Sign-extension error in RV64 when build optimization is enabled

[zhengaooo]

my toolchain was built by command ./configure && make linux on unbuntu.
And when compile bellow code, the result is quite different with/without build optimization (-O1 or higher level)

#include <stdio.h>
#define TEE_ERROR_ITEM_NOT_FOUND          (0xFFFF0008U)

unsigned int do_something(unsigned long tmp);

asm(
    ".globl do_something              \n\t"
    "do_something:                    \n\t"
    "ret                     \n\t"
);

int main() {

        unsigned int res = TEE_ERROR_ITEM_NOT_FOUND;
        unsigned long test = res;
       if(test == res)
                printf("a. %s %llx %llx\n",__TIMESTAMP__, res, test);

        if (test == TEE_ERROR_ITEM_NOT_FOUND)
                printf("b. %s %llx %llx\n",__TIMESTAMP__, res, test);

        res = do_something(test);

        if (res != TEE_ERROR_ITEM_NOT_FOUND)
                printf("c. %s %llx %llx\n",__TIMESTAMP__, res, test);
        return res;
}

it shouldn't print "c. %s %llx...", but when use -O1, it will print this sentence, seems it will ignore sign-extension when enable optimization.
it easy to verify.
look forward for your opinion

[cmuellner]

Your code has a few issues:

• You use "%llx" for res, instead of "%x"
• You use "%llx" for test, instead of "%llx"
• You are assigning a value to res with res = do_something(test);, but do_something does not set a return value in a0

The last point is probably the source of your issue.
If you assure the compiler that you will set a0 in do_something, but you don't do that, then a0 will be undefined.

I have fixed the code as follows:

#include <stdio.h>
#define TEE_ERROR_ITEM_NOT_FOUND          (0xFFFF0008U)

unsigned int do_something(unsigned long tmp);

asm(
        ".globl do_something    \n\t"
        "do_something:          \n\t"
        "li      a0,-65536      \n\t"
        "addi    a0,a0,8        \n\t"
        "ret                    \n\t"
);

int main()
{
        unsigned int res = TEE_ERROR_ITEM_NOT_FOUND;
        unsigned long test = res;

        if(test == res)
                printf("a. %s %x %lx\n",__TIMESTAMP__, res, test);

        if (test == TEE_ERROR_ITEM_NOT_FOUND)
                printf("b. %s %x %lx\n",__TIMESTAMP__, res, test);

        res = do_something(test);

        if (res != TEE_ERROR_ITEM_NOT_FOUND)
                printf("c. %s %x %lx\n",__TIMESTAMP__, res, test);

        return res;
}

With this changes applied, I can't reproduce your issue.

[TommyMurphyTM1234]

In a case such as this it would also make sense to look at the generated code (e.g. disassembly listing) for the two cases (with and without optimisation) to compare and contrast the two.

[zhengaooo]

Your code has a few issues:

• You use "%llx" for res, instead of "%x"
• You use "%llx" for test, instead of "%llx"
• You are assigning a value to res with res = do_something(test);, but do_something does not set a return value in a0

The last point is probably the source of your issue. If you assure the compiler that you will set a0 in do_something, but you don't do that, then a0 will be undefined.

I have fixed the code as follows:

#include <stdio.h>
#define TEE_ERROR_ITEM_NOT_FOUND (0xFFFF0008U)

unsigned int do_something(unsigned long tmp);

asm(
".globl do_something \n\t"
"do_something: \n\t"
"li a0,-65536 \n\t"
"addi a0,a0,8 \n\t"
"ret \n\t"
);

int main()
{
unsigned int res = TEE_ERROR_ITEM_NOT_FOUND;
unsigned long test = res;

    if(test == res)
            printf("a. %s %x %lx\n",__TIMESTAMP__, res, test);

    if (test == TEE_ERROR_ITEM_NOT_FOUND)
            printf("b. %s %x %lx\n",__TIMESTAMP__, res, test);

    res = do_something(test);

    if (res != TEE_ERROR_ITEM_NOT_FOUND)
            printf("c. %s %x %lx\n",__TIMESTAMP__, res, test);

    return res;

}
With this changes applied, I can't reproduce your issue.

About the third point, "unsigned long tmp" is formal parameter, and test is actual parameter, when "res = do_something(test);" this setence executed, the value of $a0 in do_something will be set as test, and then assign to res, is it?

In some scenarios—particularly during system calls—certain assembly function do not process input parameters and simply return. in this case will cause this error. I'm not sure it OS error or Toolchain error.
But the behavior is different in this scenario with/without optimization. In my view, this is unreasonable.

[zhengaooo]

In a case such as this it would also make sense to look at the generated code (e.g. disassembly listing) for the two cases (with and without optimisation) to compare and contrast the two.

Yes, optimization will remove some sign-extension instruction like sext.w