Hi.
So this is a patch candidate for the .gnu.lto_.lto ELF section.
As mentioned, the section contains information about bytecode version,
compression algorithm used and slim LTO object flag.
One minor issues is that I need to append random suffix to the section:
[ 6] .gnu.lto_.lto.36e74acfb145b04b PROGBITS 0000000000000000 000086
000008 00 E 0 0 1
That's because of in WPA we load more object files and the hash is used for
mapping.
Is the idea of the patch right?
Martin
>From ec550463df26855982b7b70393766cc8e7c6cc8e Mon Sep 17 00:00:00 2001
From: Martin Liska <mli...@suse.cz>
Date: Fri, 21 Jun 2019 12:14:04 +0200
Subject: [PATCH] Add .gnu.lto_.lto section.
---
gcc/lto-section-in.c | 9 +++------
gcc/lto-section-out.c | 2 --
gcc/lto-streamer-out.c | 40 +++++++++++++++++++++++++---------------
gcc/lto-streamer.h | 25 +++++++++++++++++++++----
gcc/lto/lto-common.c | 15 +++++++++++++++
5 files changed, 64 insertions(+), 27 deletions(-)
diff --git a/gcc/lto-section-in.c b/gcc/lto-section-in.c
index 4cfc0cad4be..4e7d1181f23 100644
--- a/gcc/lto-section-in.c
+++ b/gcc/lto-section-in.c
@@ -52,10 +52,10 @@ const char *lto_section_name[LTO_N_SECTION_TYPES] =
"icf",
"offload_table",
"mode_table",
- "hsa"
+ "hsa",
+ "lto"
};
-
/* Hooks so that the ipa passes can call into the lto front end to get
sections. */
@@ -146,7 +146,7 @@ lto_get_section_data (struct lto_file_decl_data *file_data,
/* WPA->ltrans streams are not compressed with exception of function bodies
and variable initializers that has been verbatim copied from earlier
compilations. */
- if (!flag_ltrans || decompress)
+ if ((!flag_ltrans || decompress) && section_type != LTO_section_lto)
{
/* Create a mapping header containing the underlying data and length,
and prepend this to the uncompression buffer. The uncompressed data
@@ -167,9 +167,6 @@ lto_get_section_data (struct lto_file_decl_data *file_data,
data = buffer.data + header_length;
}
- lto_check_version (((const lto_header *)data)->major_version,
- ((const lto_header *)data)->minor_version,
- file_data->file_name);
return data;
}
diff --git a/gcc/lto-section-out.c b/gcc/lto-section-out.c
index c91e58f0465..7ae102164ef 100644
--- a/gcc/lto-section-out.c
+++ b/gcc/lto-section-out.c
@@ -285,8 +285,6 @@ lto_destroy_simple_output_block (struct lto_simple_output_block *ob)
/* Write the header which says how to decode the pieces of the
t. */
memset (&header, 0, sizeof (struct lto_simple_header));
- header.major_version = LTO_major_version;
- header.minor_version = LTO_minor_version;
header.main_size = ob->main_stream->total_size;
lto_write_data (&header, sizeof header);
diff --git a/gcc/lto-streamer-out.c b/gcc/lto-streamer-out.c
index dc68429303c..7dee770aa11 100644
--- a/gcc/lto-streamer-out.c
+++ b/gcc/lto-streamer-out.c
@@ -1974,10 +1974,6 @@ produce_asm (struct output_block *ob, tree fn)
/* The entire header is stream computed here. */
memset (&header, 0, sizeof (struct lto_function_header));
- /* Write the header. */
- header.major_version = LTO_major_version;
- header.minor_version = LTO_minor_version;
-
if (section_type == LTO_section_function_body)
header.cfg_size = ob->cfg_stream->total_size;
header.main_size = ob->main_stream->total_size;
@@ -2270,10 +2266,6 @@ lto_output_toplevel_asms (void)
/* The entire header stream is computed here. */
memset (&header, 0, sizeof (header));
- /* Write the header. */
- header.major_version = LTO_major_version;
- header.minor_version = LTO_minor_version;
-
header.main_size = ob->main_stream->total_size;
header.string_size = ob->string_stream->total_size;
lto_write_data (&header, sizeof header);
@@ -2390,6 +2382,29 @@ prune_offload_funcs (void)
DECL_PRESERVE_P (fn_decl) = 1;
}
+/* Produce LTO section that contains global information
+ about LTO bytecode. */
+
+static void
+produce_lto_section ()
