Re: [PATCH 3/3] lto-plugin: implement LDPT_GET_API_VERSION

["Martin Liška" <mliska@suse.cz>]

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On 6/30/22 08:43, Rui Ueyama wrote:
> Thanks Martin for creating this patch.

You're welcome.

> 
> Here is a preliminary change for the mold side: https://github.com/rui314/mold/commit/9ad49d1c556bc963d06cca8233535183490de605 <https://github.com/rui314/mold/commit/9ad49d1c556bc963d06cca8233535183490de605>
> 
> Overall the API is looking fine,

Good then!

> though it is not clear what kind of value is expected as a linker version. A linker version is not a single unsigned integer but something like "1.3.0". Something like "1.3.0-rc2" can also be a linker version. So I don't think we can represent a linker version as a single integer.

Well, you can use the same what we use GCC_VERSION (plugin_version):

1000 * MAJOR + MINOR

Let me adjust the documentation of the API.

Richi: May I install the patch?

Thanks,
Martin

> 
> On Mon, Jun 20, 2022 at 9:01 PM Martin Liška <mliska@suse.cz <mailto:mliska@suse.cz>> wrote:
> 
>     On 6/20/22 11:35, Richard Biener wrote:
>     > I think this is OK.  Can we get buy-in from mold people?
> 
>     Sure, I've just pinged Rui:
>     https://github.com/rui314/mold/issues/454#issuecomment-1160419030 <https://github.com/rui314/mold/issues/454#issuecomment-1160419030>
> 
>     Martin
> 

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From f04b187240b786a868377c3854113598ba69ce1b Mon Sep 17 00:00:00 2001
From: Martin Liska <mliska@suse.cz>
Date: Mon, 16 May 2022 14:01:52 +0200
Subject: [PATCH] lto-plugin: implement LDPT_GET_API_VERSION

include/ChangeLog:

	* plugin-api.h (enum linker_api_version): New enum.
	(ld_plugin_get_api_version): New.
	(enum ld_plugin_tag): Add LDPT_GET_API_VERSION.
	(struct ld_plugin_tv): Add tv_get_api_version.

lto-plugin/ChangeLog:

	* lto-plugin.c (negotiate_api_version): New.
	(onload): Negotiate API version.
---
 include/plugin-api.h    | 33 +++++++++++++++++++++++++++++++++
 lto-plugin/lto-plugin.c | 38 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 71 insertions(+)

diff --git a/include/plugin-api.h b/include/plugin-api.h
index 8aebe2ff267..f6402151473 100644
--- a/include/plugin-api.h
+++ b/include/plugin-api.h
@@ -483,6 +483,37 @@ enum ld_plugin_level
   LDPL_FATAL
 };
 
+/* Contract between a plug-in and a linker.  */
+
+enum linker_api_version
+{
+   /* The linker/plugin do not implement any of the API levels below, the API
+       is determined solely via the transfer vector.  */
+   LAPI_UNSPECIFIED = 0,
+
+   /* API level v1.  The linker provides get_symbols_v3, add_symbols_v2,
+      the plugin will use that and not any lower versions.
+      claim_file is thread-safe on the plugin side and
+      add_symbols on the linker side.  */
+   LAPI_V1 = 1
+};
+
+/* The linker's interface for API version negotiation.  A plug-in calls
+  the function (with its IDENTIFIER and VERSION), plus minimal and maximal
+  version of linker_api_version is provided.  Linker then returns selected
+  API version and provides its IDENTIFIER and VERSION.
+  Both PLUGIN_VERSION and LINKER_VERSION are in the following format:
+  1000 * MAJOR + MINOR.
+  Identifier pointers remain valid as long as the plugin is loaded.  */
+
+typedef
+enum linker_api_version
+(*ld_plugin_get_api_version) (const char *plugin_identifier, unsigned plugin_version,
+			      enum linker_api_version minimal_api_supported,
+			      enum linker_api_version maximal_api_supported,
+			      const char **linker_identifier,
+			      unsigned *linker_version);
+
 /* Values for the tv_tag field of the transfer vector.  */
 
 enum ld_plugin_tag
@@ -521,6 +552,7 @@ enum ld_plugin_tag
   LDPT_REGISTER_NEW_INPUT_HOOK,
   LDPT_GET_WRAP_SYMBOLS,
   LDPT_ADD_SYMBOLS_V2,
+  LDPT_GET_API_VERSION,
 };
 
