[Bug c/57838] New: GCC does not obey #pragma long_calls with builtins and -Os on cortexM3

[zgtamuam84 at snkmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57838

            Bug ID: 57838
           Summary: GCC does not obey #pragma long_calls with builtins and
                    -Os on cortexM3
           Product: gcc
           Version: 4.7.3
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: zgtamuam84 at snkmail dot com

Created attachment 30470
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=30470&action=edit
C code

I am compiling an application for the cortexM3 where stdlib is in ROM and the
applictaion runs in RAM.  To call ROM from RAM I need to use long-calls.

so I build as follows:

gcc -mcpu=cortex-m3 -mthumb -Wall -Wextra -std=gnu99 -Os -c test.c

The resulting disassembly shows that memset wasn't called via a long-call
method:
test.o:     file format elf32-littlearm


Disassembly of section .text.startup:

Disassembly of section .text.startup:

00000000 <main>:
   0:    b508          push    {r3, lr}
   2:    f7ff fffe     bl    0 <tfunc>
   6:    2100          movs    r1, #0
   8:    2264          movs    r2, #100    ; 0x64
   a:    4802          ldr    r0, [pc, #8]    ; (14 <main+0x14>)
   c:    f7ff fffe     bl    0 <memset>
  10:    2000          movs    r0, #0
  12:    bd08          pop    {r3, pc}
  14:    00000000     .word    0x00000000

The tfunc() call is a short-jump as expected, but the memset() call is also
short which is not expected.

removing -Os, or compiling with -fno-builtin or removing the #pragma
no_long_calls all work-around the issue and generate a long-call to memset().

In my application, I want non standard-lib functions to use short-calls (thus
the '#pragma no_long_calls' after header inclusion), and I want builtins to be
used when possible (thus I don't want to use -fno-builtin)

I have tested on gcc 4.6.2 and 4.7.3, both of which exhibit this behavior.