https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115541
Bug ID: 115541
Summary: gcc generates calls to memcpy that violate the memcpy
specification
Product: gcc
Version: 14.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: mikulas at artax dot karlin.mff.cuni.cz
Target Milestone: ---
struct s {
int a[10000];
};
void assign(struct s *s1, struct s *s2)
{
*s1 = *s2;
}
compiling it with -O2 results in this:
assign:
subq $8, %rsp
movl $40000, %edx
call memcpy@PLT
addq $8, %rsp
ret
The problem is that when we call the function "assign" with s1 equal to s2, gcc
generates a call to memcpy with overlapping arguments and that violates the C
standard.
Note that if the memcpy implementation uses an instruction such as "DC ZVA" to
zero cache line without reading it from memory, this becomes a practical
problem.
gcc should generate memmove instead of memcpy in this case.
