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* [binutils-gdb] gdb: disassembler opcode display formatting
@ 2022-10-02 13:15 Andrew Burgess
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From: Andrew Burgess @ 2022-10-02 13:15 UTC (permalink / raw)
To: gdb-cvs
https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=d4ce49b7ac077a9882d6a5e689e260300045ca88
commit d4ce49b7ac077a9882d6a5e689e260300045ca88
Author: Andrew Burgess <aburgess@redhat.com>
Date: Tue Jun 21 20:23:35 2022 +0100
gdb: disassembler opcode display formatting
This commit changes the format of 'disassemble /r' to match GNU
objdump. Specifically, GDB will now display the instruction bytes in
as 'objdump --wide --disassemble' does.
Here is an example for RISC-V before this patch:
(gdb) disassemble /r 0x0001018e,0x0001019e
Dump of assembler code from 0x1018e to 0x1019e:
0x0001018e <call_me+66>: 03 26 84 fe lw a2,-24(s0)
0x00010192 <call_me+70>: 83 25 c4 fe lw a1,-20(s0)
0x00010196 <call_me+74>: 61 65 lui a0,0x18
0x00010198 <call_me+76>: 13 05 85 6a addi a0,a0,1704
0x0001019c <call_me+80>: f1 22 jal 0x10368 <printf>
End of assembler dump.
And here's an example after this patch:
(gdb) disassemble /r 0x0001018e,0x0001019e
Dump of assembler code from 0x1018e to 0x1019e:
0x0001018e <call_me+66>: fe842603 lw a2,-24(s0)
0x00010192 <call_me+70>: fec42583 lw a1,-20(s0)
0x00010196 <call_me+74>: 6561 lui a0,0x18
0x00010198 <call_me+76>: 6a850513 addi a0,a0,1704
0x0001019c <call_me+80>: 22f1 jal 0x10368 <printf>
End of assembler dump.
There are two differences here. First, the instruction bytes after
the patch are grouped based on the size of the instruction, and are
byte-swapped to little-endian order.
Second, after the patch, GDB now uses the bytes-per-line hint from
libopcodes to add whitespace padding after the opcode bytes, this
means that in most cases the instructions are nicely aligned.
It is still possible for a very long instruction to intrude into the
disassembled text space. The next example is x86-64, before the
patch:
(gdb) disassemble /r main
Dump of assembler code for function main:
0x0000000000401106 <+0>: 55 push %rbp
0x0000000000401107 <+1>: 48 89 e5 mov %rsp,%rbp
0x000000000040110a <+4>: c7 87 d8 00 00 00 01 00 00 00 movl $0x1,0xd8(%rdi)
0x0000000000401114 <+14>: b8 00 00 00 00 mov $0x0,%eax
0x0000000000401119 <+19>: 5d pop %rbp
0x000000000040111a <+20>: c3 ret
End of assembler dump.
And after the patch:
(gdb) disassemble /r main
Dump of assembler code for function main:
0x0000000000401106 <+0>: 55 push %rbp
0x0000000000401107 <+1>: 48 89 e5 mov %rsp,%rbp
0x000000000040110a <+4>: c7 87 d8 00 00 00 01 00 00 00 movl $0x1,0xd8(%rdi)
0x0000000000401114 <+14>: b8 00 00 00 00 mov $0x0,%eax
0x0000000000401119 <+19>: 5d pop %rbp
0x000000000040111a <+20>: c3 ret
End of assembler dump.
Most instructions are aligned, except for the very long instruction.
Notice too that for x86-64 libopcodes doesn't request that GDB group
the instruction bytes. This matches the behaviour of objdump.
In case the user really wants the old behaviour, I have added a new
modifier 'disassemble /b', this displays the instruction byte at a
time. For x86-64, which never groups instruction bytes, /b and /r are
equivalent, but for RISC-V, using /b gets the old layout back (except
that the whitespace for alignment is still present). Consider our
original RISC-V example, this time using /b:
(gdb) disassemble /b 0x0001018e,0x0001019e
Dump of assembler code from 0x1018e to 0x1019e:
0x0001018e <call_me+66>: 03 26 84 fe lw a2,-24(s0)
0x00010192 <call_me+70>: 83 25 c4 fe lw a1,-20(s0)
0x00010196 <call_me+74>: 61 65 lui a0,0x18
0x00010198 <call_me+76>: 13 05 85 6a addi a0,a0,1704
0x0001019c <call_me+80>: f1 22 jal 0x10368 <printf>
End of assembler dump.
