All Questions
Tagged with gcc inline-assembly
828
questions
1
vote
1
answer
58
views
gnu inline assembly constraint `i` for memory address
Recetly, this function rip_rel_ptr has been added to Linux kernel.
https://elixir.bootlin.com/linux/latest/source/arch/x86/include/asm/asm.h#L118.
I can compile the kernel, but when I copy this ...
- 367
8
votes
1
answer
230
views
Purpose of '*&x' in inline assembly?
Looking at some x86_64 GCC inline assembly, I have come across the following construct:
int x;
__asm__( "<opcode> %0" : "=m" (*&x) );
^^^
...
- 69.5k
2
votes
1
answer
107
views
What does `+&` mean in gcc inline assembly?
I'm aware that when using gcc inline assembly, if you don't specify otherwise, it assumes that you consume all your inputs before you write any ouput operand. If you actually want to write to an ...
1
vote
1
answer
116
views
Using FSIN through inline-assembly
I want to use x87's FSIN through gcc's / clang's inline assembly. How would a sin()-function using an __asm__-block internally for that look like with a 64 bit double parameter ? Using __builtin_sin() ...
0
votes
0
answers
43
views
the difference between two style of inline ASM
My code print FAIL as follow:
Need someone to explain the difference.
I want to know the difference between
__asm__ __volatile__(
"addl %1,%0;"
:"=r"(sum)
:"r"...
0
votes
1
answer
53
views
How can I create an Inline assembly command with a multi-variable register offset?
The following code, using gcc for ARMv4, is perfectly fine:
asm("strb.w r2, [r0, #24 + 8 * 1]");
Now, if I try the following:
asm("strb.w r2, [r0, %[offset] + %[delta] * %[scale]]"...
- 257
0
votes
0
answers
48
views
gcc inline assembly fails for compiler option -O2 [duplicate]
When the compiler optimize option -O2 is set, the output is empty
dst:
However, if -O2 is removed, the output appears
dst: 123456789
Why does adding -O2 cause nothing to display (-O1 works fine)?
...
- 2,125
0
votes
1
answer
162
views
Why is this inline ASM function adding the first input operand twice? [duplicate]
I'm a beginner to assembly and a novice programmer in general. I'm trying to wrap my head around the basics of assembly by writing some basic inline asm functions in C++. I'm compiling with GNU g++, ...
- 3
2
votes
0
answers
253
views
How to write _start function to call the main function in C
By using inline assembly asm volatile, how can I implement _start function in C which can call the main function
int main(int argc, char *argv[], char *envp[])
I tried alot, but it didn't work at all,...
- 43
1
vote
1
answer
88
views
Cannot specify the operands when using inline asm outside a function
My code is
unsigned long user_stack_pointer;
__asm__(
".global exception_handling_entry\n"
"exception_handling_entry:\n"
"add %0, sp, x0\n"
: "=r&...
- 123
0
votes
0
answers
52
views
What do the numbers in "%0" or "%1" mean in C/C++ GCC Inline Assembly [duplicate]
I'm Reading the gcc documentation about the inline assembly,there was an operand syntax like %0,%1,%2 what this number mean ?, in their documentation this is not explained.
0
votes
0
answers
48
views
Why is RISC-V GCC breaking my code when optimizations are enabled? [duplicate]
I have the following C code for 32-bit RISC-V:
static void test(uint32_t key, uint32_t chr, uint32_t state)
{
char s[2];
if(state != KEYSTATE_PRESSED) { return; }
if(!isprint(chr)) { ...
- 1,068
0
votes
1
answer
59
views
gcc inline asm / constraints / "r" relates to "l" like "g" to ...?
I'm trying to compile this for an ARM Cortex-M0+ (STM32G030) with arm-none-eabi-gcc:
asm("ldrb %0, [%1, %2]\n" : "=l" (v) : "l" (R.a+(o&~31)) , "g" (o&...
- 119
3
votes
1
answer
337
views
RISC-V GCC Compiler compiles ASM code incorrectly
I am writing an embedded C program to test a hardware IP that I have developed on an FPGA board. I was playing with the RISC-V GCC ASM syntax and found this weird issue.
This is the code that I ...
- 155
0
votes
0
answers
171
views
RISCV64 `li` pseudo instruction and inline asm operand constraints
I work on bare-metal with C99.
Please consider...
#define FOO 0x234567894567ULL
extern void someFunction(void);
void example(void) __attribute__((naked));
void
example(void)
{
__asm__ volatile(
...
- 1,054