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From: David Faust <dfaust@gcc.gnu.org> To: gcc-cvs@gcc.gnu.org Subject: [gcc r13-4707] btf: add 'extern' linkage for variables [PR106773] Date: Wed, 14 Dec 2022 18:25:51 +0000 (GMT) [thread overview] Message-ID: <20221214182551.88E60382BE99@sourceware.org> (raw) https://gcc.gnu.org/g:2bce22e88e1c8486a0f2d42311506a8d3da20fb7 commit r13-4707-g2bce22e88e1c8486a0f2d42311506a8d3da20fb7 Author: David Faust <david.faust@oracle.com> Date: Wed Dec 7 11:44:28 2022 -0800 btf: add 'extern' linkage for variables [PR106773] Add support for the 'extern' linkage value for BTF_KIND_VAR records, which is used for variables declared as extern in the source file. This also fixes a bug with BTF generation for extern variables which have both a non-defining declaration and a defining declaration in the same CU. PR target/106773 gcc/ * btfout.cc (btf_collect_datasec): Mark extern variables as such. (btf_dvd_emit_preprocess_cb): Skip non-defining extern variable decl if there is a defining decl for the same variable. (btf_asm_varent): Accomodate 'extern' linkage. gcc/testsuite/ * gcc.dg/debug/btf/btf-variables-4.c: New test. * gcc.dg/debug/btf/btf-variables-5.c: New test. include/ * btf.h (enum btf_var_linkage): New. (struct btf_var): Update comment to note 'extern' linkage. Diff: --- gcc/btfout.cc | 11 ++++++++++- gcc/testsuite/gcc.dg/debug/btf/btf-variables-4.c | 24 ++++++++++++++++++++++++ gcc/testsuite/gcc.dg/debug/btf/btf-variables-5.c | 19 +++++++++++++++++++ include/btf.h | 11 ++++++++++- 4 files changed, 63 insertions(+), 2 deletions(-) diff --git a/gcc/btfout.cc b/gcc/btfout.cc index aef9fd70a28..677e8324424 100644 --- a/gcc/btfout.cc +++ b/gcc/btfout.cc @@ -314,6 +314,9 @@ btf_collect_datasec (ctf_container_ref ctfc) continue; const char *section_name = node->get_section (); + /* Mark extern variables. */ + if (DECL_EXTERNAL (node->decl)) + dvd->dvd_visibility = BTF_VAR_GLOBAL_EXTERN; if (section_name == NULL) { @@ -431,6 +434,12 @@ btf_dvd_emit_preprocess_cb (ctf_dvdef_ref *slot, ctf_container_ref arg_ctfc) { ctf_dvdef_ref var = (ctf_dvdef_ref) * slot; + /* If this is an extern variable declaration with a defining declaration + later, skip it so that only the defining declaration is emitted. + This is the same case, fix and reasoning as in CTF; see PR105089. */ + if (ctf_dvd_ignore_lookup (arg_ctfc, var->dvd_key)) + return 1; + /* Do not add variables which refer to unsupported types. */ if (btf_removed_type_p (var->dvd_type)) return 1; @@ -676,7 +685,7 @@ btf_asm_varent (ctf_dvdef_ref var) dw2_asm_output_data (4, var->dvd_name_offset, "btv_name"); dw2_asm_output_data (4, BTF_TYPE_INFO (BTF_KIND_VAR, 0, 0), "btv_info"); dw2_asm_output_data (4, get_btf_id (var->dvd_type), "btv_type"); - dw2_asm_output_data (4, (var->dvd_visibility ? 1 : 0), "btv_linkage"); + dw2_asm_output_data (4, var->dvd_visibility, "btv_linkage"); } /* Asm'out a member description following a BTF_KIND_STRUCT or diff --git a/gcc/testsuite/gcc.dg/debug/btf/btf-variables-4.c b/gcc/testsuite/gcc.dg/debug/btf/btf-variables-4.c new file mode 100644 index 00000000000..d77600bae1c --- /dev/null +++ b/gcc/testsuite/gcc.dg/debug/btf/btf-variables-4.c @@ -0,0 +1,24 @@ +/* Test BTF generation for extern variables. */ + +/* { dg-do compile } */ +/* { dg-options "-O0 -gbtf -dA" } */ + +/* Expect 4 variables. */ +/* { dg-final { scan-assembler-times "\[\t \]0xe000000\[\t \]+\[^\n\]*btv_info" 4 } } */ + +/* 2 extern, 1 global, 1 static. */ +/* { dg-final { scan-assembler-times "\[\t \]0\[\t \]+\[^\n\]*btv_linkage" 1 } } */ +/* { dg-final { scan-assembler-times "\[\t \]0x1\[\t \]+\[^\n\]*btv_linkage" 1 } } */ +/* { dg-final { scan-assembler-times "\[\t \]0x2\[\t \]+\[^\n\]*btv_linkage" 2 } } */ + +extern int a; +extern const int b; +int c; +static const int d = 5; + +int foo (int x) +{ + c = a + b + x; + + return c + d; +} diff --git a/gcc/testsuite/gcc.dg/debug/btf/btf-variables-5.c b/gcc/testsuite/gcc.dg/debug/btf/btf-variables-5.c new file mode 100644 index 00000000000..8aae76cacab --- /dev/null +++ b/gcc/testsuite/gcc.dg/debug/btf/btf-variables-5.c @@ -0,0 +1,19 @@ +/* Test BTF generation for extern variable with both non-defining and + defining declarations. + + In this case, only a single variable record should be emitted, + with 'global' linkage. However two array types will be generated. */ + +/* { dg-do compile } */ +/* { dg-options "-O0 -gbtf -dA" } */ + +/* Expect 1 variable with global (1) linkage. */ +/* { dg-final { scan-assembler-times "\[\t \]0xe000000\[\t \]+\[^\n\]*btv_info" 1 } } */ +/* { dg-final { scan-assembler-times "\[\t \]0x1\[\t \]+\[^\n\]*btv_linkage" 1 } } */ + +/* Expect 2 array types, one of which is unsized. */ +/* { dg-final { scan-assembler-times "\[\t \]0x4\[\t \]+\[^\n\]*bta_nelems" 1 } } */ +/* { dg-final { scan-assembler-times "\[\t \]0\[\t \]+\[^\n\]*bta_nelems" 1 } } */ + +extern const char FOO[]; +const char FOO[] = "foo"; diff --git a/include/btf.h b/include/btf.h index eba67f9d599..da621353aa1 100644 --- a/include/btf.h +++ b/include/btf.h @@ -178,11 +178,20 @@ struct btf_param uint32_t type; /* Type of parameter. */ }; +/* BTF_KIND_VAR records encode linkage information in a single + trailing struct btf_var. These are the supported values. */ +enum btf_var_linkage +{ + BTF_VAR_STATIC = 0, + BTF_VAR_GLOBAL_ALLOCATED = 1, + BTF_VAR_GLOBAL_EXTERN = 2, +}; + /* BTF_KIND_VAR is followed by a single struct btf_var, which describes information about the variable. */ struct btf_var { - uint32_t linkage; /* Currently only 0=static or 1=global. */ + uint32_t linkage; /* 0=static, 1=global, 2=extern. */ }; /* BTF_KIND_DATASEC is followed by VLEN struct btf_var_secinfo entries,
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