Re: [PATCH v2 6/6] bpf,btf: enable BTF pruning by default for BPF
On 5/2/24 10:11, David Faust wrote:
This patch enables -fprune-btf by default in the BPF backend when
generating BTF information, and fixes BPF CO-RE generation when using
-fprune-btf.
When generating BPF CO-RE information, we must ensure that types used
in CO-RE relocations always have sufficient BTF information emited so
that the CO-RE relocations can be processed by a BPF loader. The BTF
pruning algorithm on its own does not have sufficient information to
determine which types are used in a BPF CO-RE relocation, so this
information must be supplied by the BPF backend, using a new
btf_mark_type_used function.
Co-authored-by: Cupertino Miranda
gcc/
* btfout.cc (btf_mark_type_used): New.
* ctfc.h (btf_mark_type_used): Declare it here.
* config/bpf/bpf.cc (bpf_option_override): Enable -fprune-btf
by default if -gbtf is enabled.
* config/bpf/bcore-builtins.cc (extra_fn): New typedef.
(compute_field_expr): Add callback parameter, and call it if supplied.
Fix computation for MEM_REF.
(mark_component_type_as_used): New.
(bpf_mark_types_as_used): Likewise.
(bpf_expand_core_builtin): Call here.
* doc/invoke.texi (Debugging Options): Note that -fprune-btf is
enabled by default for BPF target when generating BTF.
gcc/testsuite/
* gcc.dg/debug/btf/btf-variables-5.c: Add -fno-prune-btf to dg-options.
---
gcc/btfout.cc | 22 ++
gcc/config/bpf/bpf.cc | 5 ++
gcc/config/bpf/core-builtins.cc | 70 +--
gcc/ctfc.h| 1 +
gcc/doc/invoke.texi | 3 +
.../gcc.dg/debug/btf/btf-variables-5.c| 2 +-
6 files changed, 96 insertions(+), 7 deletions(-)
diff --git a/gcc/btfout.cc b/gcc/btfout.cc
index 93d56492bbe..da2c9d35be9 100644
--- a/gcc/btfout.cc
+++ b/gcc/btfout.cc
@@ -1539,6 +1539,28 @@ btf_late_assign_datasec_ids (ctf_container_ref ctfc)
}
}
+
+/* Manually mark that type T is used to ensure it will not be pruned.
+ Used by the BPF backend when generating BPF CO-RE to mark types used
+ in CO-RE relocations. */
+
+void
+btf_mark_type_used (tree t)
+{
+ /* If we are not going to prune anyway, this is a no-op. */
+ if (!flag_prune_btf)
+return;
+
+ gcc_assert (TYPE_P (t));
+ ctf_container_ref ctfc = ctf_get_tu_ctfc ();
+ ctf_dtdef_ref dtd = ctf_lookup_tree_type (ctfc, t);
+
+ if (!dtd)
+return;
+
+ btf_minimal_add_type (ctfc, dtd, false, false);
+}
+
/* Callback used for assembling the only-used-types list. Note that this is
the same as btf_type_list_cb above, but the hash_set traverse requires a
different function signature. */
diff --git a/gcc/config/bpf/bpf.cc b/gcc/config/bpf/bpf.cc
index e6ea211a2c6..75303ce8f46 100644
--- a/gcc/config/bpf/bpf.cc
+++ b/gcc/config/bpf/bpf.cc
@@ -221,6 +221,11 @@ bpf_option_override (void)
&& !(target_flags_explicit & MASK_BPF_CORE))
target_flags |= MASK_BPF_CORE;
+ /* -gbtf implies -fprune-btf for BPF target. */
+ if (btf_debuginfo_p ())
+SET_OPTION_IF_UNSET (_options, _options_set,
+flag_prune_btf, true);
+
/* Determine available features from ISA setting (-mcpu=). */
if (bpf_has_jmpext == -1)
bpf_has_jmpext = (bpf_isa >= ISA_V2);
diff --git a/gcc/config/bpf/core-builtins.cc b/gcc/config/bpf/core-builtins.cc
index d5a7de825ad..1b91b1c0d25 100644
--- a/gcc/config/bpf/core-builtins.cc
+++ b/gcc/config/bpf/core-builtins.cc
@@ -624,13 +624,20 @@ bpf_core_get_index (const tree node, bool *valid)
ALLOW_ENTRY_CAST is an input arguments and specifies if the function should
consider as valid expressions in which NODE entry is a cast expression (or
- tree code nop_expr). */
+ tree code nop_expr).
+
+ EXTRA_FN is a callback function to allow extra functionality with this
+ function traversal. Currently used for marking used type during expand
+ pass. */
+
+typedef void (*extra_fn) (tree);
static unsigned char
compute_field_expr (tree node, unsigned int *accessors,
bool *valid,
tree *access_node,
- bool allow_entry_cast = true)
+ bool allow_entry_cast = true,
+ extra_fn callback = NULL)
{
unsigned char n = 0;
unsigned int fake_accessors[MAX_NR_ACCESSORS];
@@ -647,6 +654,9 @@ compute_field_expr (tree node, unsigned int *accessors,
*access_node = node;
+ if (callback != NULL)
+callback (node);
+
switch (TREE_CODE (node))
{
case INDIRECT_REF:
@@ -664,17 +674,19 @@ compute_field_expr (tree node, unsigned int *accessors,
case COMPONENT_REF:
n = compute_field_expr (TREE_OPERAND (node, 0), accessors,
valid,
- access_node, false);
+ access_node, false,
[PATCH v2 6/6] bpf,btf: enable BTF pruning by default for BPF
This patch enables -fprune-btf by default in the BPF backend when
generating BTF information, and fixes BPF CO-RE generation when using
-fprune-btf.
