Re: [PATCH] Remove fno-unit-at-a-time make variable

[Fangrui Song <maskray@google.com>]

On 2022-03-30, Adhemerval Zanella wrote:
>
>
>On 30/03/2022 13:23, Fangrui Song wrote:
>> On 2022-03-30, Adhemerval Zanella wrote:
>>>
>>>
>>> On 30/03/2022 02:07, Fangrui Song wrote:
>>>> 795985e4e751 in 2003 added -fno-unit-at-a-time to errlist.c and
>>>> siglist.c to "avoid reordering assembler output". -fno-toplevel-reorder
>>>> is a rough replacement for this legacy option
>>>> (https://sourceware.org/pipermail/gcc-patches/2006-January/186801.html).
>>>>
>>>> The reordering requirement does not seem to be needed any longer.
>>>
>>> We still need them for otherwise DEFINE_COMPAT_ERRLIST used on errlist-compat.c
>>> does not create _sys_errlist and _sys_siglist with expected sizes defined by
>>> glibc ABI.
>>>
>>> I am trying to fix without resorting to compiler options.
>>
>> DEFINE_COMPAT_ERRLIST does not expand to code/data, just reordeable directives:
>>
>>
>>        .globl  __GLIBC_2_1_sys_errlist
>> .set __GLIBC_2_1_sys_errlist, _sys_errlist_internal
>>         .type   __GLIBC_2_1_sys_errlist,@object
>>         .size   __GLIBC_2_1_sys_errlist, 1000
>>         .globl  __GLIBC_2_1__sys_errlist
>> .set __GLIBC_2_1__sys_errlist, _sys_errlist_internal
>>         .type   __GLIBC_2_1__sys_errlist,@object
>>         .size   __GLIBC_2_1__sys_errlist, 1000
>> .symver __GLIBC_2_1_sys_nerr, sys_nerr@GLIBC_2.2.5
>> .symver __GLIBC_2_1__sys_nerr, _sys_nerr@GLIBC_2.2.5
>> .symver __GLIBC_2_1_sys_errlist, sys_errlist@GLIBC_2.2.5
>> .symver __GLIBC_2_1__sys_errlist, _sys_errlist@GLIBC_2.2.5
>>         .globl  __GLIBC_2_3_sys_errlist
>> .set __GLIBC_2_3_sys_errlist, _sys_errlist_internal
>>         .type   __GLIBC_2_3_sys_errlist,@object
>>         .size   __GLIBC_2_3_sys_errlist, 1008
>>         .globl  __GLIBC_2_3__sys_errlist
>> .set __GLIBC_2_3__sys_errlist, _sys_errlist_internal
>>         .type   __GLIBC_2_3__sys_errlist,@object
>>         .size   __GLIBC_2_3__sys_errlist, 1008
>> .symver __GLIBC_2_3_sys_nerr, sys_nerr@GLIBC_2.3
>> .symver __GLIBC_2_3__sys_nerr, _sys_nerr@GLIBC_2.3
>> .symver __GLIBC_2_3_sys_errlist, sys_errlist@GLIBC_2.3
>> .symver __GLIBC_2_3__sys_errlist, _sys_errlist@GLIBC_2.3
>>         .globl  __GLIBC_2_4_sys_errlist
>>
>> I do not know whether GCC would reorder these macros. Even yes,
>> that'd just change the .symtab entries in the relocatable object file.
>> The linker behavior remains the same with reordering.
>
>It does not seem to, just remove the -fno-unit-at-a-time and issue make
>check-abi and you will see that object size for the compat symbols
>reference to _sys_err_internal instead of the define compat ones.

I see. I think this is a brittle behavior in GNU assembler. Filed
https://sourceware.org/bugzilla/show_bug.cgi?id=29012 with detailed
information. I have created a patch but I know that will not solve
glibc's problem :(