[Devel] [PATCH RHEL10 COMMIT] selftests/breakpoints: fix compilation warnings in breakpoint_test

[Konstantin Khorenko]

The commit is pushed to "branch-rh10-6.12.0-55.52.1.5.x.vz10-ovz" and will appear at git at bitbucket.org:openvz/vzkernel.git
after rh10-6.12.0-55.52.1.5.13.vz10
------>
commit 5db635774db7ca246bed2a3443d0a2072abba6a0
Author: Konstantin Khorenko <khorenko at virtuozzo.com>
Date:   Tue Mar 24 13:14:01 2026 +0100

    selftests/breakpoints: fix compilation warnings in breakpoint_test
    
      breakpoint_test.c: In function 'read_var':
      breakpoint_test.c:186:33: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
        186 |                         sval = *(short *)&dummy_var[i];
            |                                 ^~~~~~~~~~~~~~~~~~~~~~
      breakpoint_test.c:189:33: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
        189 |                         ival = *(int *)&dummy_var[i];
            |                                 ^~~~~~~~~~~~~~~~~~~~
      breakpoint_test.c:177:52: warning: variable 'lval' set but not used [-Wunused-but-set-variable]
      breakpoint_test.c:177:36: warning: variable 'ival' set but not used [-Wunused-but-set-variable]
      breakpoint_test.c:177:26: warning: variable 'sval' set but not used [-Wunused-but-set-variable]
      breakpoint_test.c:177:14: warning: variable 'cval' set but not used [-Wunused-but-set-variable]
      breakpoint_test.c: In function 'trigger_tests':
      breakpoint_test.c:206:14: warning: unused variable 'val' [-Wunused-variable]
      breakpoint_test.c: In function 'launch_tests':
      breakpoint_test.c:335:33: warning: unused variable 'i' [-Wunused-variable]
      breakpoint_test.c: In function 'main':
      breakpoint_test.c:390:13: warning: unused variable 'ret' [-Wunused-variable]
      breakpoint_test.c: In function 'toggle_breakpoint':
      breakpoint_test.c:91:22: warning: 'xlen' may be used uninitialized [-Wmaybe-uninitialized]
         91 |         vdr7 = (xlen | xtype) << 16;
            |                ~~~~~~^~~~~~~~
    
    Fix the following warnings:
    
     - [-Wstrict-aliasing] in read_var(): suppress with a GCC diagnostic pragma --
        the type-punned reads are intentional here: we need sized memory accesses
        at specific addresses to trigger hardware breakpoints.
    
     - [-Wunused-but-set-variable] in read_var(): instead of suppressing the
        warning with a pragma, remove the unnecessary local variables (cval, sval,
        ival, lval) entirely and use volatile casts on the pointer dereferences.
        This is the correct fix because:
        1. The purpose of these reads is to trigger hardware watchpoints via
           memory access at specific addresses, not to use the values.
        2. With -O2 the compiler is free to eliminate a dead store to a
           non-volatile local, so it can remove the read altogether, which
           would silently break the test.
        3. Casting the pointer to volatile forces the compiler to emit the
           load instruction regardless of optimization level, which is
           exactly the semantics we need.
    
     - [-Wmaybe-uninitialized]: initialize xlen in toggle_breakpoint().
     - [-Wunused-variable]: remove unused variables val, i, ret.
    
    https://virtuozzo.atlassian.net/browse/VSTOR-127529
    Signed-off-by: Konstantin Khorenko <khorenko at virtuozzo.com>
    Reviewed-by: Vasileios Almpanis <vasileios.almpanis at virtuozzo.com>
    
    Feature: fix selftests
---
 .../selftests/breakpoints/breakpoint_test.c        | 24 ++++++++++++++--------
 1 file changed, 15 insertions(+), 9 deletions(-)

diff --git a/tools/testing/selftests/breakpoints/breakpoint_test.c b/tools/testing/selftests/breakpoints/breakpoint_test.c
index d46962a24724d..6a45fde12c0b5 100644
--- a/tools/testing/selftests/breakpoints/breakpoint_test.c
+++ b/tools/testing/selftests/breakpoints/breakpoint_test.c
@@ -55,7 +55,7 @@ static void toggle_breakpoint(int n, int type, int len,
 {
 	int ret;
 
-	int xtype, xlen;
+	int xtype, xlen = 0;
 	unsigned long vdr7, dr7;
 
 	switch (type) {
@@ -172,29 +172,37 @@ static void write_var(int len)
 	}
 }
 
+/*
+ * Type-punned reads are intentional here: we need sized memory accesses
+ * at specific addresses to trigger hardware breakpoints. Alternatives
+ * like memcpy() do not guarantee a single load of the required width,
+ * so we suppress the strict-aliasing warning with a pragma instead.
+ */
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wstrict-aliasing"
 static void read_var(int len)
 {
-	char cval; short sval; int ival; long long lval;
 	int i;
 
 	for (i = 0; i < 4; i++) {
 		switch (len) {
 		case 1:
-			cval = *(char *)&dummy_var[i];
+			*(volatile char *)&dummy_var[i];
 			break;
 		case 2:
-			sval = *(short *)&dummy_var[i];
+			*(volatile short *)&dummy_var[i];
 			break;
 		case 4:
-			ival = *(int *)&dummy_var[i];
+			*(volatile int *)&dummy_var[i];
 			break;
 		case 8:
-			lval = *(long long *)&dummy_var[i];
+			*(volatile long long *)&dummy_var[i];
 			break;
 		}
 		check_trapped();
 	}
 }
+#pragma GCC diagnostic pop
 
 /*
  * Do the r/w/x accesses to trigger the breakpoints. And run
@@ -203,7 +211,6 @@ static void read_var(int len)
 static void trigger_tests(void)
 {
 	int len, local, global, i;
-	char val;
 	int ret;
 
 	ret = ptrace(PTRACE_TRACEME, 0, NULL, 0);
@@ -332,7 +339,7 @@ static void launch_tests(void)
 {
 	char buf[1024];
 	unsigned int tests = 0;
-	int len, local, global, i;
+	int len, local, global;
 
 	tests += 3 * COUNT_ISN_BPS;
 	tests += sizeof(long) / 2 * 3 * COUNT_WPS;
@@ -387,7 +394,6 @@ static void launch_tests(void)
 int main(int argc, char **argv)
 {
 	pid_t pid;
-	int ret;
 
 	ksft_print_header();