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authorNick Alcock <nick.alcock@oracle.com>2020-06-05 23:18:06 +0100
committerNick Alcock <nick.alcock@oracle.com>2020-07-22 18:03:57 +0100
commit5dba6f05b7ba3d0e1c99da54592815564c782b39 (patch)
tree61183e2ed21e7b52a7f8540a844f2208cb6e28b9 /ld
parentf320bba50ff0aab7ce342ab9e3d25f49fc45d468 (diff)
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ld: new options --ctf-variables and --ctf-share-types
libctf recently changed to make it possible to not emit the CTF variables section. Make this the default for ld: the variables section is a simple name -> type mapping, and the names can be quite voluminous. Nothing in the variables section appears in the symbol table, by definition, so GDB cannot make use of them: special-purpose projects that implement their own analogues of symbol table lookup can do so, but they'll need to tell the linker to emit the variables section after all. The new --ctf-variables option does this. The --ctf-share-types option (valid values "share-duplicated" and "share-unconflicted") allow the caller to specify the CTF link mode. Most users will want share-duplicated, since it allows for more convenient debugging: but very large projects composed of many decoupled components may want to use share-unconflicted mode, which places types that appear in only one TU into per-TU dicts. (They may also want to relink the CTF using the ctf_link API and cu-mapping, to make their "components" larger than a single TU. Right now the linker does not expose the CU-mapping machinery. Perhaps it should in future to make this use case easier.) For now, giving the linker the ability to emit share-duplicated CTF lets us add testcases for that mode to the testsuite. ld/ * ldlex.h (option_values) <OPTION_CTF_VARIABLES, OPTION_NO_CTF_VARIABLES, OPTION_CTF_SHARE_TYPES>: New. * ld.h (ld_config_type) <ctf_variables, ctf_share_duplicated>: New fields. * ldlang.c (lang_merge_ctf): Use them. * lexsup.c (ld_options): Add ctf-variables, no-ctf-variables, ctf-share-types. (parse_args) <OPTION_CTF_VARIABLES, OPTION_NO_CTF_VARIABLES, OPTION_CTF_SHARE_TYPES>: New cases. * ld.texi: Document new options. * NEWS: Likewise.
Diffstat (limited to 'ld')
-rw-r--r--ld/ChangeLog14
-rw-r--r--ld/NEWS10
-rw-r--r--ld/ld.h8
-rw-r--r--ld/ld.texi34
-rw-r--r--ld/ldlang.c10
-rw-r--r--ld/ldlex.h3
-rw-r--r--ld/lexsup.c29
7 files changed, 107 insertions, 1 deletions
diff --git a/ld/ChangeLog b/ld/ChangeLog
index 02ce249..b45da76 100644
--- a/ld/ChangeLog
+++ b/ld/ChangeLog
@@ -1,3 +1,17 @@
+2020-07-22 Nick Alcock <nick.alcock@oracle.com>
+
+ * ldlex.h (option_values) <OPTION_CTF_VARIABLES,
+ OPTION_NO_CTF_VARIABLES, OPTION_CTF_SHARE_TYPES>: New.
+ * ld.h (ld_config_type) <ctf_variables, ctf_share_duplicated>:
+ New fields.
+ * ldlang.c (lang_merge_ctf): Use them.
+ * lexsup.c (ld_options): Add ctf-variables, no-ctf-variables,
+ ctf-share-types.
+ (parse_args) <OPTION_CTF_VARIABLES, OPTION_NO_CTF_VARIABLES,
+ OPTION_CTF_SHARE_TYPES>: New cases.
+ * ld.texi: Document new options.
+ * NEWS: Likewise.
+
2020-07-22 Egeyar Bagcioglu <egeyar.bagcioglu@oracle.com>
* ldlang.c (lang_merge_ctf): Turn errors into warnings.
diff --git a/ld/NEWS b/ld/NEWS
index eb2cff1..0fea911 100644
--- a/ld/NEWS
+++ b/ld/NEWS
@@ -1,5 +1,15 @@
-*- text -*-
+* The linker now deduplicates the types in .ctf sections. The new
+ command-line option --ctf-share-types describes how to do this:
+ its default value, share-unconflicted, produces the most compact
+ output.
+
+* The linker now omits the "variable section" from .ctf sections by
+ default, saving space. This is almost certainly what you want
+ unless you are working on a project that has its own analogue
+ of symbol tables that are not reflected in the ELF symtabs.
+
Changes in 2.35:
* X86 NaCl target support is removed.
diff --git a/ld/ld.h b/ld/ld.h
index 1790dc8..7f7d716 100644
--- a/ld/ld.h
+++ b/ld/ld.h
@@ -302,6 +302,14 @@ typedef struct
/* If set, print discarded sections in map file output. */
bfd_boolean print_map_discarded;
+
+ /* If set, emit the names and types of statically-linked variables
+ into the CTF. */
+ bfd_boolean ctf_variables;
+
+ /* If set, share only duplicated types in CTF, rather than sharing
+ all types that are not in conflict. */
+ bfd_boolean ctf_share_duplicated;
} ld_config_type;
extern ld_config_type config;
diff --git a/ld/ld.texi b/ld/ld.texi
index 2a93e94..b9b331b 100644
--- a/ld/ld.texi
+++ b/ld/ld.texi
@@ -1612,6 +1612,40 @@ definition. If the symbol is defined as a common value then any files
where this happens appear next. Finally any files that reference the
symbol are listed.
