[Bug target/94134] pdp11-aout puts initial variable into .text section rather than .data

[casner at acm dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94134

Stephen Casner <casner at acm dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Target|                            |pdp11-aout

--- Comment #1 from Stephen Casner <casner at acm dot org> ---
I would be happy to work on implementing a fix for this bug if someone can
point me in the right direction.  I tried defining a TARGET_ASM_SELECT_SECTION
function for the pdp11-aout target that always returns data_section, but the
result was unchanged.  I verified that function was only called once when
compiling my test program, that was at the point the .data directive was
emitted.

Then I stepped through the code in varasm.c to understand a bit about why this
happens.  Because the test program variable is not initialized to a nonzero
value, bss_initializer_p returns true, and consequently get_variable_section
returns lcomm_section.  Because lcomm_section is of style SECTION_NOSWITCH,
assemble_variable calls assemble_noswitch_variable to generate the output
rather than calling switch_to_section and assemble_variable_contents as is what
happens to generate the .data directive before my test program variable that
_is_ initialized to a nonzero value.

assemble_noswitch_variable generates the assembler output by calling the
callback of the section, which for lcomm_section is emit_local.  emit_local
calls ASM_OUTPUT_ALIGNED_LOCAL which has been defined for the pdp11-aout target
and implemented in pdp11_asm_output_var.  A partial fix might be to have that
function output a .bss directive ahead of the zero-initialized variable.  A
side comment is that I have not seen any .bss directive even in the output from
the real C program that led me to observe this bug.  But since we can't switch
in_section to lcomm_section, I don't know to avoid emitting .bss ahead of every
zero-initialized (or uninitialized) variable even when there are several in a
row.  Furthermore, the comment for #define SECTION_NOSWITCH says that it is for
sections that we cannot switch to with an assembler directive (like .bss), so
perhaps the logic leading to the choice of lcomm_section is not appropriate for
the pdp11_aout target.

In addition, if the "static" is removed from the zero-initialized variable
declaration in my test program so it is global, then TREE_PUBLIC is true so it
is not assigned to the lcomm_section and instead falls through to be assigned
to the .data section.  It seems that zero-initialized variables should be
assigned to the same section whether local or global.