[Bug target/65416] New: xtensa: memory allocated by alloca is used before the stack pointer is updated

[jcmvbkbc at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65416

            Bug ID: 65416
           Summary: xtensa: memory allocated by alloca is used before the
                    stack pointer is updated
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jcmvbkbc at gcc dot gnu.org

Created attachment 35025
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=35025&action=edit
preprocessed source with a single function that demonstrates the issue

Hi,

I'm building gcc for xtensa linux. The function 'fork_inferior' has the
following fragment:

      argv = (char **) alloca (4 * sizeof (char *));
      argv[0] = shell_file;
      argv[1] = "-c";
      argv[2] = shell_command;
      argv[3] = (char *) 0;

that gcc compiles into this:

        addi    a3, sp, -32 
        l32r    a4, .LC23 
        s32i.n  a2, a3, 8 
        movi.n  a2, 0 
        s32i.n  a2, a3, 12 
        l32r    a2, .LC26 
        s32i.n  a3, a4, 0 
        l32i.n  a4, a7, 0 
        l32i.n  a2, a2, 0 
        s32i.n  a4, a3, 0 
        l32r    a4, .LC25 
        s32i.n  a2, a7, 20 
        l32i.n  a10, a7, 24 
        l32r    a2, .LC27 
        movsp   sp, a3 

Here argv is a3. The space below the stack pointer is used before the stack
pointer is updated.

This is reproducible with gcc-4.8.3 and the current 5.0 mainline.

Command line:
xtensa-buildroot-linux-uclibc-gcc -mlongcalls -mtext-section-literals -pipe -Os
-S -o fork-child.s fork-child.i

Compilers:

Using built-in specs.
COLLECT_GCC=/home/jcmvbkbc/tmp/br/build-xea3/host/usr/bin/xtensa-buildroot-linux-uclibc-gcc
COLLECT_LTO_WRAPPER=/home/jcmvbkbc/tmp/br/build-xea3/host/usr/libexec/gcc/xtensa-buildroot-linux-uclibc/4.8.3/lto-wrapper
Target: xtensa-buildroot-linux-uclibc
Configured with: ./configure --prefix=/home/jcmvbkbc/tmp/br/build-xea3/host/usr
--sysconfdir=/home/jcmvbkbc/tmp/br/build-xea3/host/etc --enable-static
--target=xtensa-buildroot-linux-uclibc
--with-sysroot=/home/jcmvbkbc/tmp/br/build-xea3/host/usr/xtensa-buildroot-linux-uclibc/sysroot
--disable-__cxa_atexit --with-gnu-ld --disable-libssp --disable-multilib
--with-gmp=/home/jcmvbkbc/tmp/br/build-xea3/host/usr
--with-mpfr=/home/jcmvbkbc/tmp/br/build-xea3/host/usr --enable-target-optspace
--disable-libsanitizer --disable-tls --disable-libmudflap --enable-threads
--with-mpc=/home/jcmvbkbc/tmp/br/build-xea3/host/usr --without-isl
--without-cloog --disable-decimal-float --with-pkgversion='Buildroot
2014.08-00004-ge3e7af8' --with-bugurl=http://bugs.buildroot.net/
--enable-languages=c,c++
--with-build-time-tools=/home/jcmvbkbc/tmp/br/build-xea3/host/usr/xtensa-buildroot-linux-uclibc/bin
--enable-shared --disable-libgomp
Thread model: posix
gcc version 4.8.3 (Buildroot 2014.08-00004-ge3e7af8) 

and

Using built-in specs.
COLLECT_GCC=/home/jcmvbkbc/ws/tensilica/projects/201409-call0/build-5.0.0-windowed-check/root/bin/xtensa-buildroot-linux-uclibc-gcc
COLLECT_LTO_WRAPPER=/home/jcmvbkbc/ws/tensilica/projects/201409-call0/build-5.0.0-windowed-check/root/libexec/gcc/xtensa-buildroot-linux-uclibc/5.0.0/lto-wrapper
Target: xtensa-buildroot-linux-uclibc
Configured with: ../gcc/configure
--prefix=/home/jcmvbkbc/ws/tensilica/projects/201409-call0/build-5.0.0-windowed-check/root
--target=xtensa-buildroot-linux-uclibc --disable-shared --disable-libssp
--disable-libisl --enable-languages=c,c++
--with-sysroot=/home/jcmvbkbc/tmp/br/build-dejagnu-windowed/host/usr/xtensa-buildroot-linux-uclibc/sysroot
--disable-threads --disable-tls
Thread model: single
gcc version 5.0.0 20150303 (experimental) (GCC)