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* [glibc] Avoid -Wstringop-overflow warning in pthread_cleanup_push macros
@ 2020-10-30 22:30 Joseph Myers
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From: Joseph Myers @ 2020-10-30 22:30 UTC (permalink / raw)
To: glibc-cvs
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=548f467fa14ffe7d955beeb31b30e2aeae4467e0
commit 548f467fa14ffe7d955beeb31b30e2aeae4467e0
Author: Joseph Myers <joseph@codesourcery.com>
Date: Fri Oct 30 22:25:42 2020 +0000
Avoid -Wstringop-overflow warning in pthread_cleanup_push macros
GCC 11 introduces a -Wstringop-overflow warning for calls to functions
with an array argument passed as a pointer to memory not large enough
for that array. This includes the __sigsetjmp calls from
pthread_cleanup_push macros, because those use a structure in
__pthread_unwind_buf_t, which has a common initial subsequence with
jmp_buf but does not include the saved signal mask; this is OK in this
case because the second argument to __sigsetjmp is 0 so the signal
mask is not accessed.
To avoid this warning, use a function alias __sigsetjmp_cancel with
first argument an array of exactly the type used in the calls to the
function, if using GCC 11 or later. With older compilers, continue to
use __sigsetjmp with a cast, to avoid any issues with compilers
predating the returns_twice attribute not applying the same special
handling to __sigsetjmp_cancel as to __sigsetjmp.
Tested with build-many-glibcs.py for arm-linux-gnueabi that this fixes
the testsuite build failures.
Diff:
---
misc/sys/cdefs.h | 8 ++++++++
sysdeps/nptl/pthread.h | 37 +++++++++++++++++++++++++++----------
2 files changed, 35 insertions(+), 10 deletions(-)
diff --git a/misc/sys/cdefs.h b/misc/sys/cdefs.h
index 6b9763a92a..86906c2478 100644
--- a/misc/sys/cdefs.h
+++ b/misc/sys/cdefs.h
@@ -563,4 +563,12 @@ _Static_assert (0, "IEEE 128-bits long double requires redirection on this platf
# define __attr_access(x)
#endif
+/* Specify that a function such as setjmp or vfork may return
+ twice. */
+#if __GNUC_PREREQ (4, 1)
+# define __attribute_returns_twice__ __attribute__ ((__returns_twice__))
+#else
+# define __attribute_returns_twice__ /* Ignore. */
+#endif
+
#endif /* sys/cdefs.h */
diff --git a/sysdeps/nptl/pthread.h b/sysdeps/nptl/pthread.h
index d4194da776..3a34d82342 100644
--- a/sysdeps/nptl/pthread.h
+++ b/sysdeps/nptl/pthread.h
@@ -512,13 +512,15 @@ extern void pthread_testcancel (void);
/* Cancellation handling with integration into exception handling. */
+struct __cancel_jmp_buf_tag
+{
+ __jmp_buf __cancel_jmp_buf;
+ int __mask_was_saved;
+};
+
typedef struct
{
- struct
- {
- __jmp_buf __cancel_jmp_buf;
- int __mask_was_saved;
- } __cancel_jmp_buf[1];
+ struct __cancel_jmp_buf_tag __cancel_jmp_buf[1];
void *__pad[4];
} __pthread_unwind_buf_t __attribute__ ((__aligned__));
@@ -658,8 +660,8 @@ __pthread_cleanup_routine (struct __pthread_cleanup_frame *__frame)
__pthread_unwind_buf_t __cancel_buf; \
void (*__cancel_routine) (void *) = (routine); \
void *__cancel_arg = (arg); \
- int __not_first_call = __sigsetjmp ((struct __jmp_buf_tag *) (void *) \
- __cancel_buf.__cancel_jmp_buf, 0); \
+ int __not_first_call = __sigsetjmp_cancel (__cancel_buf.__cancel_jmp_buf, \
+ 0); \
if (__glibc_unlikely (__not_first_call)) \
{ \
__cancel_routine (__cancel_arg); \
@@ -693,8 +695,8 @@ extern void __pthread_unregister_cancel (__pthread_unwind_buf_t *__buf)
__pthread_unwind_buf_t __cancel_buf; \
void (*__cancel_routine) (void *) = (routine); \
void *__cancel_arg = (arg); \
- int __not_first_call = __sigsetjmp ((struct __jmp_buf_tag *) (void *) \
- __cancel_buf.__cancel_jmp_buf, 0); \
+ int __not_first_call = __sigsetjmp_cancel (__cancel_buf.__cancel_jmp_buf, \
+ 0); \
if (__glibc_unlikely (__not_first_call)) \
{ \
__cancel_routine (__cancel_arg); \
@@ -730,9 +732,24 @@ extern void __pthread_unwind_next (__pthread_unwind_buf_t *__buf)
;
#endif
-/* Function used in the macros. */
+/* Function used in the macros. Calling __sigsetjmp, with its first
+ argument declared as an array, results in a -Wstringop-overflow
+ warning from GCC 11 because struct pthread_unwind_buf is smaller
+ than jmp_buf. The calls from the macros have __SAVEMASK set to 0,
+ so nothing beyond the common prefix is used and this warning is a
+ false positive. Use an alias with its first argument declared to
+ use the type in the macros if possible to avoid this warning. */
+#if __GNUC_PREREQ (11, 0)
+extern int __REDIRECT_NTHNL (__sigsetjmp_cancel,
+ (struct __cancel_jmp_buf_tag __env[1],
+ int __savemask),
+ __sigsetjmp) __attribute_returns_twice__;
+#else
+# define __sigsetjmp_cancel(env, savemask) \
+ __sigsetjmp ((struct __jmp_buf_tag *) (void *) (env), (savemask))
extern int __sigsetjmp (struct __jmp_buf_tag __env[1],
int __savemask) __THROWNL;
+#endif
/* Mutex handling. */
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