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include, libctf, ld: extend variable section to contain functions too
The CTF variable section is an optional (usually-not-present) section in the CTF dict which contains name -> type mappings corresponding to data symbols that are present in the linker input but not in the output symbol table: the idea is that programs that use their own symbol- resolution mechanisms can use this section to look up the types of symbols they have found using their own mechanism. Because these removed symbols (mostly static variables, functions, etc) all have names that are unlikely to appear in the ELF symtab and because very few programs have their own symbol-resolution mechanisms, a special linker flag (--ctf-variables) is needed to emit this section. Historically, we emitted only removed data symbols into the variable section. This seemed to make sense at the time, but in hindsight it really doesn't: functions are symbols too, and a C program can look them up just like any other type. So extend the variable section so that it contains all static function symbols too (if it is emitted at all), with types of kind CTF_K_FUNCTION. This is a little fiddly. We relied on compiler assistance for data symbols: the compiler simply emits all data symbols twice, once into the symtypetab as an indexed symbol and once into the variable section. Rather than wait for a suitably adjusted compiler that does the same for function symbols, we can pluck unreported function symbols out of the symtab and add them to the variable section ourselves. While we're at it, we do the same with data symbols: this is redundant right now because the compiler does it, but it costs very little time and lets the compiler drop this kludge and save a little space in .o files. include/ * ctf.h: Mention the new things we can see in the variable section. ld/ * testsuite/ld-ctf/data-func-conflicted-vars.d: New test. libctf/ * ctf-link.c (ctf_link_deduplicating_variables): Duplicate symbols into the variable section too. * ctf-serialize.c (symtypetab_delete_nonstatic_vars): Rename to... (symtypetab_delete_nonstatics): ... this. Check the funchash when pruning redundant variables. (ctf_symtypetab_sect_sizes): Adjust accordingly. * NEWS: Describe this change.
This commit is contained in:
Nick Alcock
parent
a12c988767
commit
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@ -89,13 +89,13 @@ extern "C"
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entries and reorder them accordingly (dropping the indexes in the process).
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Variable records (as distinct from data objects) provide a modicum of support
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for non-ELF systems, mapping a variable name to a CTF type ID. The variable
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names are sorted into ASCIIbetical order, permitting binary searching. We do
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not define how the consumer maps these variable names to addresses or
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for non-ELF systems, mapping a variable or function name to a CTF type ID.
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The names are sorted into ASCIIbetical order, permitting binary searching.
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We do not define how the consumer maps these variable names to addresses or
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anything else, or indeed what these names represent: they might be names
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looked up at runtime via dlsym() or names extracted at runtime by a debugger
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or anything else the consumer likes. Variable records with identically-
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named entries in the data object section are removed.
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named entries in the data object or function index section are removed.
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The data types section is a list of variable size records that represent each
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type, in order by their ID. The types themselves form a directed graph,
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69
ld/testsuite/ld-ctf/data-func-conflicted-vars.d
Normal file
69
ld/testsuite/ld-ctf/data-func-conflicted-vars.d
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@ -0,0 +1,69 @@
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#as:
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#source: data-func-1.c
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#source: data-func-2.c
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#objdump: --ctf
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#ld: -shared -s --ctf-variables
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#name: Conflicted data syms, partially indexed, stripped, with variables
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.*: +file format .*
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Contents of CTF section \.ctf:
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Header:
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Magic number: 0xdff2
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Version: 4 \(CTF_VERSION_3\)
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#...
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Data object section: .* \(0x[1-9a-f][0-9a-f]* bytes\)
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Function info section: .* \(0x[1-9a-f][0-9a-f]* bytes\)
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Object index section: .* \(0xc bytes\)
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Variable section: .* \(0x10 bytes\)
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Type section: .* \(0x118 bytes\)
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String section: .*
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#...