Obviously, this patch is a potentially significant change to the
behaviour or /r. I could have added /b with the new behaviour and
left /r alone. However, personally, I feel the new behaviour is
significantly better than the old, hence, I made /r be what I consider
the "better" behaviour.
The reason I prefer the new behaviour is that, when I use /r, I almost
always want to manually decode the instruction for some reason, and
having the bytes displayed in "instruction order" rather than memory
order, just makes this easier.
The 'record instruction-history' command also takes a /r modifier, and
has been modified in the same way as disassemble; /r gets the new
behaviour, and /b has been added to retain the old behaviour.
Finally, the MI command -data-disassemble, is unchanged in behaviour,
this command now requests the raw bytes of the instruction, which is
equivalent to the /b modifier. This means that the MI output will
remain backward compatible.
Diff:
---
gdb/NEWS | 12 +++++++++
gdb/cli/cli-cmds.c | 6 +++++
gdb/disasm-flags.h | 1 +
gdb/disasm.c | 43 ++++++++++++++++++++++++++---
gdb/doc/gdb.texinfo | 48 ++++++++++++++++++++++++++++-----
gdb/mi/mi-cmd-disas.c | 6 ++---
gdb/record.c | 3 +++
gdb/testsuite/gdb.mi/mi-disassemble.exp | 6 ++---
8 files changed, 109 insertions(+), 16 deletions(-)
diff --git a/gdb/NEWS b/gdb/NEWS
index 1457c99ff04..796a4ef8072 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -59,6 +59,18 @@
* gdb now supports zstd compressed debug sections (ELFCOMPRESS_ZSTD) for ELF.
+* The format of 'disassemble /r' and 'record instruction-history /r'
+ has changed. The instruction bytes could now be grouped together,
+ and displayed in the endianness of the instruction. This is the
+ same layout as used by GNU objdump when disassembling.
+
+ There is now 'disassemble /b' and 'record instruction-history /b'
+ which will always display the instructions bytes one at a time in
+ memory order, that is, the byte at the lowest address first.
+
+ For both /r and /b GDB is now better at using whitespace in order to
+ align the disassembled instruction text.
+
* New commands
maintenance set ignore-prologue-end-flag on|off
diff --git a/gdb/cli/cli-cmds.c b/gdb/cli/cli-cmds.c
index d5707192be0..c78b93f57b5 100644
--- a/gdb/cli/cli-cmds.c
+++ b/gdb/cli/cli-cmds.c
@@ -1508,6 +1508,9 @@ disassemble_current_function (gdb_disassembly_flags flags)
A /r modifier will include raw instructions in hex with the assembly.
+ A /b modifier is similar to /r except the instruction bytes are printed
+ as separate bytes with no grouping, or endian switching.
+
A /s modifier will include source code with the assembly, like /m, with
two important differences:
1) The output is still in pc address order.
@@ -1546,6 +1549,9 @@ disassemble_command (const char *arg, int from_tty)
case 'r':
flags |= DISASSEMBLY_RAW_INSN;
break;
+ case 'b':
+ flags |= DISASSEMBLY_RAW_BYTES;
+ break;
case 's':
flags |= DISASSEMBLY_SOURCE;
break;
diff --git a/gdb/disasm-flags.h b/gdb/disasm-flags.h
index 025b6893941..5a7371b0a39 100644
--- a/gdb/disasm-flags.h
+++ b/gdb/disasm-flags.h
@@ -33,6 +33,7 @@ enum gdb_disassembly_flag
DISASSEMBLY_OMIT_PC = (0x1 << 4),
DISASSEMBLY_SOURCE = (0x1 << 5),
DISASSEMBLY_SPECULATIVE = (0x1 << 6),
+ DISASSEMBLY_RAW_BYTES = (0x1 << 7),
};
DEF_ENUM_FLAGS_TYPE (enum gdb_disassembly_flag, gdb_disassembly_flags);
diff --git a/gdb/disasm.c b/gdb/disasm.c
index ba6ac2d4827..b5e503fd71d 100644
--- a/gdb/disasm.c
+++ b/gdb/disasm.c
@@ -457,7 +457,7 @@ gdb_pretty_print_disassembler::pretty_print_insn (const struct disasm_insn *insn
throw ex;
}
- if (flags & DISASSEMBLY_RAW_INSN)
+ if ((flags & (DISASSEMBLY_RAW_INSN | DISASSEMBLY_RAW_BYTES)) != 0)
{
/* Build the opcodes using a temporary stream so we can
write them out in a single go for the MI. */
@@ -467,14 +467,51 @@ gdb_pretty_print_disassembler::pretty_print_insn (const struct disasm_insn *insn
m_opcode_data.resize (size);
read_code (pc, m_opcode_data.data (), size);