When generating BPF CO-RE information, we must ensure that types used
in CO-RE relocations always have sufficient BTF information emited so
that the CO-RE relocations can be processed by a BPF loader. The BTF
pruning algorithm on its own does not have sufficient information to
determine which types are used in a BPF CO-RE relocation, so this
information must be supplied by the BPF backend, using a new
btf_mark_type_used function.
Co-authored-by: Cupertino Miranda
gcc/
* btfout.cc (btf_mark_type_used): New.
* ctfc.h (btf_mark_type_used): Declare it here.
* config/bpf/bpf.cc (bpf_option_override): Enable -fprune-btf
by default if -gbtf is enabled.
* config/bpf/bcore-builtins.cc (extra_fn): New typedef.
(compute_field_expr): Add callback parameter, and call it if supplied.
Fix computation for MEM_REF.
(mark_component_type_as_used): New.
(bpf_mark_types_as_used): Likewise.
(bpf_expand_core_builtin): Call here.
* doc/invoke.texi (Debugging Options): Note that -fprune-btf is
enabled by default for BPF target when generating BTF.
gcc/testsuite/
* gcc.dg/debug/btf/btf-variables-5.c: Add -fno-prune-btf to dg-options.
---
gcc/btfout.cc | 22 ++
gcc/config/bpf/bpf.cc | 5 ++
gcc/config/bpf/core-builtins.cc | 70 +--
gcc/ctfc.h| 1 +
gcc/doc/invoke.texi | 3 +
.../gcc.dg/debug/btf/btf-variables-5.c| 2 +-
6 files changed, 96 insertions(+), 7 deletions(-)
diff --git a/gcc/btfout.cc b/gcc/btfout.cc
index 93d56492bbe..da2c9d35be9 100644
--- a/gcc/btfout.cc
+++ b/gcc/btfout.cc
@@ -1539,6 +1539,28 @@ btf_late_assign_datasec_ids (ctf_container_ref ctfc)
}
}
+
+/* Manually mark that type T is used to ensure it will not be pruned.
+ Used by the BPF backend when generating BPF CO-RE to mark types used
+ in CO-RE relocations. */
+
+void
+btf_mark_type_used (tree t)
+{
+ /* If we are not going to prune anyway, this is a no-op. */
+ if (!flag_prune_btf)
+return;
+
+ gcc_assert (TYPE_P (t));
+ ctf_container_ref ctfc = ctf_get_tu_ctfc ();
+ ctf_dtdef_ref dtd = ctf_lookup_tree_type (ctfc, t);
+
+ if (!dtd)
+return;
+
+ btf_minimal_add_type (ctfc, dtd, false, false);
+}
+
/* Callback used for assembling the only-used-types list. Note that this is
the same as btf_type_list_cb above, but the hash_set traverse requires a
different function signature. */
diff --git a/gcc/config/bpf/bpf.cc b/gcc/config/bpf/bpf.cc
index e6ea211a2c6..75303ce8f46 100644
--- a/gcc/config/bpf/bpf.cc
+++ b/gcc/config/bpf/bpf.cc
@@ -221,6 +221,11 @@ bpf_option_override (void)
&& !(target_flags_explicit & MASK_BPF_CORE))
target_flags |= MASK_BPF_CORE;
+ /* -gbtf implies -fprune-btf for BPF target. */
+ if (btf_debuginfo_p ())
+SET_OPTION_IF_UNSET (_options, _options_set,
+flag_prune_btf, true);
+
/* Determine available features from ISA setting (-mcpu=). */
if (bpf_has_jmpext == -1)
bpf_has_jmpext = (bpf_isa >= ISA_V2);
diff --git a/gcc/config/bpf/core-builtins.cc b/gcc/config/bpf/core-builtins.cc
index d5a7de825ad..1b91b1c0d25 100644
--- a/gcc/config/bpf/core-builtins.cc
+++ b/gcc/config/bpf/core-builtins.cc
@@ -624,13 +624,20 @@ bpf_core_get_index (const tree node, bool *valid)
ALLOW_ENTRY_CAST is an input arguments and specifies if the function should
consider as valid expressions in which NODE entry is a cast expression (or
- tree code nop_expr). */
+ tree code nop_expr).
+
+ EXTRA_FN is a callback function to allow extra functionality with this
+ function traversal. Currently used for marking used type during expand
+ pass. */
+
+typedef void (*extra_fn) (tree);
static unsigned char
compute_field_expr (tree node, unsigned int *accessors,
bool *valid,
tree *access_node,
- bool allow_entry_cast = true)
+ bool allow_entry_cast = true,
+ extra_fn callback = NULL)
{
unsigned char n = 0;
unsigned int fake_accessors[MAX_NR_ACCESSORS];
@@ -647,6 +654,9 @@ compute_field_expr (tree node, unsigned int *accessors,
*access_node = node;
+ if (callback != NULL)
+callback (node);
+
switch (TREE_CODE (node))
{
case INDIRECT_REF:
@@ -664,17 +674,19 @@ compute_field_expr (tree node, unsigned int *accessors,
case COMPONENT_REF:
n = compute_field_expr (TREE_OPERAND (node, 0), accessors,
valid,
- access_node, false);
+ access_node, false, callback);
accessors[n] = bpf_core_get_index (TREE_OPERAND (node, 1), valid);