+{
+ /* Stream LTO meta section. */
+ output_block *ob = create_output_block (LTO_section_lto);
+
+ char * section_name = lto_get_section_name (LTO_section_lto, NULL, NULL);
+ lto_begin_section (section_name, false);
+ free (section_name);
+
+ lto_compression compression = ZLIB;
+
+ bool slim_object = flag_generate_lto && !flag_fat_lto_objects;
+ lto_section s
+ = { LTO_major_version, LTO_minor_version, slim_object, compression, 0 };
+ lto_write_data (&s, sizeof s);
+ lto_end_section ();
+ destroy_output_block (ob);
+}
+
/* Main entry point from the pass manager. */
void
@@ -2412,6 +2427,8 @@ lto_output (void)
/* Initialize the streamer. */
lto_streamer_init ();
+ produce_lto_section ();
+
n_nodes = lto_symtab_encoder_size (encoder);
/* Process only the functions with bodies. */
for (i = 0; i < n_nodes; i++)
@@ -2827,10 +2844,6 @@ lto_write_mode_table (void)
struct lto_simple_header_with_strings header;
memset (&header, 0, sizeof (header));
- /* Write the header. */
- header.major_version = LTO_major_version;
- header.minor_version = LTO_minor_version;
-
header.main_size = ob->main_stream->total_size;
header.string_size = ob->string_stream->total_size;
lto_write_data (&header, sizeof header);
@@ -2901,9 +2914,6 @@ produce_asm_for_decls (void)
lto_output_decl_state_streams (ob, fn_out_state);
}
- header.major_version = LTO_major_version;
- header.minor_version = LTO_minor_version;
-
/* Currently not used. This field would allow us to preallocate
the globals vector, so that it need not be resized as it is extended. */
header.num_nodes = -1;
diff --git a/gcc/lto-streamer.h b/gcc/lto-streamer.h
index 3b1e07b4bfc..2f481aebeb2 100644
--- a/gcc/lto-streamer.h
+++ b/gcc/lto-streamer.h
@@ -234,6 +234,7 @@ enum lto_section_type
LTO_section_offload_table,
LTO_section_mode_table,
LTO_section_ipa_hsa,
+ LTO_section_lto,
LTO_N_SECTION_TYPES /* Must be last. */
};
@@ -378,18 +379,31 @@ public:
unsigned int len;
};
+/* Compression algorithm used for compression of LTO bytecode. */
-/* The is the first part of the record for a function or constructor
- in the .o file. */
-struct lto_header
+enum lto_compression
+{
+ ZLIB,
+ ZSTD
+};
+
+/* Structure that represents LTO ELF section with information
+ about the format. */
+
+struct lto_section
{
int16_t major_version;
int16_t minor_version;
+ unsigned char slim_object: 1;
+ lto_compression compression: 4;
+ int32_t reserved0: 27;
};
+STATIC_ASSERT (sizeof (lto_section) == 8);
+
/* The is the first part of the record in an LTO file for many of the
IPA passes. */
-struct lto_simple_header : lto_header
+struct lto_simple_header
{
/* Size of main gimple body of function. */
int32_t main_size;
@@ -589,6 +603,9 @@ struct GTY(()) lto_file_decl_data
/* Mode translation table. */
const unsigned char *mode_table;
+
+ /* Read LTO section. */
+ lto_section lto_section_header;
};
typedef struct lto_file_decl_data *lto_file_decl_data_ptr;
diff --git a/gcc/lto/lto-common.c b/gcc/lto/lto-common.c
index 0d38ee6b57b..1cfbda0f554 100644
--- a/gcc/lto/lto-common.c
+++ b/gcc/lto/lto-common.c
@@ -2060,6 +2060,21 @@ lto_file_finalize (struct lto_file_decl_data *file_data, lto_file *file)
#else
file_data->mode_table = lto_mode_identity_table;
#endif
+
+ /* Read and verify LTO section. */
+ data = lto_get_section_data (file_data, LTO_section_lto, NULL, &len, false);
+ if (data == NULL)
+ {
+ fatal_error (input_location, "bytecode stream in file %qs generated "
+ "with GCC compiler older than 10.0", file_data->file_name);
+ return;
+ }
+
+ file_data->lto_section_header = *(const lto_section *)data;
+ lto_check_version (file_data->lto_section_header.major_version,
+ file_data->lto_section_header.minor_version,
+ file_data->file_name);
+
data = lto_get_section_data (file_data, LTO_section_decls, NULL, &len);
if (data == NULL)
{
--
2.21.0
