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Introduce alternate_signal_stack RAII class

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This introduces a new RAII class that temporarily installs an
alternate signal stack (on systems that have sigaltstack); then
changes the one gdb use of sigaltstack to use this class instead.

This will be used in a later patch, when creating new threads that may
want to handle SIGSEGV.

gdb/ChangeLog
2019-11-26  Tom Tromey  <tom@tromey.com>

	* main.c (setup_alternate_signal_stack): Remove.
	(captured_main_1): Use gdb::alternate_signal_stack.
	* gdbsupport/alt-stack.h: New file.

Change-Id: I721c047ae9d51a35fd274a6dbc00a58c6440dae6
This commit is contained in:
Tom Tromey 2019-09-29 09:27:11 -06:00
parent 21987b9c06
commit c3efb96548
3 changed files with 78 additions and 24 deletions
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26
gdb/main.c
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@ -52,6 +52,7 @@
#ifdef GDBTK
#include "gdbtk/generic/gdbtk.h"
#endif
#include "gdbsupport/alt-stack.h"
/* The selected interpreter. This will be used as a set command
variable, so it should always be malloc'ed - since
@ -334,29 +335,6 @@ get_init_files (std::vector<std::string> *system_gdbinit,
*local_gdbinit = localinit;
}
/* Try to set up an alternate signal stack for SIGSEGV handlers.
This allows us to handle SIGSEGV signals generated when the
normal process stack is exhausted. If this stack is not set
up (sigaltstack is unavailable or fails) and a SIGSEGV is
generated when the normal stack is exhausted then the program
will behave as though no SIGSEGV handler was installed. */
static void
setup_alternate_signal_stack (void)
{
#ifdef HAVE_SIGALTSTACK
stack_t ss;
/* FreeBSD versions older than 11.0 use char * for ss_sp instead of
void *. This cast works with both types. */
ss.ss_sp = (char *) xmalloc (SIGSTKSZ);
ss.ss_size = SIGSTKSZ;
ss.ss_flags = 0;
sigaltstack(&ss, NULL);
#endif
}
/* Call command_loop. */
/* Prevent inlining this function for the benefit of GDB's selftests
@ -898,7 +876,7 @@ captured_main_1 (struct captured_main_args *context)
save_original_signals_state (quiet);
/* Try to set up an alternate signal stack for SIGSEGV handlers. */
setup_alternate_signal_stack ();
gdb::alternate_signal_stack signal_stack;
/* Initialize all files. */
gdb_init (gdb_program_name);