Here is what I'm doing right now,
.
├── helloworld--1.0.sql
├── helloworld.control
├── helloworld.go
└── Makefile
helloworld.go
:
package helloworld
/*
#cgo LDFLAGS: -rdynamic
#include "postgres.h"
#include "fmgr.h"
#include "utils/builtins.h"
PG_MODULE_MAGIC;
PG_FUNCTION_INFO_V1(helloworld);
PG_FUNCTION_INFO_V1(hello_text_arg);
PG_FUNCTION_INFO_V1(hello_ereport);
Datum
hello_world(PG_FUNCTION_ARGS)
{
PG_RETURN_TEXT_P(cstring_to_text("Hello, World!"));
}
Datum
hello_text_arg(PG_FUNCTION_ARGS)
{
text *hello = cstring_to_text("Hello, ");
int32 hello_sz = VARSIZE(hello) - VARHDRSZ;
text *name = PG_GETARG_TEXT_P(0);
int32 name_sz = VARSIZE(name) - VARHDRSZ;
text *tail = cstring_to_text("!");
int32 tail_sz = VARSIZE(tail) - VARHDRSZ;
int32 out_sz = hello_sz + name_sz + tail_sz + VARHDRSZ;
text *out = (text *) palloc(out_sz);
SET_VARSIZE(out, out_sz);
memcpy(VARDATA(out), VARDATA(hello), hello_sz);
memcpy(VARDATA(out) + hello_sz, VARDATA(name), name_sz);
memcpy(VARDATA(out) + hello_sz + name_sz, VARDATA(tail), tail_sz);
PG_RETURN_TEXT_P(out);
}
Datum
hello_ereport(PG_FUNCTION_ARGS)
{
ereport(ERROR, (errcode(ERRCODE_NULL_VALUE_NOT_ALLOWED), errmsg("null value not allowed")));
PG_RETURN_VOID();
}
*/
import "C"
Makefile
:
MODULES = helloworld
EXTENSION = helloworld
DATA = helloworld--1.0.sql
PGFILEDESC = "helloworld - example extension for postgresql"
REGRESS = helloworld
PG_CONFIG = pg_config
PGXS := $(shell $(PG_CONFIG) --pgxs)
INCLUDEDIR = $(shell $(PG_CONFIG) --includedir-server)
include $(PGXS)
helloworld.so:
CGO_CFLAGS="-rdynamic -I$(INCLUDEDIR)" CGO_LDFLAGS="-rdynamic $(LDFLAGS)" go build -v -buildmode=c-shared -o helloworld.so .
It produced these errors when making :
/tmp/go-build019341122/github.com/amosbird/rpctest/helloworld/_obj/helloworld.cgo2.o: In function `hello_world':
helloworld.cgo2.c:(.text+0x48): undefined reference to `cstring_to_text'
/tmp/go-build019341122/github.com/amosbird/rpctest/helloworld/_obj/helloworld.cgo2.o: In function `hello_text_arg':
helloworld.cgo2.c:(.text+0x63): undefined reference to `cstring_to_text'
helloworld.cgo2.c:(.text+0x86): undefined reference to `pg_detoast_datum'
helloworld.cgo2.c:(.text+0xa5): undefined reference to `cstring_to_text'
helloworld.cgo2.c:(.text+0xd7): undefined reference to `palloc'
/tmp/go-build019341122/github.com/amosbird/rpctest/helloworld/_obj/helloworld.cgo2.o: In function `hello_ereport':
helloworld.cgo2.c:(.text+0x1a8): undefined reference to `errstart'
helloworld.cgo2.c:(.text+0x1bd): undefined reference to `errmsg'
helloworld.cgo2.c:(.text+0x1c9): undefined reference to `errcode'
helloworld.cgo2.c:(.text+0x1d7): undefined reference to `errfinish'
collect2: ld returned 1 exit status
make: *** [helloworld.so] Error 2
I have no idea if this would work. There are so many black magic happened here.
So the main question is, what is the correct Makefile that can be used to build a Postgres extension in cgo?
A specific question to these errors is, what can I do to defer those symbol resolution in cgo's linking process?