Re: [PATCH] [gdb/testsuite] Fix gdb.base/vla-optimized-out.exp for ppc64le

[Carl Love <cel@us.ibm.com>]

Tom:

I looked at this issue as well some time ago.  I also found that the
issue was due to the value being optimized out. The fix looks good to
me.  I verified that it fixes the issue on my Power 10 machine. 
Thanks.

                    Carl 


On Tue, 2022-11-29 at 14:32 +0100, Tom de Vries wrote:
> From: Tom de Vries <tdevries@loganberry-1.arch.suse.de>
> 
> On powerpc64le-linux, I run into:
> ...
> (gdb) PASS: gdb.base/vla-optimized-out.exp: o1: printed optimized out
> vla
> p sizeof (a)^M
> $2 = <optimized out>^M
> (gdb) FAIL: gdb.base/vla-optimized-out.exp: o1: \
>   printed size of optimized out vla
> ...
> 
> The problem happens as follows.
> 
> In order to find the size of the optimized out vla, gdb needs to
> evaluate:
> ...
> <155> DW_AT_upper_bound : 13 byte block: f3 1 53 23 1 8 20 24 8 20 26
> 31 1c \
>   (DW_OP_GNU_entry_value: (DW_OP_reg3 (r3)); DW_OP_plus_uconst: 1;
>    DW_OP_const1u: 32; DW_OP_shl; DW_OP_const1u: 32; DW_OP_shra;
> DW_OP_lit1;
>    DW_OP_minus)
> ...
> 
> When trying to evaluate DW_OP_GNU_entry_value, it looks for a call
> site
> matching the pc, but doesn't find it:
> ...
> $ gdb -q -batch outputs/gdb.base/vla-optimized-out/vla-optimized-out-
> o1 \
>   -ex "break f1" -ex run -ex "set debug entry-values 1" -ex "print
> sizeof (a)"
> Breakpoint 1 at 0x1000067c: file vla-optimized-out.c, line 34.
> 
> Breakpoint 1, f1 (i=5) at vla-optimized-out.c:34
> 34      }
> DW_OP_entry_value resolving cannot find DW_TAG_call_site 0x100006b0
> in main
> $1 = <optimized out>
> ....
> 
> The call site lookup fails because the call site label .LVL4:
> ...
>         bl f1    # 11   *call_value_nonlocal_aixdi      [length = 8]
>         nop
> .LVL4:
> ...
> is not placed directly after the bl insn.  This is gcc PR
> target/107909.
> 
> However, after manually fixing the .s file we have instead:
> ...
> Cannot find matching parameter at DW_TAG_call_site 0x10000690 at main
> $1 = <optimized out>
> ...
> due to the fact that the call site has no call site parameters.
> 
> The call site does have a reference to the corresponding function f1,
> with
> parameter i, for which we find location list entries:
> ...
>   0037 1000067c 10000680 (DW_OP_reg3 (r3))
>   004a 10000680 10000690 (DW_OP_GNU_entry_value: (DW_OP_reg3 (r3));
>                           DW_OP_stack_value)
> ...
> and we could use the fact that the current pc is in the 1000067c-
> 10000680
> range, and that that the range starts at the start of the function,
> to deduce
> that DW_OP_GNU_entry_value: (DW_OP_reg3 (r3)) == DW_OP_reg3 (r3).
> But that's a non-trivial enhancement, filed as enhancement PR
> symtab/29836.
> 
> Fix this by allowing <optimized out> for target powerpc and the gcc
> compiler.
> 
> PR testsuite/29813
> Bug: 
> https://sourceware.org/bugzilla/show_bug.cgi?id=29813
>  
> ---
>  gdb/testsuite/gdb.base/vla-optimized-out.exp | 23 +++++++++++++++---
> --
>  1 file changed, 17 insertions(+), 6 deletions(-)
> 
> diff --git a/gdb/testsuite/gdb.base/vla-optimized-out.exp
> b/gdb/testsuite/gdb.base/vla-optimized-out.exp
> index b16142ee329..b897ea8124c 100644
> --- a/gdb/testsuite/gdb.base/vla-optimized-out.exp
> +++ b/gdb/testsuite/gdb.base/vla-optimized-out.exp
> @@ -67,12 +67,23 @@ proc vla_optimized_out {exe_suffix options} {
>  	"print out of range element of vla (0xffffffff)"
>  }
>  
> -foreach {test_prefix options} \
> -    { "o1" {{debug optimize=-O1 additional_flags=-DNOCLONE} "6"} \
> -      "o3" {{debug optimize=-O3} "<optimized out>|6"} \
> -      "o3_strict" {{debug optimize=-O3 \
> -			additional_flags=-gstrict-dwarf} \
> -		       "<optimized out>|6"}} {
> +set o1_sizeof_result "6"
> +if { [istarget powerpc*-*-*] && [gcc_major_version] != -1 } {
> +    set o1_sizeof_result "<optimized out>|6"
> +}
> +
> +set test_matrix {}
> +lappend test_matrix \
> +    "o1" \
> +    [list {debug optimize=-O1 additional_flags=-DNOCLONE}
> $o1_sizeof_result]
> +lappend test_matrix \
> +    "o3" \
> +    {{debug optimize=-O3} "<optimized out>|6"}
> +lappend test_matrix \
> +    "o3_strict" \
> +    {{debug optimize=-O3 additional_flags=-gstrict-dwarf}
> "<optimized out>|6"}
> +
> +foreach {test_prefix options} $test_matrix {
>      with_test_prefix $test_prefix {
>  	vla_optimized_out $test_prefix $options
>      }