- for (int i = 0; i < size; ++i)
+ /* The disassembler provides information about the best way to
+ display the instruction bytes to the user. We provide some sane
+ defaults in case the disassembler gets it wrong. */
+ const struct disassemble_info *di = m_di.disasm_info ();
+ int bytes_per_line = std::max (di->bytes_per_line, size);
+ int bytes_per_chunk = std::max (di->bytes_per_chunk, 1);
+
+ /* If the user has requested the instruction bytes be displayed
+ byte at a time, then handle that here. Also, if the instruction
+ is not a multiple of the chunk size (which probably indicates a
+ disassembler problem) then avoid that causing display problems
+ by switching to byte at a time mode. */
+ if ((flags & DISASSEMBLY_RAW_BYTES) != 0
+ || (size % bytes_per_chunk) != 0)
+ bytes_per_chunk = 1;
+
+ /* Print the instruction opcodes bytes, grouped into chunks. */
+ for (int i = 0; i < size; i += bytes_per_chunk)
{
if (i > 0)
m_opcode_stb.puts (" ");
- m_opcode_stb.printf ("%02x", (unsigned) m_opcode_data[i]);
+
+ if (di->display_endian == BFD_ENDIAN_LITTLE)
+ {
+ for (int k = bytes_per_chunk; k-- != 0; )
+ m_opcode_stb.printf ("%02x", (unsigned) m_opcode_data[i + k]);
+ }
+ else
+ {
+ for (int k = 0; k < bytes_per_chunk; k++)
+ m_opcode_stb.printf ("%02x", (unsigned) m_opcode_data[i + k]);
+ }
+ }
+
+ /* Calculate required padding. */
+ int nspaces = 0;
+ for (int i = size; i < bytes_per_line; i += bytes_per_chunk)
+ {
+ if (i > size)
+ nspaces++;
+ nspaces += bytes_per_chunk * 2;
}
m_uiout->field_stream ("opcodes", m_opcode_stb);
+ m_uiout->spaces (nspaces);
m_uiout->text ("\t");
}
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index 238a49b027d..596e5873558 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -7945,7 +7945,10 @@ are printed in execution order.
It can also print mixed source+disassembly if you specify the the
@code{/m} or @code{/s} modifier, and print the raw instructions in hex
-as well as in symbolic form by specifying the @code{/r} modifier.
+as well as in symbolic form by specifying the @code{/r} or @code{/b}
+modifier. The behaviour of the @code{/m}, @code{/s}, @code{/r}, and
+@code{/b} modifiers are the same as for the @kbd{disassemble} command
+(@pxref{disassemble,,@kbd{disassemble}}).
The current position marker is printed for the instruction at the
current program counter value. This instruction can appear multiple
@@ -9859,6 +9862,7 @@ After @code{info line}, using @code{info line} again without
specifying a location will display information about the next source
line.
+@anchor{disassemble}
@table @code
@kindex disassemble
@cindex assembly instructions
@@ -9869,16 +9873,17 @@ line.
@itemx disassemble /m
@itemx disassemble /s
@itemx disassemble /r
+@itemx disassemble /b
This specialized command dumps a range of memory as machine
instructions. It can also print mixed source+disassembly by specifying
-the @code{/m} or @code{/s} modifier and print the raw instructions in hex
-as well as in symbolic form by specifying the @code{/r} modifier.
-The default memory range is the function surrounding the
+the @code{/m} or @code{/s} modifier and print the raw instructions in
+hex as well as in symbolic form by specifying the @code{/r} or @code{/b}
+modifier. The default memory range is the function surrounding the
program counter of the selected frame. A single argument to this
command is a program counter value; @value{GDBN} dumps the function
-surrounding this value. When two arguments are given, they should
-be separated by a comma, possibly surrounded by whitespace. The
-arguments specify a range of addresses to dump, in one of two forms:
+surrounding this value. When two arguments are given, they should be
+separated by a comma, possibly surrounded by whitespace. The arguments
+specify a range of addresses to dump, in one of two forms:
@table @code
@item @var{start},@var{end}
@@ -9916,6 +9921,35 @@ Dump of assembler code from 0x32c4 to 0x32e4:
End of assembler dump.