+@cindex ctf variables
+@kindex --ctf-variables
+@kindex --no-ctf-variables
+@item --ctf-variables
+@item --no-ctf-variables
+The CTF debuginfo format supports a section which encodes the names and
+types of variables found in the program which do not appear in any symbol
+table. These variables clearly cannot be looked up by address by
+conventional debuggers, so the space used for their types and names is
+usually wasted: the types are usually small but the names are often not.
+@option{--ctf-variables} causes the generation of such a section.
+The default behaviour can be restored with @option{--no-ctf-variables}.
+
+@cindex ctf type sharing
+@kindex --ctf-share-types
+@item --ctf-share-types=@var{method}
+Adjust the method used to share types between translation units in CTF.
+
+@table @samp
+@item share-unconflicted
+Put all types that do not have ambiguous definitions into the shared dictionary,
+where debuggers can easily access them, even if they only occur in one
+translation unit. This is the default.
+
+@item share-duplicated
+Put only types that occur in multiple translation units into the shared
+dictionary: types with only one definition go into per-translation-unit
+dictionaries. Types with ambiguous definitions in multiple translation units
+always go into per-translation-unit dictionaries. This tends to make the CTF
+larger, but may reduce the amount of CTF in the shared dictionary. For very
+large projects this may speed up opening the CTF and save memory in the CTF
+consumer at runtime.
+@end table
+
@cindex common allocation
@kindex --no-define-common
@item --no-define-common
diff --git a/ld/ldlang.c b/ld/ldlang.c
index b0231a1..bf29144 100644
--- a/ld/ldlang.c
+++ b/ld/ldlang.c
@@ -3755,6 +3755,7 @@ static void
lang_merge_ctf (void)
{
asection *output_sect;
+ int flags = 0;
if (!ctf_output)
return;
@@ -3791,7 +3792,14 @@ lang_merge_ctf (void)
}
}
- if (ctf_link (ctf_output, CTF_LINK_SHARE_UNCONFLICTED) < 0)
+ if (!config.ctf_share_duplicated)
+ flags = CTF_LINK_SHARE_UNCONFLICTED;
+ else
+ flags = CTF_LINK_SHARE_DUPLICATED;
+ if (!config.ctf_variables)
+ flags |= CTF_LINK_OMIT_VARIABLES_SECTION;
+
+ if (ctf_link (ctf_output, flags) < 0)
{
einfo (_("%P: warning: CTF linking failed; "
"output will have no CTF section: `%s'\n"),
diff --git a/ld/ldlex.h b/ld/ldlex.h
index 5ea083e..6eac75c 100644
--- a/ld/ldlex.h
+++ b/ld/ldlex.h
@@ -155,6 +155,9 @@ enum option_values
OPTION_NON_CONTIGUOUS_REGIONS,
OPTION_NON_CONTIGUOUS_REGIONS_WARNINGS,
OPTION_DEPENDENCY_FILE,
+ OPTION_CTF_VARIABLES,
+ OPTION_NO_CTF_VARIABLES,
+ OPTION_CTF_SHARE_TYPES,
};
/* The initial parser states. */
diff --git a/ld/lexsup.c b/ld/lexsup.c
index a79bec0..2c2d0fc 100644
--- a/ld/lexsup.c
+++ b/ld/lexsup.c
@@ -572,6 +572,18 @@ static const struct ld_option ld_options[] =
{ {"no-print-map-discarded", no_argument, NULL, OPTION_NO_PRINT_MAP_DISCARDED},
'\0', NULL, N_("Do not show discarded sections in map file output"),
TWO_DASHES },
+ { {"ctf-variables", no_argument, NULL, OPTION_CTF_VARIABLES},
+ '\0', NULL, N_("Emit names and types of static variables in CTF"),
+ TWO_DASHES },
+ { {"no-ctf-variables", no_argument, NULL, OPTION_NO_CTF_VARIABLES},
+ '\0', NULL, N_("Do not emit names and types of static variables in CTF"),
+ TWO_DASHES },
+ { {"ctf-share-types=<method>", required_argument, NULL,
+ OPTION_CTF_SHARE_TYPES},
+ '\0', NULL, N_("How to share CTF types between translation units.\n"
+ " <method> is: share-unconflicted (default),\n"
+ " share-duplicated"),
+ TWO_DASHES },
};
#define OPTION_COUNT ARRAY_SIZE (ld_options)
@@ -1637,6 +1649,23 @@ parse_args (unsigned argc, char **argv)
case OPTION_DEPENDENCY_FILE:
config.dependency_file = optarg;
break;
+
+ case OPTION_CTF_VARIABLES:
+ config.ctf_variables = TRUE;
+ break;
+
+ case OPTION_NO_CTF_VARIABLES:
+ config.ctf_variables = FALSE;
+ break;
+
+ case OPTION_CTF_SHARE_TYPES:
+ if (strcmp (optarg, "share-unconflicted") == 0)
+ config.ctf_share_duplicated = FALSE;
+ else if (strcmp (optarg, "share-duplicated") == 0)
+ config.ctf_share_duplicated = TRUE;
+ else
+ einfo (_("%F%P: bad --ctf-share-types option: %s\n"), optarg);
+ break;
}
}