[binutils-gdb] [gdb/testsuite] Fix timeout in gdb.mi/user-selected-context-sync.exp with gcc-11

[Tom de Vries]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=6179e5f1d8d54e10a128e4de9c96ecda79e788bf

commit 6179e5f1d8d54e10a128e4de9c96ecda79e788bf
Author: Tom de Vries <tdevries@suse.de>
Date:   Thu Jun 10 13:38:03 2021 +0200

    [gdb/testsuite] Fix timeout in gdb.mi/user-selected-context-sync.exp with gcc-11
    
    When running test-case gdb.mi/user-selected-context-sync.exp with gcc-11, we
    get:
    ...
    continue^M
    Continuing.^M
    FAIL: gdb.mi/user-selected-context-sync.exp: mode=all-stop: test_setup: \
      inferior 1: continue to breakpoint: continue thread 1.2 to infinite \
      loop breakpoint (timeout)
    ...
    
    This is a regression since commit aa33ea68330 "testsuite, mi: avoid a clang
    bug in 'user-selected-context-sync.exp'", which fixes a similar hang when
    using clang.
    
    The source before the commit contains:
    ...
      while (1);
    ...
    and after the commit:
    ...
      int spin = 1;
      while (spin);
    ...
    
    [ FWIW, I've filed a PR gcc/101011 - Inconsistent debug info for "while (1);"
    to mention that gcc-11 has different behaviour for these two loops. ]
    
    The problem is that:
    - the test-case expects the behaviour that a breakpoint set
      on the while line will trigger on every iteration, and
    - that is not guaranteed by either version of the loop.
    
    Fix this by using a while loop with a dummy body:
    ...
      volatile int dummy = 0;
      while (1)
        dummy = !dummy;
    ...
    and setting the breakpoint in the body.
    
    Tested on x86_64-linux with clang 10.0.1, gcc-4.8, gcc 7.5.0 and gcc 11.1.1.
    
    gdb/testsuite/ChangeLog:
    
    2021-06-10  Tom de Vries  <tdevries@suse.de>
    
            * gdb.mi/user-selected-context-sync.c (child_sub_function, main):
            Rewrite while (1) using dummy loop body.

Diff:
---
 gdb/testsuite/ChangeLog                           |  5 +++++
 gdb/testsuite/gdb.mi/user-selected-context-sync.c | 16 ++++++++--------
 2 files changed, 13 insertions(+), 8 deletions(-)

diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index 65517eacd99..37376643d32 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2021-06-10  Tom de Vries  <tdevries@suse.de>
+
+	* gdb.mi/user-selected-context-sync.c (child_sub_function, main):
+	Rewrite while (1) using dummy loop body.
+
 2021-06-10  Bhuvanendra Kumar N  <Bhuvanendra.KumarN@amd.com>
 
 	* gdb.base/foll-exec.c: convert the multi-line function call into
diff --git a/gdb/testsuite/gdb.mi/user-selected-context-sync.c b/gdb/testsuite/gdb.mi/user-selected-context-sync.c
index 9818f30277f..ebb55f87e2c 100644
--- a/gdb/testsuite/gdb.mi/user-selected-context-sync.c
+++ b/gdb/testsuite/gdb.mi/user-selected-context-sync.c
@@ -27,10 +27,10 @@ static pthread_barrier_t barrier;
 static void
 child_sub_function (void)
 {
-  /* Deliberately spin on a variable instead of plain 'while (1)' to
-     avoid the Clang bug https://bugs.llvm.org/show_bug.cgi?id=49614.  */
-  int spin = 1;
-  while (spin); /* thread loop line */
+  volatile int dummy = 0;
+  while (1)
+    /* Dummy loop body to allow setting breakpoint.  */
+    dummy = !dummy; /* thread loop line */
 }
 
 static void *
@@ -60,10 +60,10 @@ main (void)
 
   pthread_barrier_wait (&barrier);
 
-  /* Deliberately spin on a variable instead of plain 'while (1)' to
-     avoid the Clang bug https://bugs.llvm.org/show_bug.cgi?id=49614.  */
-  int spin = 1;
-  while (spin); /* main break line */
+  volatile int dummy = 0;
+  while (1)
+    /* Dummy loop body to allow setting breakpoint.  */
+    dummy = !dummy; /* main break line */
 
   return 0;
 }