On 14/07/2026 22:03, Torbjörn SVENSSON wrote:
Is there any better way to test if the target will trap or not on the deref?
Ok for trunk, releases/gcc-16 and releases/gcc-15?
Kind regards,
Torbjörn
--
As arm-none-eabi targets might have readable memory at address 0,
g++.dg/torture/pr101373.C test will "work" on some targets, while others
might tigger a fault. To avoid the ambiguity, lest skip the test if
target allows null to be dereferenced.
PR testsuite/126261
gcc/ChangeLog:
* doc/sourcebuild.texi (can_deref_null): Document.
gcc/testsuite/ChangeLog:
* g++.dg/torture/pr101373.C: Use effective-target can_deref_null.
* lib/target-supports.exp (check_effective_target_can_deref_null):
New proc.
Signed-off-by: Torbjörn SVENSSON <[email protected]>
---
gcc/doc/sourcebuild.texi | 4 ++++
gcc/testsuite/g++.dg/torture/pr101373.C | 1 +
gcc/testsuite/lib/target-supports.exp | 22 ++++++++++++++++++++++
3 files changed, 27 insertions(+)
diff --git a/gcc/doc/sourcebuild.texi b/gcc/doc/sourcebuild.texi
index 0e08ef5e645..e2530cf159d 100644
--- a/gcc/doc/sourcebuild.texi
+++ b/gcc/doc/sourcebuild.texi
@@ -2739,6 +2739,10 @@ Target supports the execution of @code{amx-movrs}
instructions.
@item amx_fp8
Target supports the execution of @code{amx-fp8} instructions.
+@item can_deref_null
+Target runtime permits dereferencing a null pointer without trapping, for
+example because address zero is mapped and readable.
+
@item cell_hw
Test system can execute AltiVec and Cell PPU instructions.
diff --git a/gcc/testsuite/g++.dg/torture/pr101373.C b/gcc/testsuite/g++.dg/torture/pr101373.C
index f8c809739e2..45f1e455eec 100644
--- a/gcc/testsuite/g++.dg/torture/pr101373.C
+++ b/gcc/testsuite/g++.dg/torture/pr101373.C
@@ -1,5 +1,6 @@
// { dg-do run }
// { dg-xfail-run-if "PR100409" { *-*-* } }
+// { dg-skip-if "PR126261" { can_deref_null } }
int __attribute__((const,noipa)) foo (int j)
{
diff --git a/gcc/testsuite/lib/target-supports.exp
b/gcc/testsuite/lib/target-supports.exp
index edd1290bd9e..79f25e3cee3 100644
--- a/gcc/testsuite/lib/target-supports.exp
+++ b/gcc/testsuite/lib/target-supports.exp
@@ -15134,3 +15134,25 @@ proc check_effective_target_memtag_exec {} {
}
return 1;
}
+
+# Return 1 if the target runtime can deref null, 0 otherwise.
+# Cache the result.
+
+proc check_effective_target_can_deref_null { } {
+ return [check_runtime can_deref_null {
+ #include <stddef.h>
+ __attribute__((noipa)) static volatile int *
+ get_null (void)
+ {
+ return (volatile int *) NULL;
+ }
+
+ int main ()
+ {
+ volatile int *p = get_null ();
+ int x = *p;
+ (void) x;
+ return 0;
+ }
+ } "-O0"]
+}
That's pretty close to what I would have written, which would have been
something like
char __attribute__((noipa))
read_mem (volatile char *p)
{
return *p;
}
int main ()
{
read_mem (NULL);
_exit (0);
}
and then, to be on the safe side, add -fno-delete-null-pointer-checks
and -Wno-null-dereference to the flags.
R.