 /* The plugin transfer vector.  */
@@ -556,6 +588,7 @@ struct ld_plugin_tv
     ld_plugin_get_input_section_size tv_get_input_section_size;
     ld_plugin_register_new_input tv_register_new_input;
     ld_plugin_get_wrap_symbols tv_get_wrap_symbols;
+    ld_plugin_get_api_version tv_get_api_version;
   } tv_u;
 };
 
diff --git a/lto-plugin/lto-plugin.c b/lto-plugin/lto-plugin.c
index 635e126946b..06e3219de75 100644
--- a/lto-plugin/lto-plugin.c
+++ b/lto-plugin/lto-plugin.c
@@ -74,6 +74,7 @@ along with this program; see the file COPYING3.  If not see
 #include "../gcc/lto/common.h"
 #include "simple-object.h"
 #include "plugin-api.h"
+#include "ansidecl.h"
 
 /* We need to use I64 instead of ll width-specifier on native Windows.
    The reason for this is that older MS-runtimes don't support the ll.  */
@@ -174,6 +175,10 @@ static ld_plugin_add_input_file add_input_file;
 static ld_plugin_add_input_library add_input_library;
 static ld_plugin_message message;
 static ld_plugin_add_symbols add_symbols, add_symbols_v2;
+static ld_plugin_get_api_version get_api_version;
+
+/* By default, use version LAPI_UNSPECIFIED if there is not negotiation.  */
+static enum linker_api_version api_version = LAPI_UNSPECIFIED;
 
 static struct plugin_file_info *claimed_files = NULL;
 static unsigned int num_claimed_files = 0;
@@ -1421,6 +1426,33 @@ process_option (const char *option)
   verbose = verbose || debug;
 }
 
+/* Negotiate linker API version.  */
+
+static void
+negotiate_api_version (void)
+{
+  const char *linker_identifier;
+  unsigned linker_version;
+
+  api_version = get_api_version ("GCC", GCC_VERSION, LAPI_UNSPECIFIED,
+				 LAPI_V1, &linker_identifier, &linker_version);
+
+  switch (api_version)
+    {
+    case LAPI_UNSPECIFIED:
+      break;
+    case LAPI_V1:
+      check (get_symbols_v3, LDPL_FATAL,
+	     "get_symbols_v3 required for API version 1");
+      check (add_symbols_v2, LDPL_FATAL,
+	     "add_symbols_v2 required for API version 1");
+      break;
+    default:
+      fprintf (stderr, "unsupported API version\n");
+      abort ();
+    }
+}
+
 /* Called by a linker after loading the plugin. TV is the transfer vector. */
 
 enum ld_plugin_status
@@ -1487,12 +1519,18 @@ onload (struct ld_plugin_tv *tv)
 	  /* We only use this to make user-friendly temp file names.  */
 	  link_output_name = p->tv_u.tv_string;
 	  break;
+	case LDPT_GET_API_VERSION:
+	  get_api_version = p->tv_u.tv_get_api_version;
+	  break;
 	default:
 	  break;
 	}
       p++;
     }
 
+  if (get_api_version)
+    negotiate_api_version ();
+
   check (register_claim_file, LDPL_FATAL, "register_claim_file not found");
   check (add_symbols, LDPL_FATAL, "add_symbols not found");
   status = register_claim_file (claim_file_handler);
-- 
2.36.1