Обсуждение: [PATCH] Support static linking against LLVM

By default, PostgreSQL doesn't explicitly choose whether to link
statically or dynamically against LLVM when LLVM JIT is enabled (e.g.:
`./configure --with-llvm`).

`llvm-config` will choose to dynamically link by default.

In order to statically link, one must pass `--link-static` to
`llvm-config` when listing linker flags (`--ldflags`) and libraries
(`--libs`).

This patch enables custom flags to be passed to `llvm-config` linker
related invocations through the environment variable
`LLVM_CONFIG_LINK_ARGS`.

To statically link against LLVM it suffices, then, to call `configure`
with environment variable `LLVM_CONFIG_LINK_ARGS=--link-static`.
---
 config/llvm.m4 | 5 +++--
 configure      | 6 ++++--
 2 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/config/llvm.m4 b/config/llvm.m4
index 3a75cd8b4d..712bd3de6c 100644
--- a/config/llvm.m4
+++ b/config/llvm.m4
@@ -13,6 +13,7 @@ AC_DEFUN([PGAC_LLVM_SUPPORT],
   AC_REQUIRE([AC_PROG_AWK])
 
   AC_ARG_VAR(LLVM_CONFIG, [path to llvm-config command])
+  AC_ARG_VAR(LLVM_CONFIG_LINK_ARGS, [extra arguments for llvm-config linker related flags])
   PGAC_PATH_PROGS(LLVM_CONFIG, llvm-config llvm-config-7 llvm-config-6.0 llvm-config-5.0 llvm-config-4.0
llvm-config-3.9)
 
   # no point continuing if llvm wasn't found
@@ -52,7 +53,7 @@ AC_DEFUN([PGAC_LLVM_SUPPORT],
     esac
   done
 
-  for pgac_option in `$LLVM_CONFIG --ldflags`; do
+  for pgac_option in `$LLVM_CONFIG --ldflags $LLVM_CONFIG_LINK_ARGS`; do
     case $pgac_option in
       -L*) LDFLAGS="$LDFLAGS $pgac_option";;
     esac
@@ -84,7 +85,7 @@ AC_DEFUN([PGAC_LLVM_SUPPORT],
   # And then get the libraries that need to be linked in for the
   # selected components.  They're large libraries, we only want to
   # link them into the LLVM using shared library.
-  for pgac_option in `$LLVM_CONFIG --libs --system-libs $pgac_components`; do
+  for pgac_option in `$LLVM_CONFIG --libs --system-libs $LLVM_CONFIG_LINK_ARGS $pgac_components`; do
     case $pgac_option in
       -l*) LLVM_LIBS="$LLVM_LIBS $pgac_option";;
     esac
diff --git a/configure b/configure
index 86ffccb1ee..974b7f2d4e 100755
--- a/configure
+++ b/configure
@@ -1595,6 +1595,8 @@ Some influential environment variables:
   CXX         C++ compiler command
   CXXFLAGS    C++ compiler flags
   LLVM_CONFIG path to llvm-config command
+  LLVM_CONFIG_LINK_ARGS
+              extra arguments for llvm-config linker related flags
   CLANG       path to clang compiler to generate bitcode
   CPP         C preprocessor
   PKG_CONFIG  path to pkg-config utility
@@ -5200,7 +5202,7 @@ fi
     esac
   done
 
-  for pgac_option in `$LLVM_CONFIG --ldflags`; do
+  for pgac_option in `$LLVM_CONFIG --ldflags $LLVM_CONFIG_LINK_ARGS`; do
     case $pgac_option in
       -L*) LDFLAGS="$LDFLAGS $pgac_option";;
     esac
@@ -5232,7 +5234,7 @@ fi
   # And then get the libraries that need to be linked in for the
   # selected components.  They're large libraries, we only want to
   # link them into the LLVM using shared library.
-  for pgac_option in `$LLVM_CONFIG --libs --system-libs $pgac_components`; do
+  for pgac_option in `$LLVM_CONFIG --libs --system-libs $LLVM_CONFIG_LINK_ARGS $pgac_components`; do
     case $pgac_option in
       -l*) LLVM_LIBS="$LLVM_LIBS $pgac_option";;
     esac
-- 
2.40.1

Hi,

On 2023-08-10 14:45:47 -0500, Marcelo Juchem wrote:
> By default, PostgreSQL doesn't explicitly choose whether to link
> statically or dynamically against LLVM when LLVM JIT is enabled (e.g.:
> `./configure --with-llvm`).
> 
> `llvm-config` will choose to dynamically link by default.
> 
> In order to statically link, one must pass `--link-static` to
> `llvm-config` when listing linker flags (`--ldflags`) and libraries
> (`--libs`).
> 
> This patch enables custom flags to be passed to `llvm-config` linker
> related invocations through the environment variable
> `LLVM_CONFIG_LINK_ARGS`.
> 
> To statically link against LLVM it suffices, then, to call `configure`
> with environment variable `LLVM_CONFIG_LINK_ARGS=--link-static`.

I'm not opposed to it, but I'm not sure I see much need for it either. Do you
have a specific use case for this?

Greetings,

Andres Freund

Hi,

On 2023-08-11 12:59:27 -0500, Marcelo Juchem wrote:
> In my case, my product has a very controlled environment.
> We build all our infrastructure from source and we avoid dynamic linking by
> design, except where technically not viable (e.g.: pgsql extensions).
> 
> LLVM is one of the libraries we're specifically required to statically link.
> Unfortunately I can't share the specifics of why that's the case.

If you build llvm with just static lib support it should work as-is?


> On a side note, I'd like to take this opportunity to ask you if there's any
> work being done towards migrating away from deprecated LLVM APIs.
> If there's no work being done on that front, I might take a stab at it if
> there's any interest from the PostgreSQL community in that contribution.

Yes: https://postgr.es/m/CA%2BhUKGKNX_%3Df%2B1C4r06WETKTq0G4Z_7q4L4Fxn5WWpMycDj9Fw%40mail.gmail.com


> Migrating to the new APIs will have PostgreSQL require at the minimum
> version 8 of LLVM (released in March 2019).

I think Thomas' patch abstract it enough so that older versions continue to
work...

Greetings,

Andres Freund