https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89132
Bug ID: 89132
Summary: missing -Wcast-align casting the address of a function
to a more aligned pointer type
Product: gcc
Version: 9.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: msebor at gcc dot gnu.org
Target Milestone: ---
The -Wcast-align warning is documented to
Warn whenever a pointer is cast such that the required alignment of the
target is increased. For example, warn if a char * is cast to an int * on
machines where integers can only be accessed at two- or four-byte boundaries.
The strict form of the warning is documented to trigger "regardless of the
target machine."
The following test case shows that the warning fails to trigger when the
address of a function is cast to a pointer to a type with a stricter alignment.
The test case was compiled for the strictly aligned SPARC but the same problem
affects even x86.
As an aside, it would be helpful to include the alignment in the diagnostic so
that users can more easily tell what the expectations are and by how much
they're off.
$ cat u.c && /build/sparc-solaris2.11/gcc-svn/gcc/xgcc -B
/build/sparc-solaris2.11/gcc-svn/gcc -S -Wall -Wextra -Wcast-align=strict
-o/dev/stdout -xc u.c
int i = 1;
long long *p = (long long*)&i; // -Wcast-align (good)
void f (void) { }
long long *q = (long long*)f; // missing -Wcast-align
.file "u.c"
u.c:2:16: warning: cast increases required alignment of target type
[-Wcast-align]
2 | long long *p = (long long*)&i; // -Wcast-align (good)
| ^
.section ".text"
.global i
.section ".data"
.align 4
.type i, #object
.size i, 4
i:
.long 1
.global p
.align 4
.type p, #object
.size p, 4
p:
.long i
.section ".text"
.align 4
.global f
.type f, #function
.proc 020
f:
save %sp, -96, %sp
nop
return %i7+8
nop
.size f, .-f
.global q
.section ".data"
.align 4
.type q, #object
.size q, 4
q:
.long f
.ident "GCC: (GNU) 9.0.0 20190118 (experimental)"
