[PATCH V6 1/3] gdb: support for eBPF

Jose E. Marchesi
2020-08-03T14:02:47Z

This patch adds basic support for the eBPF target: tdep and build
machinery. The accompanying simulator is introduced in subsequent
patches.

gdb/ChangeLog:

2020-08-03 Weimin Pan <weimin.pan@oracle.com>
Jose E. Marchesi <jose.marchesi@oracle.com>

* configure.tgt: Add entry for bpf-*-*.
* Makefile.in (ALL_TARGET_OBS): Add bpf-tdep.o
(ALLDEPFILES): Add bpf-tdep.c.
* bpf-tdep.c: New file.
* MAINTAINERS: Add bpf target and maintainer.

gdb/doc/ChangeLog:

2020-08-03 Jose E. Marchesi <jose.marchesi@oracle.com>

* gdb.texinfo (Contributors): Add information for the eBPF
support.
(BPF): New section.
---
gdb/ChangeLog | 9 ++
gdb/MAINTAINERS | 3 +
gdb/Makefile.in | 2 +
gdb/bpf-tdep.c | 387 ++++++++++++++++++++++++++++++++++++++++++++
gdb/configure.tgt | 5 +
gdb/doc/ChangeLog | 6 +
gdb/doc/gdb.texinfo | 21 +++
7 files changed, 433 insertions(+)
create mode 100644 gdb/bpf-tdep.c

diff --git a/gdb/MAINTAINERS b/gdb/MAINTAINERS
index b6c31f6a60..9dd6f65b5c 100644
--- a/gdb/MAINTAINERS
+++ b/gdb/MAINTAINERS
@@ -247,6 +247,9 @@ the native maintainer when resolving ABI issues.

avr --target=avr ,-Werror

+ bpf --target=bpf-unknown-none
+ Jose E. Marchesi jose.marchesi@oracle.com
+
cris --target=cris-elf ,-Werror ,
(sim does not build with -Werror)