@end smallexample
+The following two examples are for RISC-V, and demonstrates the
+difference between the @code{/r} and @code{/b} modifiers. First with
+@code{/b}, the bytes of the instruction are printed, in hex, in memory
+order:
+
+@smallexample
+(@value{GDBP}) disassemble /b 0x00010150,0x0001015c
+Dump of assembler code from 0x10150 to 0x1015c:
+ 0x00010150 <call_me+4>: 22 dc sw s0,56(sp)
+ 0x00010152 <call_me+6>: 80 00 addi s0,sp,64
+ 0x00010154 <call_me+8>: 23 26 a4 fe sw a0,-20(s0)
+ 0x00010158 <call_me+12>: 23 24 b4 fe sw a1,-24(s0)
+End of assembler dump.
+@end smallexample
+
+In contrast, with @code{/r} the bytes of the instruction are displayed
+in the instruction order, for RISC-V this means that the bytes have been
+swapped to little-endian order:
+
+@smallexample
+(@value{GDBP}) disassemble /r 0x00010150,0x0001015c
+Dump of assembler code from 0x10150 to 0x1015c:
+ 0x00010150 <call_me+4>: dc22 sw s0,56(sp)
+ 0x00010152 <call_me+6>: 0080 addi s0,sp,64
+ 0x00010154 <call_me+8>: fea42623 sw a0,-20(s0)
+ 0x00010158 <call_me+12>: feb42423 sw a1,-24(s0)
+End of assembler dump.
+@end smallexample
+
Here is an example showing mixed source+assembly for Intel x86
with @code{/m} or @code{/s}, when the program is stopped just after
function prologue in a non-optimized function with no inline code.
diff --git a/gdb/mi/mi-cmd-disas.c b/gdb/mi/mi-cmd-disas.c
index 387c4900150..c8e06cd940a 100644
--- a/gdb/mi/mi-cmd-disas.c
+++ b/gdb/mi/mi-cmd-disas.c
@@ -165,16 +165,16 @@ mi_cmd_disassemble (const char *command, char **argv, int argc)
disasm_flags |= DISASSEMBLY_SOURCE_DEPRECATED;
break;
case 2:
- disasm_flags |= DISASSEMBLY_RAW_INSN;
+ disasm_flags |= DISASSEMBLY_RAW_BYTES;
break;
case 3:
- disasm_flags |= DISASSEMBLY_SOURCE_DEPRECATED | DISASSEMBLY_RAW_INSN;
+ disasm_flags |= DISASSEMBLY_SOURCE_DEPRECATED | DISASSEMBLY_RAW_BYTES;
break;
case 4:
disasm_flags |= DISASSEMBLY_SOURCE;
break;
case 5:
- disasm_flags |= DISASSEMBLY_SOURCE | DISASSEMBLY_RAW_INSN;
+ disasm_flags |= DISASSEMBLY_SOURCE | DISASSEMBLY_RAW_BYTES;
break;
default:
gdb_assert_not_reached ("bad disassembly mode");
diff --git a/gdb/record.c b/gdb/record.c
index 17a5df262bd..2390a58f9c0 100644
--- a/gdb/record.c
+++ b/gdb/record.c
@@ -494,6 +494,9 @@ get_insn_history_modifiers (const char **arg)
case 'r':
modifiers |= DISASSEMBLY_RAW_INSN;
break;
+ case 'b':
+ modifiers |= DISASSEMBLY_RAW_BYTES;
+ break;
case 'f':
modifiers |= DISASSEMBLY_OMIT_FNAME;
break;
diff --git a/gdb/testsuite/gdb.mi/mi-disassemble.exp b/gdb/testsuite/gdb.mi/mi-disassemble.exp
index b7c52472c84..ef3337d4062 100644
--- a/gdb/testsuite/gdb.mi/mi-disassemble.exp
+++ b/gdb/testsuite/gdb.mi/mi-disassemble.exp
@@ -245,12 +245,12 @@ proc test_disassembly_opcode_format {} {
# then disassemble using the MI command.
set longest_insn_bytes ""
set longest_insn_addr ""
- gdb_test_multiple "disassemble /r main" "" {
- -re "^disassemble /r main\r\n" {
+ gdb_test_multiple "disassemble /b main" "" {
+ -re "^disassemble /b main\r\n" {
exp_continue
}
- -re "^&\"disassemble /r main.n\"\r\n" {
+ -re "^&\"disassemble /b main.n\"\r\n" {
exp_continue
}
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