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Disable spurious -Wstringop-overflow for setjmp/longjmp (bug 26647)

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Building glibc with GCC 11 fails with (among other warnings) spurious
-Wstringop-overflow warnings from calls to setjmp and longjmp with a
pointer to a pthread_unwind_buf that is smaller than jmp_buf.  As
discussed in bug 26647, the warning in libc-start.c is a false
positive, because setjmp and longjmp do not access anything (the
signal mask) beyond the common prefix of the two structures, so this
patch disables the warning for that call to setjmp, as well as for two
calls in NPTL code that produce the same warning and look like false
positives for the same reason.

Tested with build-many-glibcs.py for arm-linux-gnueabi, where this
allows the build to get further.

Reviewed-by: DJ Delorie <dj@redhat.com>
This commit is contained in:
Joseph Myers 2020-10-30 21:38:31 +00:00
parent 961d12d947
commit 2098d4034d
3 changed files with 30 additions and 0 deletions
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10
csu/libc-start.c
View File

@ -21,6 +21,7 @@
#include <unistd.h>
#include <ldsodefs.h>
#include <exit-thread.h>
#include <libc-diag.h>
#include <libc-internal.h>
#include <elf/libc-early-init.h>
#include <stdbool.h>
@ -298,7 +299,16 @@ LIBC_START_MAIN (int (*main) (int, char **, char ** MAIN_AUXVEC_DECL),
struct pthread_unwind_buf unwind_buf;
int not_first_call;
DIAG_PUSH_NEEDS_COMMENT;
#if __GNUC_PREREQ (7, 0)
/* This call results in a -Wstringop-overflow warning because struct
pthread_unwind_buf is smaller than jmp_buf. setjmp and longjmp
do not use anything beyond the common prefix (they never access
the saved signal mask), so that is a false positive. */
DIAG_IGNORE_NEEDS_COMMENT (11, "-Wstringop-overflow=");
#endif
not_first_call = setjmp ((struct __jmp_buf_tag *) unwind_buf.cancel_jmp_buf);
DIAG_POP_NEEDS_COMMENT;
if (__glibc_likely (! not_first_call))
{
struct pthread *self = THREAD_SELF;

10
nptl/pthread_create.c
View File

@ -26,6 +26,7 @@
#include <hp-timing.h>
#include <ldsodefs.h>
#include <atomic.h>
#include <libc-diag.h>
#include <libc-internal.h>
#include <resolv.h>
#include <kernel-features.h>
@ -400,7 +401,16 @@ START_THREAD_DEFN
struct pthread_unwind_buf unwind_buf;
int not_first_call;
DIAG_PUSH_NEEDS_COMMENT;
#if __GNUC_PREREQ (7, 0)
/* This call results in a -Wstringop-overflow warning because struct
pthread_unwind_buf is smaller than jmp_buf. setjmp and longjmp
do not use anything beyond the common prefix (they never access
the saved signal mask), so that is a false positive. */
DIAG_IGNORE_NEEDS_COMMENT (11, "-Wstringop-overflow=");
#endif
not_first_call = setjmp ((struct __jmp_buf_tag *) unwind_buf.cancel_jmp_buf);
DIAG_POP_NEEDS_COMMENT;
/* No previous handlers. NB: This must be done after setjmp since the
private space in the unwind jump buffer may overlap space used by

10
nptl/unwind.c
View File

@ -23,6 +23,7 @@
#include <string.h>
#include <unistd.h>
#include "pthreadP.h"
#include <libc-diag.h>
#include <jmpbuf-unwind.h>
#ifdef _STACK_GROWS_DOWN
@ -90,8 +91,17 @@ unwind_stop (int version, _Unwind_Action actions,
}
}
DIAG_PUSH_NEEDS_COMMENT;
#if __GNUC_PREREQ (7, 0)
/* This call results in a -Wstringop-overflow warning because struct
pthread_unwind_buf is smaller than jmp_buf. setjmp and longjmp
do not use anything beyond the common prefix (they never access
the saved signal mask), so that is a false positive. */
DIAG_IGNORE_NEEDS_COMMENT (11, "-Wstringop-overflow=");
#endif
if (do_longjump)
__libc_unwind_longjmp ((struct __jmp_buf_tag *) buf->cancel_jmp_buf, 1);
DIAG_POP_NEEDS_COMMENT;
return _URC_NO_REASON;
}