BPF programs are not typically linked, which means we cannot fall back
on library calls to implement __builtin_{memmove,memcpy} and should
always expand them inline if possible.
GCC already successfully expands these builtins inline in many cases,
but failed to do so for a few for simple cases involving overlapping
memmove in the kernel BPF selftests and was instead emitting a libcall.
This patch implments a simple inline expansion of memcpy and memmove in
the BPF backend in a verifier-friendly way, with the caveat that the
size must be an integer constant, which is also required by clang.
Tested for bpf-unknown-none on x86_64-linux-gnu host.
Also tested against the BPF verifier by compiling and loading a test
program with overlapping memmove (essentially the memmove-1.c test)
which failed before due to a libcall, and now successfully loads and
passes the verifier.
gcc/
* config/bpf/bpf-protos.h (bpf_expand_cpymem): New.
* config/bpf/bpf.cc: (emit_move_loop, CPYMEM_EXPAND_ERR)
(bpf_expand_cpymem): New.
* config/bpf/bpf.md: (cpymemdi, movmemdi): New define_expands.
gcc/testsuite/
* gcc.target/bpf/memcpy-1.c: New test.
* gcc.target/bpf/memmove-1.c: New test.
* gcc.target/bpf/memmove-2.c: New test.
---
gcc/config/bpf/bpf-protos.h | 2 +
gcc/config/bpf/bpf.cc | 129 +++++++++++++++++++++++
gcc/config/bpf/bpf.md | 36 +++++++
gcc/testsuite/gcc.target/bpf/memcpy-1.c | 26 +++++
gcc/testsuite/gcc.target/bpf/memmove-1.c | 46 ++++++++
gcc/testsuite/gcc.target/bpf/memmove-2.c | 23 ++++
6 files changed, 262 insertions(+)
create mode 100644 gcc/testsuite/gcc.target/bpf/memcpy-1.c
create mode 100644 gcc/testsuite/gcc.target/bpf/memmove-1.c
create mode 100644 gcc/testsuite/gcc.target/bpf/memmove-2.c
diff --git a/gcc/config/bpf/bpf-protos.h b/gcc/config/bpf/bpf-protos.h
index 46d950bd990..366acb87ae4 100644
--- a/gcc/config/bpf/bpf-protos.h
+++ b/gcc/config/bpf/bpf-protos.h
@@ -35,4 +35,6 @@ const char *bpf_add_core_reloc (rtx *operands, const char
*templ);
class gimple_opt_pass;
gimple_opt_pass *make_pass_lower_bpf_core (gcc::context *ctxt);
+bool bpf_expand_cpymem (rtx *, bool);
+
#endif /* ! GCC_BPF_PROTOS_H */
diff --git a/gcc/config/bpf/bpf.cc b/gcc/config/bpf/bpf.cc
index d6ca47eeecb..c90d29d12ff 100644
--- a/gcc/config/bpf/bpf.cc
+++ b/gcc/config/bpf/bpf.cc
@@ -1184,6 +1184,135 @@ bpf_use_by_pieces_infrastructure_p (unsigned
HOST_WIDE_INT size,
#define TARGET_USE_BY_PIECES_INFRASTRUCTURE_P \
bpf_use_by_pieces_infrastructure_p
+/* Helper for bpf_expand_cpymem. Emit an unrolled loop moving the bytes
+ from SRC to DST. */
+
+static void
+emit_move_loop (rtx src, rtx dst, machine_mode mode, int offset, int inc,
+ unsigned iters, unsigned remainder)
+{
+ rtx reg = gen_reg_rtx (mode);
+
+ /* First copy in chunks as large as alignment permits. */
+ for (unsigned int i = 0; i < iters; i++)
+ {
+ emit_move_insn (reg, adjust_address (src, mode, offset));
+ emit_move_insn (adjust_address (dst, mode, offset), reg);
+ offset += inc;
+ }
+
+ /* Handle remaining bytes which might be smaller than the chunks
+ used above. */
+ if (remainder & 4)
+ {
+ emit_move_insn (reg, adjust_address (src, SImode, offset));
+ emit_move_insn (adjust_address (dst, SImode, offset), reg);
+ offset += (inc < 0 ? -4 : 4);
+ remainder -= 4;
+ }
+ if (remainder & 2)
+ {
+ emit_move_insn (reg, adjust_address (src, HImode, offset));
+ emit_move_insn (adjust_address (dst, HImode, offset), reg);
+ offset += (inc < 0 ? -2 : 2);
+ remainder -= 2;
+ }
+ if (remainder & 1)
+ {
+ emit_move_insn (reg, adjust_address (src, QImode, offset));
+ emit_move_insn (adjust_address (dst, QImode, offset), reg);
+ }
+}
+
+/* Error if we cannot completely expand the memcpy/memmove inline,
+ unless we are building libgcc. */
+#define CPYMEM_EXPAND_ERR(LOC, MSG) \
+ do \
+ { \
+ if (flag_building_libgcc)
\
+ warning (LOC, MSG " for BPF memcpy/memmove expansion; " \
+ "a libcall will be emitted"); \
+ else \
+ error (MSG " for BPF memcpy/memmove expansion"); \
+ } while (0);
+
+/* Expand cpymem/movmem, as from __builtin_memcpy/memmove.