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Data objects:
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bar -> 0x[0-9a-f]*: \(kind 6\) struct var_3 \(size 0x[0-9a-f]*\) \(aligned at 0x[0-9a-f]*\)
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var_1 -> 0x[0-9a-f]*: \(kind 10\) foo_t \(size 0x[0-9a-f]*\) \(aligned at 0x[0-9a-f]*\) -> .*
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var_666 -> 0x[0-9a-f]*: \(kind 3\) foo_t \* \(size 0x[0-9a-f]*\) \(aligned at 0x[0-9a-f]*\) -> .*
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Function objects:
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func_[0-9]* -> 0x[0-9a-f]*: \(kind 5\) void \*\(\*\) \(const char \*restrict, int \(\*\)\(\*\) \(const char \*\)\) \(aligned at 0x[0-9a-f]*\)
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#...
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Variables:
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funcs -> .*
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other_func -> .*
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#...
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Types:
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#...
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.*: \(kind 6\) struct var_3 .*
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#...
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CTF archive member: .*/data-func-1\.c:
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Header:
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Magic number: 0xdff2
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Version: 4 \(CTF_VERSION_3\)
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#...
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Parent name: \.ctf
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Compilation unit name: .*/data-func-1\.c
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Data object section: .* \(0x[1-9a-f][0-9a-f]* bytes\)
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Type section: .* \(0xc bytes\)
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String section: .*
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Labels:
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Data objects:
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var_[0-9]* -> 0x80000001*: \(kind 10\) foo_t \(size 0x[0-9a-f]*\) \(aligned at 0x[0-9a-f]*\) -> .*
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var_[0-9]* -> 0x80000001*: \(kind 10\) foo_t \(size 0x[0-9a-f]*\) \(aligned at 0x[0-9a-f]*\) -> .*
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var_[0-9]* -> 0x80000001*: \(kind 10\) foo_t \(size 0x[0-9a-f]*\) \(aligned at 0x[0-9a-f]*\) -> .*
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var_[0-9]* -> 0x80000001*: \(kind 10\) foo_t \(size 0x[0-9a-f]*\) \(aligned at 0x[0-9a-f]*\) -> .*
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var_[0-9]* -> 0x80000001*: \(kind 10\) foo_t \(size 0x[0-9a-f]*\) \(aligned at 0x[0-9a-f]*\) -> .*
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var_[0-9]* -> 0x80000001*: \(kind 10\) foo_t \(size 0x[0-9a-f]*\) \(aligned at 0x[0-9a-f]*\) -> .*
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var_[0-9]* -> 0x80000001*: \(kind 10\) foo_t \(size 0x[0-9a-f]*\) \(aligned at 0x[0-9a-f]*\) -> .*
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var_[0-9]* -> 0x80000001*: \(kind 10\) foo_t \(size 0x[0-9a-f]*\) \(aligned at 0x[0-9a-f]*\) -> .*
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#...
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Function objects:
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Variables:
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Types:
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0x80000001: \(kind 10\) foo_t .* -> .* int .*
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#...
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@ -1,5 +1,14 @@
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-*- text -*-
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Changes in 2.39:
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* New features
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** The CTF variable section (if generated via ld --ctf-variables) now contains
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entries for static functions, hidden functions, and other functions with
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no associated symbol. The associated type is of kind CTF_K_FUNCTION.
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(No change if --ctf-variables is not specified, which is the default.)
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Changes in 2.37:
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* New features
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@ -807,7 +807,12 @@ ctf_link_deduplicating_close_inputs (ctf_dict_t *fp, ctf_dynhash_t *cu_names,
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return 0;
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}
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/* Do a deduplicating link of all variables in the inputs. */
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/* Do a deduplicating link of all variables in the inputs.
