Avoid passing function pointers across process boundaries.

We'd already recognized that we can't pass function pointers across process
boundaries for functions in loadable modules, since a shared library could
get loaded at different addresses in different processes.  But actually the
practice doesn't work for functions in the core backend either, if we're
using EXEC_BACKEND.  This is the cause of recent failures on buildfarm
member culicidae.  Switch to passing a string function name in all cases.

Something like this needs to be back-patched into 9.6, but let's see
if the buildfarm likes it first.

Petr Jelinek, with a bunch of basically-cosmetic adjustments by me

Discussion: https://postgr.es/m/[email protected]

2 files changed, 11 insertions, 6 deletions

diff --git a/src/backend/utils/fmgr/dfmgr.c b/src/backend/utils/fmgr/dfmgr.c
index 94d7dac94ce..9739c4c1447 100644
--- a/src/backend/utils/fmgr/dfmgr.c
+++ b/src/backend/utils/fmgr/dfmgr.c
@@ -91,7 +91,7 @@ static const Pg_magic_struct magic_data = PG_MODULE_MAGIC_DATA;
  * at less cost than repeating load_external_function.
  */
 PGFunction
-load_external_function(char *filename, char *funcname,
+load_external_function(const char *filename, const char *funcname,
 					   bool signalNotFound, void **filehandle)
 {
 	char	   *fullname;
@@ -108,8 +108,12 @@ load_external_function(char *filename, char *funcname,
 	if (filehandle)
 		*filehandle = lib_handle;
 
-	/* Look up the function within the library */
-	retval = (PGFunction) pg_dlsym(lib_handle, funcname);
+	/*
+	 * Look up the function within the library.  According to POSIX dlsym()
+	 * should declare its second argument as "const char *", but older
+	 * platforms might not, so for the time being we just cast away const.
+	 */
+	retval = (PGFunction) pg_dlsym(lib_handle, (char *) funcname);
 
 	if (retval == NULL && signalNotFound)
 		ereport(ERROR,
@@ -155,9 +159,10 @@ load_file(const char *filename, bool restricted)
  * Return (PGFunction) NULL if not found.
  */
 PGFunction
-lookup_external_function(void *filehandle, char *funcname)
+lookup_external_function(void *filehandle, const char *funcname)
 {
-	return (PGFunction) pg_dlsym(filehandle, funcname);
+	/* as above, cast away const for the time being */
+	return (PGFunction) pg_dlsym(filehandle, (char *) funcname);
 }
 
 
diff --git a/src/backend/utils/fmgr/fmgr.c b/src/backend/utils/fmgr/fmgr.c
index 68d2110890a..d9e3bf240db 100644
--- a/src/backend/utils/fmgr/fmgr.c
+++ b/src/backend/utils/fmgr/fmgr.c
@@ -381,7 +381,7 @@ fmgr_info_other_lang(Oid functionId, FmgrInfo *finfo, HeapTuple procedureTuple)
  * pg_proc.
  */
 const Pg_finfo_record *
-fetch_finfo_record(void *filehandle, char *funcname)
+fetch_finfo_record(void *filehandle, const char *funcname)
 {
 	char	   *infofuncname;
 	PGFInfoFunction infofunc;