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MESC TOOL NEWS:
MESCT-NC308WA_2-001216D
Please take note of the following problems in using C compiler NC308WA (with an assembler and integrated development environment) for the M16C/80 series MCUs:
- On pointers pointing to functions
- On using a structure as an actual argument to a function with varying numbers of arguments
- Problem on Pointers Pointing to Functions
- 1.1 Versions Concerned
- NC308WA V.1.00 Release 1 -- V.3.10 Release 1
- 1.2 Description
- When a pointer to a function is assigned to a register variable and the address of the function is assigned to a variable of the pointer, only the lower 16 bits of the address are set to the variable.
- 1.3 Conditions
- This problem occurs if the following three conditions are satisfied:
- (1) A pointer to a function is declared to be a register variable.
- (2) The address of the function is assigned to the pointer in (1) or used for initializing it.
- (3) Option "-fenable_register(-fER)" is used at compilation.
- In NC308WA V.3.10 Release 1, furthermore, this problem also arises if the following three conditions are satisfied:
- (1) A pointer to a function is declared to be an auto variable or register variable.
- (2) The address of the function is assigned to the pointer in (1) or used for initializing it.
- (3) Any one or more of the options -O, -O[1-5], -OR, and -OS are used at compilation.
[Example]
------------------------------------------------------------------
int func(void);
int main(void)
{
register int (*p)(void) = func; /* The address of the function
becomes incorrect */
int i;
i = p(); /* Not the function "func" but an incorrect address
is called indirectly */
return i;
}
------------------------------------------------------------------
- 1.4 Workaround
- When the address of a function is assigned to a pointer, make sure to declare or define the function using type modifier "far".
-----------------------------------------------------------------
far int func(void);
-----------------------------------------------------------------
- 1.5 Schedule of Fixing Problem
- We plan to fix this problem in our next release.
NC308WA Precaution
MESCT-NC308WA_2-001216D
- Problem on Using a Structure as an Actual Argument of a Function with Varying Numbers of Arguments
- 2.1 Versions Concerned
- NC308WA V.1.00 Release 1 ~ V.3.10 Release 1
- 2.2 Description
- If a structure whose size is an odd number of bytes is used as an actual argument to a function with varying numbers of arguments, no actual arguments described after the structure are accessible.
- 2.3 Conditions
- This problem occurs if the following four conditions are satisfied:
- (1) The va_arg macro that is defined in the "stdarg.h" file is used.
- (2) The second argument to the va_arg macro is a structure the size of which is an odd number of bytes.
- (3) The last of the declared formal arguments to a function that takes varying numbers of arguments or the actual argument corresponding to an omitted formal argument is a structure the size of which is an odd number of bytes.
- (4) Another actual argument is described after the structure in (3) above.
[Example]
--------------------------------------------------------------
#include <stdarg.h>
struct s { /* A structure with an odd number of bytes */
long l;
char c;
};
int func(int a,...);
int main(void)
{
struct s s1;
i = func(1, s1, 0x1234); /* Conditions (3) and (4) */
}
int func(int a,...)
{
int ii;
struct s s2;
va_list ap;
va_start(ap, a);
s2 = va_arg(ap, struct s); /* Conditions (1) and (2) */
ii = va_arg(ap, int); /* Conditions (1) and (4) */
va_end(ap);
return ii;
}
--------------------------------------------------------------
- * In the above example, argument 0x1234 in "i = func(1, s1, 0x1234);" cannot be accessed correctly.
- 2.4 Workaround
- Every structure used as an actual argument to a function with varying numbers of arguments must be defined as an even number of bytes in size by declaring a dummy data.
-----------------------------------------------------------------
struct s {
long l;
char c;
char dummy; /* padding */
};
-----------------------------------------------------------------
- 2.5 Schedule of Fixing Problem
- We plan to fix this problem in our next release.
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