diff --git a/gdb/Makefile.in b/gdb/Makefile.in
index 0d6d8137b5..67dc9daf16 100644
--- a/gdb/Makefile.in
+++ b/gdb/Makefile.in
@@ -719,6 +719,7 @@ ALL_TARGET_OBS = \
avr-tdep.o \
bfin-linux-tdep.o \
bfin-tdep.o \
+ bpf-tdep.o \
bsd-uthread.o \
cris-linux-tdep.o \
cris-tdep.o \
@@ -2147,6 +2148,7 @@ ALLDEPFILES = \
avr-tdep.c \
bfin-linux-tdep.c \
bfin-tdep.c \
+ bpf-tdep.c \
bsd-kvm.c \
bsd-uthread.c \
csky-linux-tdep.c \
diff --git a/gdb/bpf-tdep.c b/gdb/bpf-tdep.c
new file mode 100644
index 0000000000..204cb01e70
--- /dev/null
+++ b/gdb/bpf-tdep.c
@@ -0,0 +1,387 @@
+/* Target-dependent code for BPF.
+
+ Copyright (C) 2020 Free Software Foundation, Inc.
+
+ This file is part of GDB.
+
+ This program is free software; you can redistribute it and/or modify
+ it under the terms of the GNU General Public License as published by
+ the Free Software Foundation; either version 3 of the License, or
+ (at your option) any later version.
+
+ This program is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with this program. If not, see <http://www.gnu.org/licenses/>. */
+
+#include "defs.h"
+#include "arch-utils.h"
+#include "dis-asm.h"
+#include "frame.h"
+#include "frame-unwind.h"
+#include "trad-frame.h"
+#include "symtab.h"
+#include "value.h"
+#include "gdbcmd.h"
+#include "breakpoint.h"
+#include "inferior.h"
+#include "regcache.h"
+#include "target.h"
+#include "dwarf2/frame.h"
+#include "osabi.h"
+#include "target-descriptions.h"
+#include "remote.h"
+
+\f
+/* eBPF registers. */
+
+enum bpf_regnum
+{
+ BPF_R0_REGNUM, /* return value */
+ BPF_R1_REGNUM,
+ BPF_R2_REGNUM,
+ BPF_R3_REGNUM,
+ BPF_R4_REGNUM,
+ BPF_R5_REGNUM,
+ BPF_R6_REGNUM,
+ BPF_R7_REGNUM,
+ BPF_R8_REGNUM,
+ BPF_R9_REGNUM,
+ BPF_R10_REGNUM, /* sp */
+ BPF_PC_REGNUM,
+};
+
+#define BPF_NUM_REGS (BPF_PC_REGNUM + 1)
+
+/* Target-dependent structure in gdbarch. */
+struct gdbarch_tdep
+{
+};
+
+\f
+/* Internal debugging facilities. */
+
+/* When this is set to non-zero debugging information will be
+ printed. */
+
+static unsigned int bpf_debug_flag = 0;
+
+/* The show callback for 'show debug bpf'. */
+
+static void
+show_bpf_debug (struct ui_file *file, int from_tty,
+ struct cmd_list_element *c, const char *value)
+{
+ fprintf_filtered (file, _("Debugging of BPF is %s.\n"), value);
+}
+
+\f
+/* BPF registers */
+
+static const char *bpf_register_names[] =
+{
+ "r0", "r1", "r2", "r3", "r4", "r5", "r6", "r7",
+ "r8", "r9", "r10", "pc"
+};
+
+/* Return the name of register REGNUM. */
+
+static const char *
+bpf_register_name (struct gdbarch *gdbarch, int reg)
+{
+ if (reg >= 0 && reg < BPF_NUM_REGS)
+ return bpf_register_names[reg];
+ return NULL;
+}
+
+/* Return the GDB type of register REGNUM. */
+
+static struct type *
+bpf_register_type (struct gdbarch *gdbarch, int reg)
+{
+ if (reg == BPF_R10_REGNUM)
+ return builtin_type (gdbarch)->builtin_data_ptr;
+ else if (reg == BPF_PC_REGNUM)
+ return builtin_type (gdbarch)->builtin_func_ptr;
+ return builtin_type (gdbarch)->builtin_int64;
+}
+
+/* Return the GDB register number corresponding to DWARF's REG. */
+
+static int
+bpf_dwarf2_reg_to_regnum (struct gdbarch *gdbarch, int reg)
+{
+ if (reg >= 0 && reg < BPF_NUM_REGS)
+ return reg;
+ return -1;
+}
+
+/* Implement the "print_insn" gdbarch method. */
+
+static int
+bpf_gdb_print_insn (bfd_vma memaddr, disassemble_info *info)
+{
+ info->symbols = NULL;
+ return default_print_insn (memaddr, info);
+}
+
+\f
+/* Return PC of first real instruction of the function starting at
+ START_PC. */
+
+static CORE_ADDR
+bpf_skip_prologue (struct gdbarch *gdbarch, CORE_ADDR start_pc)
+{
+ fprintf_unfiltered (gdb_stdlog,
+ "Skipping prologue: start_pc=%s\n",
+ paddress (gdbarch, start_pc));
+ /* XXX: to be completed. */
+ return start_pc + 0;
+}
+
+\f
+/* Frame unwinder.
+
+ XXX it is not clear how to unwind in eBPF, since the stack is not
+ guaranteed to be contiguous, and therefore no relative stack
+ addressing can be done in the callee in order to access the
+ caller's stack frame. To explore with xBPF, which will relax this
+ restriction. */
+
+/* Given THIS_FRAME, return its ID. */
+
+static void
+bpf_frame_this_id (struct frame_info *this_frame,
+ void **this_prologue_cache,
+ struct frame_id *this_id)
+{
+ /* Note that THIS_ID defaults to the outermost frame if we don't set
+ anything here. See frame.c:compute_frame_id. */
+}
+
+/* Return the reason why we can't unwind past THIS_FRAME. */
+
+static enum unwind_stop_reason
+bpf_frame_unwind_stop_reason (struct frame_info *this_frame,
+ void **this_cache)
+{
+ return UNWIND_OUTERMOST;
+}
+
+/* Ask THIS_FRAME to unwind its register. */
+
+static struct value *
+bpf_frame_prev_register (struct frame_info *this_frame,
+ void **this_prologue_cache, int regnum)
+{
+ return frame_unwind_got_register (this_frame, regnum, regnum);
+}
+
+/* Frame unwinder machinery for BPF. */
+
+static const struct frame_unwind bpf_frame_unwind =
+{
+ NORMAL_FRAME,
+ bpf_frame_unwind_stop_reason,
+ bpf_frame_this_id,
+ bpf_frame_prev_register,
+ NULL,
+ default_frame_sniffer
+};
+
+\f
+/* Breakpoints. */
+
+/* Enum describing the different kinds of breakpoints. We currently
+ just support one, implemented by the brkpt xbpf instruction. */
+
+enum bpf_breakpoint_kinds
+{
+ BPF_BP_KIND_BRKPT = 0,
+};
+
+/* Implement the breakpoint_kind_from_pc gdbarch method. */
+
+static int
