Hello everyone,
I have a question about the build of ASan's runtime for arm with -mthumb
and fno-omit-frame-pointer.
So, by default libasan has "-fomit-frame-pointer" option.
The problem occurs when "-fno-omit-frame-pointer" option is adding
alongside with "-mthumb", the build is failing with error:
../../../../libsanitizer/sanitizer_common/sanitizer_linux.cc: In
function '__sanitizer::uptr __sanitizer::internal_clone(int (*)(void*),
void*, int, void*, int*, void*, int*)':
../../../../libsanitizer/sanitizer_common/sanitizer_linux.cc:1134:1:
error: r7 cannot be used in asm here
}
And the problem is inside internal_clone function,
I've added reduced test case:
$cat clone.cc
#define __NR_clone 120
#define __NR_exit 1
using uptr = unsigned int;
unsigned int EINVAL = 1;
uptr internal_clone(int (*fn)(void *), void *child_stack, int flags,
void *arg,
int *parent_tidptr, void *newtls, int *child_tidptr) {
unsigned int res;
if (!fn || !child_stack)
return -EINVAL;
child_stack = (char *)child_stack - 2 * sizeof(unsigned int);
((unsigned int *)child_stack)[0] = (uptr)fn;
((unsigned int *)child_stack)[1] = (uptr)arg;
register int r0 __asm__("r0") = flags;
register void *r1 __asm__("r1") = child_stack;
register int *r2 __asm__("r2") = parent_tidptr;
register void *r3 __asm__("r3") = newtls;
register int *r4 __asm__("r4") = child_tidptr;
register int r7 __asm__("r7") = __NR_clone;
#if __ARM_ARCH > 4 || defined (__ARM_ARCH_4T__)
# define ARCH_HAS_BX
#endif
#if __ARM_ARCH > 4
# define ARCH_HAS_BLX
#endif
#ifdef ARCH_HAS_BX
# ifdef ARCH_HAS_BLX
# define BLX(R) "blx " #R "\n"
# else
# define BLX(R) "mov lr, pc; bx " #R "\n"
# endif
#else
# define BLX(R) "mov lr, pc; mov pc," #R "\n"
#endif
__asm__ __volatile__(
/* %r0 = syscall(%r7 = SYSCALL(clone),
* %r0 = flags,
* %r1 = child_stack,
* %r2 = parent_tidptr,
* %r3 = new_tls,
* %r4 = child_tidptr)
*/
/* Do the system call */
"swi 0x0\n"
/* if (%r0 != 0)
* return %r0;
*/
"cmp r0, #0\n"
"bne 1f\n"
/* In the child, now. Call "fn(arg)". */
"ldr r0, [sp, #4]\n"
"ldr ip, [sp], #8\n"
BLX(ip)
/* Call _exit(%r0). */
"mov r7, %7\n"
"swi 0x0\n"
"1:\n"
"mov %0, r0\n"
: "=r"(res)
: "r"(r0), "r"(r1), "r"(r2), "r"(r3), "r"(r4),
"r"(r7),
"i"(__NR_exit)
: "memory");
return res;
}
$armv7l-linux-gnueabi-g++ -o clone.s clone.cc -fno-omit-frame-pointer
-mthumb -S
clone.cc: In function ‘uptr internal_clone(int (*)(void*), void*, int,
void*, int*, void*, int*)’:
clone.cc:70:1: error: r7 cannot be used in asm here
As far as I understood, r7 register is using for syscall number, r0 for
return value, and r1 - r6 for syscall arguments, by the way r7 for arm
with THUMB2 mode is using as frame pointer and it looks like we have a
conflict in this case.
So, the question is should it be considered as a bug or not, because,
probably, no one needs libasan with "-mthumb" and
"-fno-omit-frame-pointer", and by default it works well with
"-fomit-frame-pointer" ?