+ OPERANDS are the same as the cpymem/movmem patterns.
+ IS_MOVE is true if this is a memmove, false for memcpy.
+ Return true if we successfully expanded, or false if we cannot
+ and must punt to a libcall. */
+
+bool
+bpf_expand_cpymem (rtx *operands, bool is_move)
+{
+ /* Size and alignment must be constant. */
+ if (!CONST_INT_P (operands[2]))
+ {
+ CPYMEM_EXPAND_ERR (RTL_LOCATION (operands[2]),
+ "unsupported variable size");
+ return false;
+ }
+ if (!CONST_INT_P (operands[3]))
+ {
+ CPYMEM_EXPAND_ERR (RTL_LOCATION (operands[3]),
+ "unsupported variable alignment");
+ return false;
+ }
+
+ rtx dst = operands[0];
+ rtx src = operands[1];
+ rtx size = operands[2];
+ unsigned HOST_WIDE_INT size_bytes = UINTVAL (size);
+ unsigned align = UINTVAL (operands[3]);
+ enum machine_mode mode;
+ switch (align)
+ {
+ case 1: mode = QImode; break;
+ case 2: mode = HImode; break;
+ case 4: mode = SImode; break;
+ case 8: mode = DImode; break;
+ default:
+ CPYMEM_EXPAND_ERR (RTL_LOCATION (operands[3]),
+ "unsupported alignment");
+ return false;
+ }
+
+ unsigned iters = size_bytes >> ceil_log2 (align);
+ unsigned remainder = size_bytes & (align - 1);
+
+ int inc = GET_MODE_SIZE (mode);
+ rtx_code_label *fwd_label, *done_label;
+ if (is_move)
+ {
+ /* For memmove, be careful of overlap. It is not a concern for memcpy.
+ To handle overlap, we check (at runtime) if SRC < DST, and if so do
+ the move "backwards" starting from SRC + SIZE. */
+ fwd_label = gen_label_rtx ();
+ done_label = gen_label_rtx ();
+
+ rtx dst_addr = copy_to_mode_reg (Pmode, XEXP (dst, 0));
+ rtx src_addr = copy_to_mode_reg (Pmode, XEXP (src, 0));
+ emit_cmp_and_jump_insns (src_addr, dst_addr, GEU, NULL_RTX, Pmode,
+ true, fwd_label, profile_probability::even ());
+
+ /* Emit the "backwards" unrolled loop. */
+ emit_move_loop (src, dst, mode, size_bytes, -inc, iters, remainder);
+ emit_jump_insn (gen_jump (done_label));
+ emit_barrier ();
+
+ emit_label (fwd_label);
+ }
+
+ emit_move_loop (src, dst, mode, 0, inc, iters, remainder);
+
+ if (is_move)
+ emit_label (done_label);
+
+ return true;
+}
+
+#undef CPYMEM_EXPAND_ERR
+
/* Finally, build the GCC target. */
struct gcc_target targetm = TARGET_INITIALIZER;
diff --git a/gcc/config/bpf/bpf.md b/gcc/config/bpf/bpf.md
index 50df1aaa3e2..ca677bc6b50 100644
--- a/gcc/config/bpf/bpf.md
+++ b/gcc/config/bpf/bpf.md
@@ -627,4 +627,40 @@ (define_insn "ldabs<ldop>"
"{ldabs<ldop>\t%0|r0 = *(<pldop> *) skb[%0]}"
[(set_attr "type" "ld")])
+;;; memmove and memcopy
+
+;; 0 is dst
+;; 1 is src
+;; 2 is size of copy in bytes
+;; 3 is alignment
+
+(define_expand "cpymemdi"
+ [(match_operand:BLK 0 "memory_operand")
+ (match_operand:BLK 1 "memory_operand")
+ (match_operand:DI 2 "general_operand")
+ (match_operand:DI 3 "immediate_operand")]
+ ""
+{
+ if (bpf_expand_cpymem (operands, false))
+ DONE;
+ FAIL;
+})
+
+;; 0 is dst
+;; 1 is src
+;; 2 is size of copy in bytes
