Hello Razvan,
On 3/3/26 20:01, razvan ghiorghe wrote:
Hi,
I'd like to kindly ping this patch. It has been a few weeks since submission
and I haven't received any feedback yet.
I'm working on getting familiar with the contribution flux. Any review, even
brief comments on the approach would be very helpful!
First of all, I could not find the "v2" version of your patch.
It's not in the qemu mail archives, only in your mail below.
Did you sent a v2 version at all?
More importantly, I can confirm with the testcase from
https://gitlab.com/qemu-project/qemu/-/issues/3105,
that the problem exists.
Testcase works on a physical hppa box, but fails in qemu-linux-user.
The patch seems ok, but it did not work for me.
Without your patch:
(hppa-chroot)root@p100:/# ./a.out
mremap with old_size=0 failed: Bad address
-> problem exists as you described.
With your patch:
(hppa-chroot)root@p100:/# ./a.out
qemu-hppa-static: ../../qemu/linux-user/mmap.c:1142: target_mremap: Assertion
`h2g_valid(host_addr)' failed.
Aborted (core dumped) ./a.out
More info:
(hppa-chroot)root@p100:/# QEMU_LOG=strace ./a.out
...
7087 mmap2(NULL,4096,PROT_READ|PROT_WRITE,MAP_SHARED|MAP_ANONYMOUS,-1,0) =
0x45214000
7087 mremap(1159806976,0,8192,1,0,1159087572)
qemu-hppa-static: ../../qemu/linux-user/mmap.c:1142: target_mremap: Assertion
`h2g_valid(host_addr)' failed.
Aborted (core dumped) QEMU_LOG=strace ./a.out
Helge
Thanks in advance,
Razvan
În dum., 1 feb. 2026 la 03:08, Razvan Ghiorghe <[email protected]
<mailto:[email protected]>> a scris:
When old_size is zero and old_address refers to a shareable mapping,
mremap() should create a new mapping of the same pages according to the
mremap(2) man page. The MREMAP_MAYMOVE flag must be specified in this case.
Previously, QEMU's target_mremap() rejected this valid case with EFAULT
during
the initial validation, before checking for the special old_size == 0
behaviour.
This patch adds proper handling for old_size == 0:
- Validates that MREMAP_MAYMOVE flag is set (required by man spec)
- Passes the call through to the host mremap()
- Creates a new mapping without invalidating the original, with both
beeing valid and sharing the same physical memory frames.
Tested with the reproducer from the issue on qemu-riscv64.
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/3105
<https://gitlab.com/qemu-project/qemu/-/issues/3105>
Signed-off-by: Razvan Ghiorghe <[email protected]
<mailto:[email protected]>>
---
linux-user/mmap.c | 32 ++++++++++++++++++++++++++++++++
1 file changed, 32 insertions(+)
diff --git a/linux-user/mmap.c b/linux-user/mmap.c
index 4bcfaf7894..b1a84eb60a 100644
--- a/linux-user/mmap.c
+++ b/linux-user/mmap.c
@@ -1117,6 +1117,38 @@ abi_long target_mremap(abi_ulong old_addr, abi_ulong
old_size,
errno = EINVAL;
return -1;
}
+
+ if (!old_size) {
+ if (!(flags & MREMAP_MAYMOVE)) {
+ errno = EINVAL;
+ return -1;
+ }
+ mmap_lock();
+ if (flags & MREMAP_FIXED) {
+ host_addr = mremap(g2h_untagged(old_addr), old_size, new_size,
+ flags, g2h_untagged(new_addr));
+ } else {
+ host_addr = mremap(g2h_untagged(old_addr), old_size, new_size,
+ flags);
+ }
+
+ if (host_addr == MAP_FAILED) {
+ mmap_unlock();
+ return -1;
+ }
+ new_addr = h2g(host_addr);
+ prot = page_get_flags(old_addr);
+ /*
+ * For old_size zero, there is nothing to clear at old_addr.
+ * Only set the flags for the new mapping. They both are valid.
+ */
+ page_set_flags(new_addr, new_addr + new_size - 1,
+ prot | PAGE_VALID, PAGE_VALID);
+ shm_region_rm_complete(new_addr, new_addr + new_size - 1);
+ mmap_unlock();
+ return new_addr;
+ }
+
if (!guest_range_valid_untagged(old_addr, old_size)) {
errno = EFAULT;
return -1;
--
2.43.0
