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[PATCH] linux-user: Fix brk() to release pages
From: |
Helge Deller |
Subject: |
[PATCH] linux-user: Fix brk() to release pages |
Date: |
Fri, 23 Dec 2022 11:16:28 +0100 |
The current brk() implementation does not de-allocate pages if a lower
address is given compared to earlier brk() calls.
But according to the manpage, brk() shall deallocate memory in this case
and currently it breaks a real-world application, specifically building
the debian gcl package in qemu-user.
Fix this issue by reworking the qemu brk() implementation.
Tested with the C-code testcase included in qemu commit 4d1de87c750, and
by building debian package of gcl in a hppa-linux guest on a x86-64
host.
Signed-off-by: Helge Deller <deller@gmx.de>
---
linux-user/syscall.c | 43 +++++++++++++++++++++++--------------------
1 file changed, 23 insertions(+), 20 deletions(-)
diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index 4fee882cd7..d306b02e21 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -838,13 +838,12 @@ static inline int host_to_target_sock_type(int host_type)
}
static abi_ulong target_brk;
-static abi_ulong target_original_brk;
static abi_ulong brk_page;
void target_set_brk(abi_ulong new_brk)
{
- target_original_brk = target_brk = HOST_PAGE_ALIGN(new_brk);
- brk_page = HOST_PAGE_ALIGN(target_brk);
+ target_brk = TARGET_PAGE_ALIGN(new_brk);
+ brk_page = HOST_PAGE_ALIGN(new_brk);
}
//#define DEBUGF_BRK(message, args...) do { fprintf(stderr, (message), ##
args); } while (0)
@@ -855,29 +854,29 @@ abi_long do_brk(abi_ulong new_brk)
{
abi_long mapped_addr;
abi_ulong new_alloc_size;
+ abi_ulong new_host_brk_page;
/* brk pointers are always untagged */
+ new_brk = TARGET_PAGE_ALIGN(new_brk);
+ new_host_brk_page = HOST_PAGE_ALIGN(new_brk);
+
DEBUGF_BRK("do_brk(" TARGET_ABI_FMT_lx ") -> ", new_brk);
- if (!new_brk) {
+ if (!new_brk || new_brk == target_brk) {
DEBUGF_BRK(TARGET_ABI_FMT_lx " (!new_brk)\n", target_brk);
return target_brk;
}
- if (new_brk < target_original_brk) {
- DEBUGF_BRK(TARGET_ABI_FMT_lx " (new_brk < target_original_brk)\n",
- target_brk);
- return target_brk;
- }
- /* If the new brk is less than the highest page reserved to the
- * target heap allocation, set it and we're almost done... */
- if (new_brk <= brk_page) {
- /* Heap contents are initialized to zero, as for anonymous
- * mapped pages. */
- if (new_brk > target_brk) {
- memset(g2h_untagged(target_brk), 0, new_brk - target_brk);
- }
+ /* Release heap if necesary */
+ if (new_brk < target_brk) {
+ /* empty remaining bytes in (possibly larger) host page */
+ memset(g2h_untagged(new_brk), 0, new_host_brk_page - new_brk);
+
+ /* free unused host pages and set new brk_page */
+ target_munmap(new_host_brk_page, brk_page - new_host_brk_page);
+ brk_page = new_host_brk_page;
+
target_brk = new_brk;
DEBUGF_BRK(TARGET_ABI_FMT_lx " (new_brk <= brk_page)\n", target_brk);
return target_brk;
@@ -889,10 +888,14 @@ abi_long do_brk(abi_ulong new_brk)
* itself); instead we treat "mapped but at wrong address" as
* a failure and unmap again.
*/
- new_alloc_size = HOST_PAGE_ALIGN(new_brk - brk_page);
- mapped_addr = get_errno(target_mmap(brk_page, new_alloc_size,
+ new_alloc_size = new_host_brk_page - brk_page;
+ if (new_alloc_size) {
+ mapped_addr = get_errno(target_mmap(brk_page, new_alloc_size,
PROT_READ|PROT_WRITE,
MAP_ANON|MAP_PRIVATE, 0, 0));
+ } else {
+ mapped_addr = brk_page;
+ }
if (mapped_addr == brk_page) {
/* Heap contents are initialized to zero, as for anonymous
@@ -905,7 +908,7 @@ abi_long do_brk(abi_ulong new_brk)
memset(g2h_untagged(target_brk), 0, brk_page - target_brk);
target_brk = new_brk;
- brk_page = HOST_PAGE_ALIGN(target_brk);
+ brk_page = new_host_brk_page;
DEBUGF_BRK(TARGET_ABI_FMT_lx " (mapped_addr == brk_page)\n",
target_brk);
return target_brk;
--
2.38.1
- [PATCH] linux-user: Fix brk() to release pages,
Helge Deller <=