Re: [PATCH][gdb/testsuite] Use prototype to call libc functions

[Kevin Buettner via Gdb-patches <gdb-patches@sourceware.org>]

On Mon, 5 Sep 2022 14:27:07 +0200
Tom de Vries via Gdb-patches <gdb-patches@sourceware.org> wrote:

> Hi,
> 
> On openSUSE Tumbleweed (using glibc 2.36), I run into:
> ...
> (gdb) print /d (int) munmap (4198400, 4096)^M
> Invalid cast.^M
> (gdb) FAIL: gdb.base/break-main-file-remove-fail.exp: cmdline: \
>   get integer valueof "(int) munmap (4198400, 4096)"
> ...
> 
> The problem is that after starting the executable, the symbol has type
> "void (*) (void)":
> ...
> (gdb) p munmap
> $1 = {<text variable, no debug info>} 0x401030 <munmap@plt>
> (gdb) start
>   ...
> (gdb) p munmap
> $2 = {void (void)} 0x7ffff7feb9a0 <__GI_munmap>
> ...
> which causes the "Invalid cast" error.
> 
> Looking at the debug info for glibc for symbol __GI_munmap:
> ...
>  <0><189683>: Abbrev Number: 1 (DW_TAG_compile_unit)
>     <189691>   DW_AT_name        : ../sysdeps/unix/syscall-template.S
>     <189699>   DW_AT_producer    : GNU AS 2.39.0
> <1><1896ae>: Abbrev Number: 2 (DW_TAG_subprogram)
>     <1896af>   DW_AT_name        : __GI___munmap
>     <1896b3>   DW_AT_external    : 1
>     <1896b4>   DW_AT_low_pc      : 0x10cad0
>     <1896bc>   DW_AT_high_pc     : 37
> ...
> that's probably caused by this bit (or similar bits for other munmap aliases).
> 
> This is fixed in gas on trunk by commit 5578fbf672e ("GAS: Add a return type
> tag to DWARF DIEs generated for function symbols").
> 
> Work around this (for say gas 2.39) by explicitly specifying the prototype for
> munmap.
> 
> Likewise for getpid in a couple of other test-cases.
> 
> Tested on x86_64-linux.
> 
> Any comments?

I have mixed feelings about patches like this.

One the one hand, it's nice to have the test "fixed" so that it doesn't
fail.

But, on the other hand, this failure found a problem with the debug info
in glibc, so fixing it as you did here will remove that test.

Perhaps you could add a new test which will still fail when the debug info
incorrectly specifies that munmap has a void return type?

Kevin