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Also, if we are not omitting the variable section, integrate all symbols from
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the symtypetabs into the variable section too. (Duplication with the
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symtypetab section in the output will be eliminated at serialization time.) */
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static int
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ctf_link_deduplicating_variables (ctf_dict_t *fp, ctf_dict_t **inputs,
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size_t ninputs, int cu_mapped)
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@ -820,6 +825,8 @@ ctf_link_deduplicating_variables (ctf_dict_t *fp, ctf_dict_t **inputs,
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ctf_id_t type;
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const char *name;
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/* First the variables on the inputs. */
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while ((type = ctf_variable_next (inputs[i], &it, &name)) != CTF_ERR)
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{
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if (ctf_link_one_variable (fp, inputs[i], name, type, cu_mapped) < 0)
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@ -830,6 +837,34 @@ ctf_link_deduplicating_variables (ctf_dict_t *fp, ctf_dict_t **inputs,
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}
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if (ctf_errno (inputs[i]) != ECTF_NEXT_END)
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return ctf_set_errno (fp, ctf_errno (inputs[i]));
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/* Next the symbols. We integrate data symbols even though the compiler
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is currently doing the same, to allow the compiler to stop in
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future. */
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while ((type = ctf_symbol_next (inputs[i], &it, &name, 0)) != CTF_ERR)
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{
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if (ctf_link_one_variable (fp, inputs[i], name, type, 1) < 0)
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{
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ctf_next_destroy (it);
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return -1; /* errno is set for us. */
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}
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}
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if (ctf_errno (inputs[i]) != ECTF_NEXT_END)
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return ctf_set_errno (fp, ctf_errno (inputs[i]));
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/* Finally the function symbols. */
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while ((type = ctf_symbol_next (inputs[i], &it, &name, 1)) != CTF_ERR)
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{
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if (ctf_link_one_variable (fp, inputs[i], name, type, 1) < 0)
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{
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ctf_next_destroy (it);
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return -1; /* errno is set for us. */
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}
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}
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if (ctf_errno (inputs[i]) != ECTF_NEXT_END)
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return ctf_set_errno (fp, ctf_errno (inputs[i]));
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}
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return 0;
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}
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@ -431,12 +431,12 @@ emit_symtypetab_index (ctf_dict_t *fp, ctf_dict_t *symfp, uint32_t *dp,
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return 0;
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}
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/* Delete data symbols that have been assigned names from the variable section.
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Must be called from within ctf_serialize, because that is the only place
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you can safely delete variables without messing up ctf_rollback. */
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/* Delete symbols that have been assigned names from the variable section. Must
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be called from within ctf_serialize, because that is the only place you can
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safely delete variables without messing up ctf_rollback. */
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static int
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symtypetab_delete_nonstatic_vars (ctf_dict_t *fp, ctf_dict_t *symfp)
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symtypetab_delete_nonstatics (ctf_dict_t *fp, ctf_dict_t *symfp)
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{
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ctf_dvdef_t *dvd, *nvd;
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ctf_id_t type;
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@ -445,8 +445,10 @@ symtypetab_delete_nonstatic_vars (ctf_dict_t *fp, ctf_dict_t *symfp)
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{
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nvd = ctf_list_next (dvd);
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if (((type = (ctf_id_t) (uintptr_t)
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ctf_dynhash_lookup (fp->ctf_objthash, dvd->dvd_name)) > 0)
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if ((((type = (ctf_id_t) (uintptr_t)
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ctf_dynhash_lookup (fp->ctf_objthash, dvd->dvd_name)) > 0)
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|| (type = (ctf_id_t) (uintptr_t)
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ctf_dynhash_lookup (fp->ctf_funchash, dvd->dvd_name)) > 0)
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&& ctf_dynhash_lookup (symfp->ctf_dynsyms, dvd->dvd_name) != NULL
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&& type == dvd->dvd_type)
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ctf_dvd_delete (fp, dvd);
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@ -560,13 +562,12 @@ ctf_symtypetab_sect_sizes (ctf_dict_t *fp, emit_symtypetab_state_t *s,
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/* If we are filtering symbols out, those symbols that the linker has not
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reported have now been removed from the ctf_objthash and ctf_funchash.
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Delete entries from the variable section that duplicate newly-added data
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symbols. There's no need to migrate new ones in, because the compiler
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always emits both a variable and a data symbol simultaneously, and
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filtering only happens at final link time. */
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Delete entries from the variable section that duplicate newly-added
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symbols. There's no need to migrate new ones in: we do that (if necessary)
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in ctf_link_deduplicating_variables. */
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if (s->filter_syms && s->symfp->ctf_dynsyms &&
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symtypetab_delete_nonstatic_vars (fp, s->symfp) < 0)
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symtypetab_delete_nonstatics (fp, s->symfp) < 0)
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return -1;
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return 0;
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