HChar *buf;
+         if (VG_(get_fnname_raw)(ep, ips[i], &buf)) { // raw, don't demangle
+            if (VG_STREQ("__syscall_cancel_arch", buf) ||
+                VG_STREQ("__internal_syscall_cancel", buf) ||
+#if defined(VGP_x86_linux) || defined(VGP_arm_linux)
+                VG_STREQ("__libc_do_syscall", buf) ||
+#endif
+#if defined(VGP_x86_linux)
+                VG_STREQ("_dl_sysinfo_int80", buf) ||
+#endif
+                VG_STREQ("__syscall_cancel", buf)) {
+               start++;
+               continue; // Maybe the next one is special too?
+            } else {
+               break; // Not special, only skip top stack names.
+            }
+         } else {
+            break; // No name, not special, don't skip.
+         }
+      }
+
+      if (start > 0) {
+         for (i = 0; i < (found - start); i++) {
+            ips[i] = ips[i + start];
+            if (sps) sps[i] = sps[i + start];
+            if (fps) fps[i] = fps[i + start];
+         }
+         return found - start;
+      }
+   }
+#endif
+
+   return found;
 }
 
 UInt VG_(get_StackTrace) ( ThreadId tid, 
-- 
2.47.2