+;; 3 is alignment
+
+(define_expand "movmemdi"
+ [(match_operand:BLK 0 "memory_operand")
+ (match_operand:BLK 1 "memory_operand")
+ (match_operand:DI 2 "general_operand")
+ (match_operand:DI 3 "immediate_operand")]
+ ""
+{
+ if (bpf_expand_cpymem (operands, true))
+ DONE;
+ FAIL;
+})
+
(include "atomic.md")
diff --git a/gcc/testsuite/gcc.target/bpf/memcpy-1.c
b/gcc/testsuite/gcc.target/bpf/memcpy-1.c
new file mode 100644
index 00000000000..6c9707f24e8
--- /dev/null
+++ b/gcc/testsuite/gcc.target/bpf/memcpy-1.c
@@ -0,0 +1,26 @@
+/* Ensure memcpy is expanded inline rather than emitting a libcall. */
+
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+
+struct context {
+ unsigned int data;
+ unsigned int data_end;
+ unsigned int data_meta;
+ unsigned int ingress;
+ unsigned int queue_index;
+ unsigned int egress;
+};
+
+void
+cpy_1(struct context *ctx)
+{
+ void *data = (void *)(long)ctx->data;
+ char *dest;
+ dest = data;
+ dest += 16;
+
+ __builtin_memcpy (dest, data, 8);
+}
+
+/* { dg-final { scan-assembler-times "call" 0 } } */
diff --git a/gcc/testsuite/gcc.target/bpf/memmove-1.c
b/gcc/testsuite/gcc.target/bpf/memmove-1.c
new file mode 100644
index 00000000000..3b8ba82639e
--- /dev/null
+++ b/gcc/testsuite/gcc.target/bpf/memmove-1.c
@@ -0,0 +1,46 @@
+/* Ensure memmove is expanded inline rather than emitting a libcall. */
+
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+
+struct context {
+ unsigned int data;
+ unsigned int data_end;
+ unsigned int data_meta;
+ unsigned int ingress;
+ unsigned int queue_index;
+ unsigned int egress;
+};
+
+void
+mov_1_nooverlap (struct context *ctx)
+{
+ void *data = (void *)(long)ctx->data;
+ char *dest;
+ dest = data;
+ dest += 16;
+
+ __builtin_memmove (dest, data, 12);
+}
+
+void
+mov_1_overlap (struct context *ctx)
+{
+ void *data = (void *)(long)ctx->data;
+ char *dest;
+ dest = data;
+ dest += 4;
+
+ __builtin_memmove (dest, data, 12);
+}
+
+void
+mov_1_arbitrary (struct context *ctx_a, struct context *ctx_b)
+{
+ void *src = (void *)(long)ctx_a->data;
+ void *dst = (void *)(long)ctx_b->data;
+
+ __builtin_memmove (dst, src, 12);
+}
+
+/* { dg-final { scan-assembler-times "call" 0 } } */
diff --git a/gcc/testsuite/gcc.target/bpf/memmove-2.c
b/gcc/testsuite/gcc.target/bpf/memmove-2.c
new file mode 100644
index 00000000000..0ef34131080
--- /dev/null
+++ b/gcc/testsuite/gcc.target/bpf/memmove-2.c
@@ -0,0 +1,23 @@
+/* Test that we error if memmove cannot be expanded inline. */
+
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+
+typedef unsigned int __u32;
+
+struct context {
+ unsigned int data;
+ unsigned int data_end;
+ unsigned int data_meta;
+};
+
+void
+mov_2_unsupported (struct context *ctx)
+{
+ void *data = (void *)(long)ctx->data;
+ char *dest;
+ dest = data;
+ dest += 4;
+
+ __builtin_memmove (dest, data, ctx->data_meta); /* { dg-error "unsupported
variable size" } */
+}
--
2.43.0
