Re: [PATCH] GDB: maint: Fix build on FreeBSD

[Thiago Jung Bauermann <thiago.bauermann@linaro.org>]

Hello Simon,

Simon Marchi <simark@simark.ca> writes:

> On 6/27/25 12:45 AM, Thiago Jung Bauermann wrote:
>> While trying to build current trunk of GDB on FreeBSD 14.3 on aarch64,
>> I hit this warning converted to an error:
>> 
>> In file included from /home/bauermann/src/binutils-gdb/gdb/maint.c:37:
>> /home/bauermann/src/binutils-gdb/gdb/maint.h:64:8: error: private field 'm_start_space' is not used [-Werror,-Wunused-private-field]
>>    64 |   long m_start_space;
>>       |        ^
>> 1 error generated.
>> gmake[2]: *** [Makefile:1973: maint.o] Error 1
>> 
>> I used the default compiler on this system:
>> 
>> $ c++ --version
>> FreeBSD clang version 19.1.7 (https://github.com/llvm/llvm-project.git llvmorg-19.1.7-0-gcd708029e0b2)
>> Target: aarch64-unknown-freebsd14.3
>> Thread model: posix
>> InstalledDir: /usr/bin
>> 
>> The problem is that the only two places that use m_start_space are
>> guarded by HAVE_USEFUL_SBRK, so also guard the member declaration with
>> it.
>> 
>> Build-tested on aarch64-unknown-freebsd14.3.
>
> I think there is nothing wrong with fixing the build, so:
>
> Approved-By: Simon Marchi <simon.marchi@efficios.com>

Thanks! Pushed as commit 48e0ec748443.

> But then, is this feature useful at all nowadays?  I don't have a deep
> knowledge of memory allocators work, but my understanding is that modern
> allocators use mmap to obtain more memory from the system (or they use
> both).  So the memory usage computed using sbrk would not be very
> accurate.  All of this to say that, if there is a metric we know is not
> accurate, it might be better to remove it.

I don't know much either, but my cursory research suggests you're right.

OTOH I would think it should be possible to obtain a "memory allocated
by GDB" number to use in place of the sbrk return result, so at least on
some platforms this metric can be fixed. For example, glibc provides the
malloc_info function, and Unix in general can use RSS.

Not that I'm volunteering to fix this code. :-)

-- 
Thiago