+bpf_breakpoint_kind_from_pc (struct gdbarch *gdbarch, CORE_ADDR *start_pc)
+{
+ /* We support just one kind of breakpoint. */
+ return BPF_BP_KIND_BRKPT;
+}
+
+/* Implement the sw_breakpoint_from_kind gdbarch method. */
+
+static const gdb_byte *
+bpf_sw_breakpoint_from_kind (struct gdbarch *gdbarch, int kind, int *size)
+{
+ static unsigned char brkpt_insn[]
+ = {0x8c, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
+
+ switch (kind)
+ {
+ case BPF_BP_KIND_BRKPT:
+ *size = 8;
+ return brkpt_insn;
+ default:
+ gdb_assert_not_reached ("unexpected BPF breakpoint kind");
+ }
+}
+
+\f
+/* Assuming THIS_FRAME is a dummy frame, return its frame ID. */
+
+static struct frame_id
+bpf_dummy_id (struct gdbarch *gdbarch, struct frame_info *this_frame)
+{
+ CORE_ADDR sp = get_frame_register_unsigned (this_frame,
+ gdbarch_sp_regnum (gdbarch));
+ return frame_id_build (sp, get_frame_pc (this_frame));
+}
+
+/* Implement the push dummy call gdbarch callback. */
+
+static CORE_ADDR
+bpf_push_dummy_call (struct gdbarch *gdbarch, struct value *function,
+ struct regcache *regcache, CORE_ADDR bp_addr,
+ int nargs, struct value **args, CORE_ADDR sp,
+ function_call_return_method return_method,
+ CORE_ADDR struct_addr)
+{
+ fprintf_unfiltered (gdb_stdlog,
+ "Pushing dummy call: sp=%s\n",
+ paddress (gdbarch, sp));
+ /* XXX writeme */
+ return sp;
+}
+
+/* Extract a function return value of TYPE from REGCACHE,
+ and copy it into VALBUF. */
+
+static void
+bpf_extract_return_value (struct type *type, struct regcache *regcache,
+ gdb_byte *valbuf)
+{
+ int len = TYPE_LENGTH (type);
+ gdb_byte vbuf[8];
+
+ gdb_assert (len <= 8);
+ regcache->cooked_read (BPF_R0_REGNUM, vbuf);
+ memcpy (valbuf, vbuf + 8 - len, len);
+}
+
+/* Store the function return value of type TYPE from VALBUF into REGNAME. */
+
+static void
+bpf_store_return_value (struct type *type, struct regcache *regcache,
+ const gdb_byte *valbuf)
+{
+ int len = TYPE_LENGTH (type);
+ gdb_byte vbuf[8];
+
+ gdb_assert (len <= 8);
+ memset (vbuf, 0, sizeof (vbuf));
+ memcpy (vbuf + 8 - len, valbuf, len);
+ regcache->cooked_write (BPF_R0_REGNUM, vbuf);
+}
+
+/* Handle function's return value. */
+
+static enum return_value_convention
+bpf_return_value (struct gdbarch *gdbarch, struct value *function,
+ struct type *type, struct regcache *regcache,
+ gdb_byte *readbuf, const gdb_byte *writebuf)
+{
+ int len = TYPE_LENGTH (type);
+
+ if (len > 8)
+ return RETURN_VALUE_STRUCT_CONVENTION;
+
+ if (readbuf != NULL)
+ bpf_extract_return_value (type, regcache, readbuf);
+ if (writebuf != NULL)
+ bpf_store_return_value (type, regcache, writebuf);
+
+ return RETURN_VALUE_REGISTER_CONVENTION;
+}
+
+\f
+/* Initialize the current architecture based on INFO. If possible, re-use an
+ architecture from ARCHES, which is a list of architectures already created
+ during this debugging session. */
+
+static struct gdbarch *
+bpf_gdbarch_init (struct gdbarch_info info, struct gdbarch_list *arches)
+{
+ /* If there is already a candidate, use it. */
+ arches = gdbarch_list_lookup_by_info (arches, &info);
+ if (arches != NULL)
+ return arches->gdbarch;
+
+ /* Allocate space for the new architecture. */
+ struct gdbarch_tdep *tdep = XCNEW (struct gdbarch_tdep);
+ struct gdbarch *gdbarch = gdbarch_alloc (&info, tdep);
+
+ /* Information about registers, etc. */
+ set_gdbarch_num_regs (gdbarch, BPF_NUM_REGS);
+ set_gdbarch_register_name (gdbarch, bpf_register_name);
+ set_gdbarch_register_type (gdbarch, bpf_register_type);
+
+ /* Register numbers of various important registers. */
+ set_gdbarch_sp_regnum (gdbarch, BPF_R10_REGNUM);
+ set_gdbarch_pc_regnum (gdbarch, BPF_PC_REGNUM);
+
+ /* Map DWARF2 registers to GDB registers. */
+ set_gdbarch_dwarf2_reg_to_regnum (gdbarch, bpf_dwarf2_reg_to_regnum);
+
+ /* Call dummy code. */
+ set_gdbarch_call_dummy_location (gdbarch, ON_STACK);
+ set_gdbarch_dummy_id (gdbarch, bpf_dummy_id);
+ set_gdbarch_push_dummy_call (gdbarch, bpf_push_dummy_call);
+
+ /* Returning results. */
+ set_gdbarch_return_value (gdbarch, bpf_return_value);
+
+ /* Advance PC across function entry code. */
+ set_gdbarch_skip_prologue (gdbarch, bpf_skip_prologue);
+
+ /* Stack grows downward. */
+ set_gdbarch_inner_than (gdbarch, core_addr_lessthan);
+
+ /* Breakpoint manipulation. */
+ set_gdbarch_breakpoint_kind_from_pc (gdbarch, bpf_breakpoint_kind_from_pc);
+ set_gdbarch_sw_breakpoint_from_kind (gdbarch, bpf_sw_breakpoint_from_kind);
+
+ /* Frame handling. */
+ set_gdbarch_frame_args_skip (gdbarch, 8);
+
+ /* Disassembly. */
+ set_gdbarch_print_insn (gdbarch, bpf_gdb_print_insn);
+
+ /* Hook in ABI-specific overrides, if they have been registered. */
+ gdbarch_init_osabi (info, gdbarch);
+
+ /* Install unwinders. */
+ frame_unwind_append_unwinder (gdbarch, &bpf_frame_unwind);
+
+ return gdbarch;
+}
+
+void _initialize_bpf_tdep ();
+void
+_initialize_bpf_tdep (void)
+{
+ register_gdbarch_init (bfd_arch_bpf, bpf_gdbarch_init);
+
+ /* Add commands 'set/show debug bpf' */
+ add_setshow_zuinteger_cmd ("bpf", class_maintenance,
+ &bpf_debug_flag,
+ _("Set BPF debugging."),
+ _("Show BPF debugging."),
+ _("Enables BPF specific debugging output."),
+ NULL,
+ &show_bpf_debug,
+ &setdebuglist, &showdebuglist);
+}
diff --git a/gdb/configure.tgt b/gdb/configure.tgt
index d66f01bb9f..7e84eff444 100644
--- a/gdb/configure.tgt
+++ b/gdb/configure.tgt
@@ -205,6 +205,11 @@ bfin-*-*)
gdb_sim=../sim/bfin/libsim.a
;;

