Version Information
[EMAIL PROTECTED] ~]$ arm-elf-gcc -v
Using built-in specs.
Target: arm-elf
Configured with: ../gcc-4.1.1/configure
--prefix=/usr/local/armdev-926ej-s-4.1.1 --target=arm-elf --enable-languages=c
--with-float=soft --enable-interwork --enable-multilib --with-cpu=arm926ej-s
--disable-threads --with-dwarf2 --without-headers
Thread model: single
gcc version 4.1.1
[EMAIL PROTECTED] ~]$
Reproduction Steps
[EMAIL PROTECTED] ~]$ arm-elf-gcc -Os -save-temps -c -S sample.c
[EMAIL PROTECTED] ~]$
[ sample.i attached to this bug report ]
Analysis of the bug
The bug appears in the generated assembly of the function gc_lock_held(int).
The function gc_memmove_down(void *, const void *, size_t) is inlined into this
function during compilation. That function includes the following inline
assembly statement:
asm("0:\t"
"ldmia %[src]!, { r4 - r11 }\n\t"
"stmia %[dest]!, { r4 - r11 }\n\t"
"sub %[count], %[count], #32\n\t"
"cmp %[count], #32\n\t"
"bhs 0b\n\t"
: [src] "+r" (src), [dest] "+r" (dest), [count] "+r" (count)
:
: "r4", "r5", "r6", "r7", "r8", "r9", "r10", "r11", "cc",
"memory");
The statement lists several clobbered hard registers, as described in this part
of the GCC manual:
http://gcc.gnu.org/onlinedocs/gcc-4.1.1/gcc/Extended-Asm.html#Extended-Asm. In
particular, "r11" is one of the clobbered hard registers. In the ARM
architecture, "r11" is a synonym for "fp". This inline assembly statement is
exported into the generated .s file on line 215.
The bug appears on line 241, where we see the following instruction:
str r3, [fp, #0]
A quick hand simulation of the generated assembly code shows that we can reach
this statement without reloading a valid value into fp. Thus, fp is
dereferenced despite having been clobbered by the inline assembly statement.
Because "r11" was listed as a clobbered hard register, gcc should have restored
the value of this register before using it.
Replacing "r11" with "fp" in the clobbered hard register list does not change
the generated code.
--
Summary: Clobbered hard register is not restored before
subsequent use
Product: gcc
Version: 4.1.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: inline-asm
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: dpm at danger dot com
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30579
