Hi Topi,
On 11/11/21 19:04, Topi Miettinen wrote:
A bit surprisingly, mmap(2) returns ENOMEM when the virtual address
space of the CPU is exceeded.
The expectation could be EINVAL instead ("We don't like _addr_,
length, or offset (e.g., they are _too large_, or not aligned on a
page boundary)").
This is demonstrated with the following program:
#include <stdio.h>
#include <sys/mman.h>
int main(void) {
for (int i = 12; i < 64; i++) {
void *addr = mmap((void *)(1UL << i), 4096, PROT_NONE,
MAP_ANON | MAP_FIXED_NOREPLACE | MAP_PRIVATE,
-1, 0);
if (addr == MAP_FAILED)
fprintf(stderr, "mmap %lx: %m\n", (1UL << i));
continue;
munmap(addr, 4096);
}
}
It gives the following output when running on CPU with 48 bit VA
space:
mmap 800000000000: Cannot allocate memory
mmap 1000000000000: Cannot allocate memory
mmap 2000000000000: Cannot allocate memory
mmap 4000000000000: Cannot allocate memory
mmap 8000000000000: Cannot allocate memory
mmap 10000000000000: Cannot allocate memory
mmap 20000000000000: Cannot allocate memory
mmap 40000000000000: Cannot allocate memory
mmap 80000000000000: Cannot allocate memory
mmap 100000000000000: Cannot allocate memory
mmap 200000000000000: Cannot allocate memory
mmap 400000000000000: Cannot allocate memory
mmap 800000000000000: Cannot allocate memory
mmap 1000000000000000: Cannot allocate memory
mmap 2000000000000000: Cannot allocate memory
mmap 4000000000000000: Cannot allocate memory
mmap 8000000000000000: Cannot allocate memory
Signed-off-by: Topi Miettinen <toiwoton@xxxxxxxxx>
Patch applied!
Thanks,
Alex
---
man2/mmap.2 | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/man2/mmap.2 b/man2/mmap.2
index 96b7444b0..59fd5c904 100644
--- a/man2/mmap.2
+++ b/man2/mmap.2
@@ -603,6 +603,11 @@ limit, described in
.BR getrlimit (2),
would have been exceeded.
.TP
+.B ENOMEM
+We don't like
+.IR addr ,
+because it exceeds the virtual address space of the CPU.
+.TP
.B EOVERFLOW
On 32-bit architecture together with the large file extension
(i.e., using 64-bit
--
Alejandro Colomar
Linux man-pages comaintainer; http://www.kernel.org/doc/man-pages/
http://www.alejandro-colomar.es/
