On 2020-03-30 12:06 p.m., David Malcolm wrote:
It's a double-free bug in lra.c, albeit one that requires being used
in a multithreaded way from libgccjit to be triggered.
libgccjit's test-threads.c repeatedly compiles and runs numerous tests,
each in a separate thread.
Attempting to add an empty test that generates no code leads to a
double-free ICE within that thread, within lra.c's
finish_insn_code_data_once.
The root cause is that the insn_code_data array is cleared in
init_insn_code_data_once, but this is only called the first time
a cgraph_node is expanded [1], whereas the "loop-over-all-elements
and free them" is unconditionally called in finalize [2]. Hence
if there are no functions:
* the array is not re-initialized for the empty context
* when finish_insn_code_data_once is called for the empty context
it still contains the freed pointers from the previous context
that held the jit mutex, and hence the free is a double-free.
This patch sets the pointers to NULL after freeing them, fixing
the ICE. The calls to free are still guarded by a check for NULL,
which is redundant, but maybe there's a reason for not wanting to
call "free" on a possibly-NULL value many times on process exit?
(it makes the diff cleaner, at least)
Fixes the issue in jit.dg.
Full bootstrap & regression test in progress.
Is it OK for master if it passes?
Sure, David. Thank you for the patch.
gcc/ChangeLog:
* lra.c (finish_insn_code_data_once): Set the array elements
to NULL after freeing them.
gcc/testsuite/ChangeLog:
* jit.dg/all-non-failing-tests.h: Add test-empty.c
---
gcc/lra.c | 5 ++++-
gcc/testsuite/jit.dg/all-non-failing-tests.h | 10 ++++++++++
2 files changed, 14 insertions(+), 1 deletion(-)
diff --git a/gcc/lra.c b/gcc/lra.c
index d5ea3622686..5e8b75b1fda 100644
--- a/gcc/lra.c
+++ b/gcc/lra.c
@@ -653,7 +653,10 @@ finish_insn_code_data_once (void)
for (unsigned int i = 0; i < NUM_INSN_CODES; i++)
{
if (insn_code_data[i] != NULL)
- free (insn_code_data[i]);
+ {
+ free (insn_code_data[i]);
+ insn_code_data[i] = NULL;
+ }
}
}
diff --git a/gcc/testsuite/jit.dg/all-non-failing-tests.h b/gcc/testsuite/jit.dg/all-non-failing-tests.h
index b2acc74ae95..af744192a73 100644
--- a/gcc/testsuite/jit.dg/all-non-failing-tests.h
+++ b/gcc/testsuite/jit.dg/all-non-failing-tests.h
@@ -116,6 +116,13 @@
#undef create_code
#undef verify_code
+/* test-empty.c */
+#define create_code create_code_empty
+#define verify_code verify_code_empty
+#include "test-empty.c"
+#undef create_code
+#undef verify_code
+
/* test-error-*.c: We don't use these test cases, since they deliberately
introduce errors, which we don't want here. */
@@ -328,6 +335,9 @@ const struct testcase testcases[] = {
{"expressions",
create_code_expressions,
verify_code_expressions},
+ {"empty",
+ create_code_empty,
+ verify_code_empty},
{"factorial",
create_code_factorial,
verify_code_factorial},
