Re: [PATCH 3/4] [gdb/tdep, aarch64] Fix frame address of last insn in leaf function

[Luis Machado <luis.machado@arm.com>]

On 1/23/23 11:59, Tom de Vries wrote:
> On 1/23/23 11:07, Luis Machado wrote:
>> On 1/19/23 10:46, Tom de Vries wrote:
>>> Consider the test-case test.c, compiled without debug info:
>>> ...
>>> void
>>> foo (const char *s)
>>> {
>>> }
>>>
>>> int
>>> main (void)
>>> {
>>>    foo ("foo");
>>>    return 0;
>>> }
>>> ...
>>>
>>> Disassembly of foo:
>>> ...
>>> 0000000000400564 <foo>:
>>>    400564:       d10043ff        sub     sp, sp, #0x10
>>>    400568:       f90007e0        str     x0, [sp, #8]
>>>    40056c:       d503201f        nop
>>>    400570:       910043ff        add     sp, sp, #0x10
>>>    400574:       d65f03c0        ret
>>> ...
>>>
>>> Now, let's do "info frame" at each insn in foo, as well as printing $sp
>>> and $x29 (and strip the output of info frame to the first line, for brevity):
>>> ...
>>> $ gdb -q a.out
>>> Reading symbols from a.out...
>>> (gdb) b *foo
>>> Breakpoint 1 at 0x400564
>>> (gdb) r
>>> Starting program: a.out
>>>
>>> Breakpoint 1, 0x0000000000400564 in foo ()
>>> (gdb) display /x $sp
>>> 1: /x $sp = 0xfffffffff3a0
>>> (gdb) display /x $x29
>>> 2: /x $x29 = 0xfffffffff3a0
>>> (gdb) info frame
>>> Stack level 0, frame at 0xfffffffff3a0:
>>> (gdb) si
>>> 0x0000000000400568 in foo ()
>>> 1: /x $sp = 0xfffffffff390
>>> 2: /x $x29 = 0xfffffffff3a0
>>> (gdb) info frame
>>> Stack level 0, frame at 0xfffffffff3a0:
>>> (gdb) si
>>> 0x000000000040056c in foo ()
>>> 1: /x $sp = 0xfffffffff390
>>> 2: /x $x29 = 0xfffffffff3a0
>>> (gdb) info frame
>>> Stack level 0, frame at 0xfffffffff3a0:
>>> (gdb) si
>>> 0x0000000000400570 in foo ()
>>> 1: /x $sp = 0xfffffffff390
>>> 2: /x $x29 = 0xfffffffff3a0
>>> (gdb) info frame
>>> Stack level 0, frame at 0xfffffffff3a0:
>>> (gdb) si
>>> 0x0000000000400574 in foo ()
>>> 1: /x $sp = 0xfffffffff3a0
>>> 2: /x $x29 = 0xfffffffff3a0
>>> (gdb) info frame
>>> Stack level 0, frame at 0xfffffffff3b0:
>>>   pc = 0x400574 in foo; saved pc = 0x40058c
>>> (gdb) si
>>> 0x000000000040058c in main ()
>>> 1: /x $sp = 0xfffffffff3a0
>>> 2: /x $x29 = 0xfffffffff3a0
>>> ...
>>>
>>> The "frame at" bit lists 0xfffffffff3a0 except at the last insn, where it
>>> lists 0xfffffffff3b0.
>>>
>>> The frame address is calculated here in aarch64_make_prologue_cache_1:
>>> ...
>>>    unwound_fp = get_frame_register_unsigned (this_frame, cache->framereg);
>>>    if (unwound_fp == 0)
>>>      return;
>>>
>>>    cache->prev_sp = unwound_fp + cache->framesize;
>>> ...
>>>
>>> For insns after the prologue, we have cache->framereg == sp and
>>> cache->framesize == 16, so unwound_fp + cache->framesize gives the wrong
>>> answer once sp has been restored to entry value by the before-last insn.
>>>
>>> Fix this by detecting the situation that the sp has been restored.
>>>
>>> This fixes PR tdep/30011.
>>>
>>> This also fixes the aarch64 FAILs in gdb.reverse/solib-precsave.exp and
>>> gdb.reverse/solib-reverse.exp I reported in PR gdb/PR29721.
>>
>> I still see failures for gdb.reverse/solib-precsave.exp and gdb.reverse/solib-reverse.exp for both Ubuntu 22.04 and 20.04
>> on aarch64-linux.
>>
>> Running /work/luimac01/work/builds/binutils-gdb-arm64-jammy/gdb/testsuite/../../../../repos/binutils-gdb/gdb/testsuite/gdb.reverse/solib-prec
>> save.exp ...
>> FAIL: gdb.reverse/solib-precsave.exp: reverse-step into solib function one
>> FAIL: gdb.reverse/solib-precsave.exp: reverse-step within solib function one
>> FAIL: gdb.reverse/solib-precsave.exp: reverse-step back to main one
>> FAIL: gdb.reverse/solib-precsave.exp: reverse-step into solib function two
>> FAIL: gdb.reverse/solib-precsave.exp: reverse-step within solib function two
>>
>> Running /work/luimac01/work/builds/binutils-gdb-arm64-jammy/gdb/testsuite/../../../../repos/binutils-gdb/gdb/testsuite/gdb.reverse/solib-reve
>> rse.exp ...
>> FAIL: gdb.reverse/solib-reverse.exp: reverse-step into solib function one
>> FAIL: gdb.reverse/solib-reverse.exp: reverse-step within solib function one
>> FAIL: gdb.reverse/solib-reverse.exp: reverse-step back to main one
>> FAIL: gdb.reverse/solib-reverse.exp: reverse-step into solib function two
>> FAIL: gdb.reverse/solib-reverse.exp: reverse-step within solib function two
>>
>> Maybe it addresses a different issue, but what I'm seeing is possibly something else (the linetable issue? I vaguely recall the situation for that).
>>>
> 
> Hi,
> 
> that is very well possible.  I'm not claiming to fix the test-case on aarch64 in general, I'm very specifically claiming to fix the FAILs I reported in a PR.
> 
> BTW the first FAIL in the PR is also different than the one you report above, which is usually a hint that there may be a different root cause.
> 
> I'll commit (using an updated commit message claiming both PRs tdep/30010 and tdep/30011) once I do another round of testing.
> 
> Thanks,
> - Tom
> 

Sounds good to me. Thanks for the patch.