+bpf-*-*)
+ # Target: eBPF
+ gdb_target_obs="bpf-tdep.o"
+ ;;
+
cris*)
# Target: CRIS
gdb_target_obs="cris-tdep.o cris-linux-tdep.o linux-tdep.o solib-svr4.o"
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index 1b9f76573b..1acee080b8 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -557,6 +557,10 @@ Alessandro Forin and Per Bothner. More recent ports have been the work
of Jeremy Bennett, Franck Jullien, Stefan Wallentowitz and
Stafford Horne.

+Weimin Pan, David Faust and Jose E. Marchesi contributed support for
+the Linux kernel BPF virtual architecture. This work was sponsored by
+Oracle.
+
@node Sample Session
@chapter A Sample @value{GDBN} Session

@@ -24381,6 +24385,7 @@ acceptable commands.
@menu
* ARC:: Synopsys ARC
* ARM:: ARM
+* BPF:: eBPF
* M68K:: Motorola M68K
* MicroBlaze:: Xilinx MicroBlaze
* MIPS Embedded:: MIPS Embedded
@@ -24515,6 +24520,22 @@ The default value is @code{all}.
@end table
@end table

+@node BPF
+@subsection BPF
+
+@table @code
+@item target sim @r{[}@var{simargs}@r{]} @dots{}
+The @value{GDBN} BPF simulator accepts the following optional arguments.
+
+@table @code
+@item --skb-data-offset=@var{offset}
+Tell the simulator the offset, measured in bytes, of the
+@code{skb_data} field in the kernel @code{struct sk_buff} structure.
+This offset is used by some BPF specific-purpose load/store
+instructions. Defaults to 0.
+@end table
+@end table
+
@node M68K
@subsection M68k

--
2.25.0.2.g232378479e