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

[Adhemerval Zanella <adhemerval.zanella@linaro.org>]

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.