diff options
Diffstat (limited to 'src')
| -rw-r--r-- | src/tests/math_test.c | 78 |
1 files changed, 74 insertions, 4 deletions
diff --git a/src/tests/math_test.c b/src/tests/math_test.c index fe61e29c1..14c9ee3ee 100644 --- a/src/tests/math_test.c +++ b/src/tests/math_test.c @@ -44,6 +44,72 @@ __attribute__ (( noinline )) int flsl_var ( long value ) { } /** + * Check current stack pointer + * + * @ret stack A value at a fixed offset from the current stack pointer + * + * Used by check_divmod() + */ +static __attribute__ (( noinline )) void * stack_check ( void ) { + int a; + void *ret; + + /* Hide the fact that we are returning the address of a local + * variable, to prevent a compiler warning. + */ + __asm__ ( "\n" : "=g" ( ret ) : "0" ( &a ) ); + + return ret; +} + +/** + * Check division/modulus operation + * + * One aspect of the calling convention for the implicit arithmetic + * functions (__udivmoddi4() etc) is whether the caller or the callee + * is expected to pop any stack-based arguments. This distinction can + * be masked if the compiler chooses to uses a frame pointer in the + * caller, since the caller will then reload the stack pointer from + * the frame pointer and so can mask an error in the value of the + * stack pointer. + * + * We run the division operation in a loop, and check that the stack + * pointer does not change value on the second iteration. To prevent + * the compiler from performing various optimisations which might + * invalidate our intended test (such as unrolling the loop, or moving + * the division operation outside the loop), we include some dummy + * inline assembly code. + */ +#define check_divmod( dividend, divisor, OP ) ( { \ + uint64_t result; \ + int count = 2; \ + void *check = NULL; \ + \ + /* Prevent compiler from unrolling the loop */ \ + __asm__ ( "\n" : "=g" ( count ) : "0" ( count ) ); \ + \ + do { \ + /* Check that stack pointer does not change between \ + * loop iterations. \ + */ \ + if ( check ) { \ + assert ( check == stack_check() ); \ + } else { \ + check = stack_check(); \ + } \ + \ + /* Perform division, preventing the compiler from \ + * moving the division out of the loop. \ + */ \ + __asm__ ( "\n" : "=g" ( dividend ), "=g" ( divisor ) \ + : "0" ( dividend ), "1" ( divisor ) ); \ + result = ( dividend OP divisor ); \ + __asm__ ( "\n" : "=g" ( result ) : "0" ( result ) ); \ + \ + } while ( --count ); \ + result; } ) + +/** * Force a use of runtime 64-bit unsigned integer division * * @v dividend Dividend @@ -52,7 +118,8 @@ __attribute__ (( noinline )) int flsl_var ( long value ) { */ __attribute__ (( noinline )) uint64_t u64div_var ( uint64_t dividend, uint64_t divisor ) { - return ( dividend / divisor ); + + return check_divmod ( dividend, divisor, / ); } /** @@ -64,7 +131,8 @@ __attribute__ (( noinline )) uint64_t u64div_var ( uint64_t dividend, */ __attribute__ (( noinline )) uint64_t u64mod_var ( uint64_t dividend, uint64_t divisor ) { - return ( dividend % divisor ); + + return check_divmod ( dividend, divisor, % ); } /** @@ -76,7 +144,8 @@ __attribute__ (( noinline )) uint64_t u64mod_var ( uint64_t dividend, */ __attribute__ (( noinline )) int64_t s64div_var ( int64_t dividend, int64_t divisor ) { - return ( dividend / divisor ); + + return check_divmod ( dividend, divisor, / ); } /** @@ -88,7 +157,8 @@ __attribute__ (( noinline )) int64_t s64div_var ( int64_t dividend, */ __attribute__ (( noinline )) int64_t s64mod_var ( int64_t dividend, int64_t divisor ) { - return ( dividend % divisor ); + + return check_divmod ( dividend, divisor, % ); } /** |