From: Ammar Faizi <ammarfaizi2@xxxxxxxxxxx>
Use a struct initializer instead of memset(). It simplifies the C code
plus effectively reduces the code size.
Extra bonus on x86-64. It reduces the stack allocation because it
doesn't need to allocate stack for the local variable @range. It can
just use 128 bytes of redzone below the `%rsp` (redzone is only
available in a leaf function).
Before this patch:
```
0000000000003910 <io_uring_register_file_alloc_range>:
3910: push %rbp
3911: push %r15
3913: push %r14
3915: push %rbx
3916: sub $0x18,%rsp
391a: mov %edx,%r14d
391d: mov %esi,%ebp
391f: mov %rdi,%rbx
3922: lea 0x8(%rsp),%r15
3927: mov $0x10,%edx
392c: mov %r15,%rdi
392f: xor %esi,%esi
3931: call 3a00 <__uring_memset>
3936: mov %ebp,0x8(%rsp)
393a: mov %r14d,0xc(%rsp)
393f: mov 0xc4(%rbx),%edi
3945: mov $0x1ab,%eax
394a: mov $0x19,%esi
394f: mov %r15,%rdx
3952: xor %r10d,%r10d
3955: syscall
3957: add $0x18,%rsp
395b: pop %rbx
395c: pop %r14
395e: pop %r15
3960: pop %rbp
3961: ret
3962: cs nopw 0x0(%rax,%rax,1)
396c: nopl 0x0(%rax)
```
After this patch:
```
0000000000003910 <io_uring_register_file_alloc_range>:
3910: mov %esi,-0x10(%rsp) # set range.off
3914: mov %edx,-0xc(%rsp) # set range.len
3918: movq $0x0,-0x8(%rsp) # zero the resv
3921: mov 0xc4(%rdi),%edi
3927: lea -0x10(%rsp),%rdx
392c: mov $0x1ab,%eax
3931: mov $0x19,%esi
3936: xor %r10d,%r10d
3939: syscall
393b: ret
```
Signed-off-by: Ammar Faizi <ammarfaizi2@xxxxxxxxxxx>
---
src/register.c | 9 ++++-----
1 file changed, 4 insertions(+), 5 deletions(-)
diff --git a/src/register.c b/src/register.c
index 5fdc6e5..ac4c9e3 100644
--- a/src/register.c
+++ b/src/register.c
@@ -333,11 +333,10 @@ int io_uring_register_sync_cancel(struct io_uring *ring,
int io_uring_register_file_alloc_range(struct io_uring *ring,
unsigned off, unsigned len)
{
- struct io_uring_file_index_range range;
-
- memset(&range, 0, sizeof(range));
- range.off = off;
- range.len = len;
+ struct io_uring_file_index_range range = {
+ .off = off,
+ .len = len
+ };
return __sys_io_uring_register(ring->ring_fd,
IORING_REGISTER_FILE_ALLOC_RANGE, &range,
--
Ammar Faizi
