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202be274a4
While working on another patch[1] I had need to touch this code in
i386-dis.c:
ins->obufp = ins->mnemonicendp;
for (i = strlen (ins->obuf) + prefix_length; i < 6; i++)
oappend (ins, " ");
oappend (ins, " ");
(*ins->info->fprintf_styled_func)
(ins->info->stream, dis_style_mnemonic, "%s", ins->obuf);
What this code does is add whitespace after the instruction mnemonic
and before the instruction operands.
The problem I ran into when working on this code can be seen by
assembling this input file:
.text
nop
retq
Now, when I disassemble, here's the output. I've replaced trailing
whitespace with '_' so that the issue is clearer:
Disassembly of section .text:
0000000000000000 <.text>:
0: 90 nop
1: c3 retq___
Notice that there's no trailing whitespace after 'nop', but there are
three spaces after 'retq'!
What happens is that instruction mnemonics are emitted into a buffer
instr_info::obuf, then instr_info::mnemonicendp is setup to point to
the '\0' character at the end of the mnemonic.
When we emit the whitespace, this is then added starting at the
mnemonicendp position. Lets consider 'retq', first the buffer is
setup like this:
'r' 'e' 't' 'q' '\0'
Then we add whitespace characters at the '\0', converting the buffer
to this:
'r' 'e' 't' 'q' ' ' ' ' ' ' '\0'
However, 'nop' is actually an alias for 'xchg %rax,%rax', so,
initially, the buffer is setup like this:
'x' 'c' 'h' 'g' '\0'
Then in NOP_Fixup we spot that we have an instruction that is an alias
for 'nop', and adjust the buffer to this:
'n' 'o' 'p' '\0' '\0'
The second '\0' is left over from the original buffer contents.
However, when we rewrite the buffer, we don't afjust mnemonicendp,
which still points at the second '\0' character.
Now, when we insert whitespace we get:
'n' 'o' 'p' '\0' ' ' ' ' ' ' ' ' '\0'
Notice the whitespace is inserted after the first '\0', so, when we
print the buffer, the whitespace is not printed.
The fix for this is pretty easy, I can change NOP_Fixup to adjust
mnemonicendp, but now a bunch of tests start failing, we now produce
whitespace after the 'nop', which the tests don't expect.
So, I could update the tests to expect the whitespace....
...except I'm not a fan of trailing whitespace, so I'd really rather
not.
Turns out, I can pretty easily update the whitespace emitting code to
spot instructions that have zero operands and just not emit any
whitespace in this case. So this is what I've done.
I've left in the fix for NOP_Fixup, I think updating mnemonicendp is
probably a good thing, though this is not really required any more.
I've then updated all the tests that I saw failing to adjust the
expected patterns to account for the change in whitespace.
[1] https://sourceware.org/pipermail/binutils/2022-April/120610.html
125 lines
3.6 KiB
Plaintext
125 lines
3.6 KiB
Plaintext
# Copyright 2016-2022 Free Software Foundation, Inc.
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#
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# This program is free software; you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation; either version 3 of the License, or
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# (at your option) any later version.
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#
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License
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# along with this program. If not, see <http://www.gnu.org/licenses/>.
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standard_testfile
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# Test a thread is doing step-over a syscall instruction which is exit,
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# and GDBserver should cleanup its state of step-over properly.
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set syscall_insn ""
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# Define the syscall instruction for each target.
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if { [istarget "i\[34567\]86-*-linux*"] || [istarget "x86_64-*-linux*"] } {
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set syscall_insn "\[ \t\](int|syscall|sysenter)\[ \t\]*"
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} elseif { [istarget "aarch64*-*-linux*"] || [istarget "arm*-*-linux*"] } {
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set syscall_insn "\[ \t\](swi|svc)\[ \t\]"
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} else {
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unsupported "unknown syscall instruction"
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return -1
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}
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if {[prepare_for_testing "failed to prepare" $testfile $srcfile debug]} {
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return -1
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}
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if ![runto_main] {
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return -1
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}
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gdb_test "set follow-fork-mode child"
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gdb_test "set detach-on-fork off"
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# Step 1, find the syscall instruction address.
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gdb_test "break _exit" "Breakpoint $decimal at .*"
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# Hit the breakpoint on _exit. The address of syscall insn is recorded.
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gdb_test "continue" \
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"Continuing\\..*Breakpoint $decimal.*_exit \\(.*\\).*" \
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"continue to exit"
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gdb_test "display/i \$pc" ".*"
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# Single step until we see a syscall insn or we reach the
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# upper bound of loop iterations.
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set msg "find syscall insn in exit"
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set steps 0
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set max_steps 1000
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gdb_test_multiple "stepi" $msg {
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-re ".*$syscall_insn.*$gdb_prompt $" {
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pass $msg
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}
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-re "x/i .*=>.*\r\n$gdb_prompt $" {
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incr steps
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if {$steps == $max_steps} {
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fail $msg
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} else {
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send_gdb "stepi\n"
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exp_continue
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}
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}
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}
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if {$steps == $max_steps} {
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return
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}
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# Remove the display
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gdb_test_no_output "delete display 1"
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set syscall_insn_addr [get_hexadecimal_valueof "\$pc" "0"]
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gdb_test "continue" "exited normally.*" "continue to end, first time"
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gdb_test "inferior 1" ".*Switching to inferior 1.*" \
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"switch back to inferior 1, first time"
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delete_breakpoints
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gdb_test "break marker"
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gdb_test "continue" "Continuing\\..*Breakpoint $decimal, .*" \
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"continue to marker, first time"
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# Step 2, create a breakpoint which evaluates false, and force it
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# evaluated on the target side.
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set test "set breakpoint condition-evaluation target"
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gdb_test_multiple $test $test {
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-re "warning: Target does not support breakpoint condition evaluation.\r\nUsing host evaluation mode instead.\r\n$gdb_prompt $" {
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# Target doesn't support breakpoint condition evaluation
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# on its side, but it is no harm to run the test.
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}
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-re "^$test\r\n$gdb_prompt $" {
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}
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}
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gdb_test "break \*$syscall_insn_addr if main == 0" \
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"Breakpoint \[0-9\]* at .*" \
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"set conditional break at syscall address"
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# Resume the child process, and the step-over is being done.
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gdb_test "continue" "exited normally.*" "continue to end, second time"
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gdb_test "inferior 1" ".*Switching to inferior 1.*" \
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"switch back to inferior 1, second time"
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# Switch back to the parent process, continue to the marker to
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# test GDBserver's state is still correct.
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gdb_test "continue" "Continuing\\..*Breakpoint $decimal, .*" \
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"continue to marker, second time"
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