Make EXEC_BACKEND more convenient on Linux and FreeBSD.

Try to disable ASLR when building in EXEC_BACKEND mode, to avoid random
memory mapping failures while testing.  For developer use only, no
effect on regular builds.

This has been originally applied as of f3e7806 for v15~, but
recently-added buildfarm member gokiburi tests this configuration on
older branches as well, causing it to fail randomly as ASLR would be
enabled.

Suggested-by: Andres Freund <andres@anarazel.de>
Tested-by: Bossart, Nathan <bossartn@amazon.com>
Discussion: https://postgr.es/m/20210806032944.m4tz7j2w47mant26%40alap3.anarazel.de
Backpatch-through: 12

6 files changed, 50 insertions, 0 deletions

diff --git a/src/bin/pg_ctl/pg_ctl.c b/src/bin/pg_ctl/pg_ctl.c
index 8ab9ecb78f6..01b815d4a07 100644
--- a/src/bin/pg_ctl/pg_ctl.c
+++ b/src/bin/pg_ctl/pg_ctl.c
@@ -453,6 +453,10 @@ start_postmaster(void)
 	fflush(stdout);
 	fflush(stderr);
 
+#ifdef EXEC_BACKEND
+	pg_disable_aslr();
+#endif
+
 	pm_pid = fork();
 	if (pm_pid < 0)
 	{
diff --git a/src/common/exec.c b/src/common/exec.c
index 8f1147b68a0..7f0142fb475 100644
--- a/src/common/exec.c
+++ b/src/common/exec.c
@@ -25,6 +25,14 @@
 #include <sys/wait.h>
 #include <unistd.h>
 
+#ifdef EXEC_BACKEND
+#if defined(HAVE_SYS_PERSONALITY_H)
+#include <sys/personality.h>
+#elif defined(HAVE_SYS_PROCCTL_H)
+#include <sys/procctl.h>
+#endif
+#endif
+
 /* Inhibit mingw CRT's auto-globbing of command line arguments */
 #if defined(WIN32) && !defined(_MSC_VER)
 extern int _CRT_glob = 0; /* 0 turns off globbing; 1 turns it on */
@@ -492,6 +500,31 @@ set_pglocale_pgservice(const char *argv0, const char *app)
 	}
 }
 
+#ifdef EXEC_BACKEND
+/*
+ * For the benefit of PostgreSQL developers testing EXEC_BACKEND on Unix
+ * systems (code paths normally exercised only on Windows), provide a way to
+ * disable address space layout randomization, if we know how on this platform.
+ * Otherwise, backends may fail to attach to shared memory at the fixed address
+ * chosen by the postmaster.  (See also the macOS-specific hack in
+ * sysv_shmem.c.)
+ */
+int
+pg_disable_aslr(void)
+{
+#if defined(HAVE_SYS_PERSONALITY_H)
+	return personality(ADDR_NO_RANDOMIZE);
+#elif defined(HAVE_SYS_PROCCTL_H) && defined(PROC_ASLR_FORCE_DISABLE)
+	int			data = PROC_ASLR_FORCE_DISABLE;
+
+	return procctl(P_PID, 0, PROC_ASLR_CTL, &data);
+#else
+	errno = ENOSYS;
+	return -1;
+#endif
+}
+#endif
+
 #ifdef WIN32
 
 /*
diff --git a/src/include/pg_config.h.in b/src/include/pg_config.h.in
index 2711c2ce9bd..2cd221b85a0 100644
--- a/src/include/pg_config.h.in
+++ b/src/include/pg_config.h.in
@@ -590,6 +590,9 @@
 /* Define to 1 if you have the <sys/ipc.h> header file. */
 #undef HAVE_SYS_IPC_H
 
+/* Define to 1 if you have the <sys/personality.h> header file. */
+#undef HAVE_SYS_PERSONALITY_H
+
 /* Define to 1 if you have the <sys/prctl.h> header file. */
 #undef HAVE_SYS_PRCTL_H
 
diff --git a/src/include/port.h b/src/include/port.h
index 0c3c8d14e76..70b193657e4 100644
--- a/src/include/port.h
+++ b/src/include/port.h
@@ -115,6 +115,11 @@ extern char *pipe_read_line(char *cmd, char *line, int maxsize);
 /* Doesn't belong here, but this is used with find_other_exec(), so... */
 #define PG_BACKEND_VERSIONSTR "postgres (PostgreSQL) " PG_VERSION "\n"
 
+#ifdef EXEC_BACKEND
+/* Disable ASLR before exec, for developer builds only (in exec.c) */
+extern int pg_disable_aslr(void);
+#endif
+
 
 #if defined(WIN32) || defined(__CYGWIN__)
 #define EXE ".exe"
diff --git a/src/test/regress/pg_regress.c b/src/test/regress/pg_regress.c
index 25683a78413..36cc1707bfa 100644
--- a/src/test/regress/pg_regress.c
+++ b/src/test/regress/pg_regress.c
@@ -1191,6 +1191,10 @@ spawn_process(const char *cmdline)
 	if (logfile)
 		fflush(logfile);
 
+#ifdef EXEC_BACKEND
+	pg_disable_aslr();
+#endif
+
 	pid = fork();
 	if (pid == -1)
 	{
diff --git a/src/tools/msvc/Solution.pm b/src/tools/msvc/Solution.pm
index 243d0b64fd0..4147e8ad260 100644
--- a/src/tools/msvc/Solution.pm
+++ b/src/tools/msvc/Solution.pm
@@ -380,6 +380,7 @@ sub GenerateFiles
 		HAVE_SYS_EPOLL_H                         => undef,
 		HAVE_SYS_EVENT_H                         => undef,
 		HAVE_SYS_IPC_H                           => undef,
+		HAVE_SYS_PERSONALITY_H                   => undef,
 		HAVE_SYS_PRCTL_H                         => undef,
 		HAVE_SYS_PROCCTL_H                       => undef,
 		HAVE_SYS_PSTAT_H                         => undef,